This document discusses a method for predicting stereochemical reaction paths using orbital interactions between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of reacting species. The method involves identifying the HOMO and LUMO regions of the reacting molecules and determining which orientation leads to maximum overlap between the HOMO of one species and LUMO of the other. Several examples of intramolecular reactions are analyzed using this approach. The method is presented as a simple and practical way to interpret and predict favorable reaction stereochemistry.
This document outlines the contents of a book on functional group interconversions. It covers topics like alcohols, carboxylic acids and their derivatives, oxidation and reduction reactions, and C-C bond formation. Each chapter explains different reaction types and transformation pathways. The introduction discusses using natural products for medical treatments historically and the importance of functional group interconversions in organic synthesis.
The document provides an overview of chemical reactions, including:
1) It describes three main types of chemical reactions: substitution reactions, addition reactions, and elimination reactions.
2) It explains that nucleophiles are electron-rich reagents that donate electrons, while electrophiles are electron-poor reagents that accept electrons. Common nucleophiles include anions and molecules with lone pairs, while common electrophiles include protons and elements in Group 13.
3) Using examples, it illustrates how nucleophiles can donate electrons in substitution and addition reactions, and how electrophiles can accept electrons in these reactions.
This document summarizes a study that used X-ray crystallography and resonance Raman spectroscopy to characterize the oxo-molybdenum dithiolene complex (Tp*)MoO(qdt), which is a model system relevant to pyranopterin molybdenum enzyme active sites like sulfite oxidase. The compound was found to crystallize in the triclinic space group P1. Structural parameters of the first coordination sphere were similar to the related complex (Tp*)MoO(bdt), suggesting geometric effects are not major contributors to electronic structural differences between the two complexes. Raman spectroscopy provided evidence the dithiolene ligand interacts with the molybdenum center through
Polymorphism of Acylglycerols: A Stereochemical Perspectiverjcraven
The underlying cause for polymorphism in acyglycerols has puzzled researchers for more than 150 years. For the last 50 years or so, the subcell concept has been used to describe and understand this phenomenon. In general, there is a correlation between the crystal structure of the various polymorphs and the packing of the polymethylene chains (reflected in the subcell). This occurs because, for acylglcyerols, higher-melting polymorphs form due to an increase in packing efficiency for the polymethylene chains (i.e. packing efficiency increases α < β′ < β) . These same concepts are used to understand polymorphism in waxes and alkanes, and when applied to acylglycerols, they work reasonably well (i.e. as a rule of thumb). They are, however, of limited use in understanding more complex or exceptional polymorphic behaviors. In fact, progress in answering more difficult research problems is hindered, rather than helped, by the current reliance on the subcell concept.
In this work we provide a more fundamental understanding for polymorphism in acylglycerols. Using a stereochemical approach, we are able to provide solutions and mechanisms for research questions that have challenged (and remained unanswered) by many previous workers.
1) Chiral phosphoric acid catalyst PA-1 promotes the highly enantioselective ring-opening of meso-aziridines with a variety of functionalized aromatic thiols. The reaction proceeds in good yields and with up to 97% enantiomeric excess.
2) The reaction tolerates a wide range of substituted thiols, including those with electron-donating and -withdrawing groups, as well as heteroaromatic thiols. Alkyl thiols perform less well.
3) Different meso-aziridine substrates are also suitable, including those with fused ring systems or acyclic substituents. The reaction provides a simple method for the
More problems covering asymmetric synthesis. This time with examples of substrate control, chiral reagents, and chiral catalysis. Also another example of a synthesis.
This document summarizes a study on new electrically-driven chiral molecular switches based on axially dissymmetric 1,1'-binaphthyl and electrochromic viologens. The switches (R)-1 and (R)-2 were synthesized and characterized. Their optical properties, including absorption and circular dichroism spectra, changed drastically upon electrochemical redox reaction, demonstrating efficient chiroptical switching. The switches take advantage of the strong chirality of 1,1'-binaphthyl and the electrochromic behavior of viologens to achieve modulation of their chiroptical properties with an electric field.
1992 schottky barrier formation in conducting polymerspmloscholte
1. The authors studied thin films of poly(3-hexylthiophene) (PHT) and polypyrrole (PPY) on highly oriented pyrolytic graphite using scanning tunneling microscopy.
2. They observed semicrystalline order in the form of micro-islands connected by parallel polymer strands. The orientation of the strands is determined by the substrate.
3. For PPY films, they observed superhelical structures not previously reported. The apparent height of polymer strands was found to differ for positive and negative bias voltages, which the authors attribute to the formation of a Schottky barrier between the metallic tip and semiconducting polymer.
This document outlines the contents of a book on functional group interconversions. It covers topics like alcohols, carboxylic acids and their derivatives, oxidation and reduction reactions, and C-C bond formation. Each chapter explains different reaction types and transformation pathways. The introduction discusses using natural products for medical treatments historically and the importance of functional group interconversions in organic synthesis.
The document provides an overview of chemical reactions, including:
1) It describes three main types of chemical reactions: substitution reactions, addition reactions, and elimination reactions.
2) It explains that nucleophiles are electron-rich reagents that donate electrons, while electrophiles are electron-poor reagents that accept electrons. Common nucleophiles include anions and molecules with lone pairs, while common electrophiles include protons and elements in Group 13.
3) Using examples, it illustrates how nucleophiles can donate electrons in substitution and addition reactions, and how electrophiles can accept electrons in these reactions.
This document summarizes a study that used X-ray crystallography and resonance Raman spectroscopy to characterize the oxo-molybdenum dithiolene complex (Tp*)MoO(qdt), which is a model system relevant to pyranopterin molybdenum enzyme active sites like sulfite oxidase. The compound was found to crystallize in the triclinic space group P1. Structural parameters of the first coordination sphere were similar to the related complex (Tp*)MoO(bdt), suggesting geometric effects are not major contributors to electronic structural differences between the two complexes. Raman spectroscopy provided evidence the dithiolene ligand interacts with the molybdenum center through
Polymorphism of Acylglycerols: A Stereochemical Perspectiverjcraven
The underlying cause for polymorphism in acyglycerols has puzzled researchers for more than 150 years. For the last 50 years or so, the subcell concept has been used to describe and understand this phenomenon. In general, there is a correlation between the crystal structure of the various polymorphs and the packing of the polymethylene chains (reflected in the subcell). This occurs because, for acylglcyerols, higher-melting polymorphs form due to an increase in packing efficiency for the polymethylene chains (i.e. packing efficiency increases α < β′ < β) . These same concepts are used to understand polymorphism in waxes and alkanes, and when applied to acylglycerols, they work reasonably well (i.e. as a rule of thumb). They are, however, of limited use in understanding more complex or exceptional polymorphic behaviors. In fact, progress in answering more difficult research problems is hindered, rather than helped, by the current reliance on the subcell concept.
In this work we provide a more fundamental understanding for polymorphism in acylglycerols. Using a stereochemical approach, we are able to provide solutions and mechanisms for research questions that have challenged (and remained unanswered) by many previous workers.
1) Chiral phosphoric acid catalyst PA-1 promotes the highly enantioselective ring-opening of meso-aziridines with a variety of functionalized aromatic thiols. The reaction proceeds in good yields and with up to 97% enantiomeric excess.
2) The reaction tolerates a wide range of substituted thiols, including those with electron-donating and -withdrawing groups, as well as heteroaromatic thiols. Alkyl thiols perform less well.
3) Different meso-aziridine substrates are also suitable, including those with fused ring systems or acyclic substituents. The reaction provides a simple method for the
More problems covering asymmetric synthesis. This time with examples of substrate control, chiral reagents, and chiral catalysis. Also another example of a synthesis.
This document summarizes a study on new electrically-driven chiral molecular switches based on axially dissymmetric 1,1'-binaphthyl and electrochromic viologens. The switches (R)-1 and (R)-2 were synthesized and characterized. Their optical properties, including absorption and circular dichroism spectra, changed drastically upon electrochemical redox reaction, demonstrating efficient chiroptical switching. The switches take advantage of the strong chirality of 1,1'-binaphthyl and the electrochromic behavior of viologens to achieve modulation of their chiroptical properties with an electric field.
1992 schottky barrier formation in conducting polymerspmloscholte
1. The authors studied thin films of poly(3-hexylthiophene) (PHT) and polypyrrole (PPY) on highly oriented pyrolytic graphite using scanning tunneling microscopy.
2. They observed semicrystalline order in the form of micro-islands connected by parallel polymer strands. The orientation of the strands is determined by the substrate.
3. For PPY films, they observed superhelical structures not previously reported. The apparent height of polymer strands was found to differ for positive and negative bias voltages, which the authors attribute to the formation of a Schottky barrier between the metallic tip and semiconducting polymer.
This document contains 25 questions assessing knowledge of key concepts in biology including:
1) The structure of DNA and how base substitution mutations can cause diseases like sickle cell anemia.
2) The production of dipeptides via condensation reactions and the role of condensation and hydrolysis in amino acid and dipeptide relationships.
3) Processes of translation, aerobic respiration including oxidative phosphorylation, and effects of temperature, pH and substrate concentration on enzyme activity.
This document reports on a study of the oxygenation properties of hemoglobin from the earthworm Lumbricus terrestris under varying conditions of pH, salts, and temperature. Key findings include:
1) Hemoglobin from L. terrestris exhibits relatively small cooperativity (free energy of 1.6-2.8 kcal/mol) and a large, pH-dependent Hill coefficient that reaches a maximum of 7.9.
2) Cations, not anions, control oxygen binding, with divalent cations having a larger effect than monovalent cations. Effectiveness decreases in the order Ca2+ > Sr2+ > Ba2+ and Mg2+ > Na+.
The document discusses intermolecular forces, which are the attractive forces between molecules. It defines key terms needed to understand intermolecular forces, such as bond dipoles resulting from the unequal sharing of electrons in polar covalent bonds. Molecular properties are influenced by both intramolecular bonds and intermolecular forces. Inductive effects cause polarization of bonds within and between molecules. Electron-withdrawing groups increase molecular polarity through induction, while electron-donating groups decrease polarity. These intermolecular forces, along with molecular shape and polarity, determine critical physical properties like boiling points and solubility.
1. Eleven new secondary metabolites were isolated from the endophytic fungal strain Phomopsis sp. XZ-26 from Camptotheca acuminate, including nine lovastatin analogues (oblongolides N-V and 5-11), one linear furanopolyketide, one monoterpene, and four known compounds.
2. The structures of the new compounds were elucidated using spectroscopic data including NMR, HR-MS, and X-ray crystallography. The new compounds included hydroxylated derivatives of known oblongolides and linear furanopolyketides.
3. The antimicrobial activities of some of the isolated compounds were evaluated but
Retrosynthetic analysis, definition, importance, disconnection approach, one group two group disconnection logical and illogical disconnection approach compounds containing two nitrogen atom retrosynthetic analysis of camphor, cartisone, reserpine
Switching Off and On the Supramolecular Chiral Memory in PorphyrinAngela Mammana
This document summarizes research on switching the chiral memory in porphyrin assemblies on and off. The researchers designed a system using tetra-cationic and tetra-anionic porphyrins that form chiral supramolecular complexes when mixed in the presence of a chiral template, like an amino acid. This complex retains its chirality even after removing the template. The researchers found they could cycle the complex between "written" and "erased" states by turning the electrostatic interactions on and off via protonation/deprotonation. Protonation induces aggregation and chirality, while raising the pH leads to disassembly and loss of chirality, but chiral "seeds" allow reassembly of the
The document describes the isolation and characterization of four new meroterpenoid metabolites, dhilirolides A-D, from cultures of the fungus Penicillium purpurogenum collected in Sri Lanka. Dhilirolides A-D have unprecedented carbon skeletons containing dhilirane or isodhilirane rings. Dhilirolide A was characterized by NMR and X-ray crystallography, confirming its complex structure. Dhilirolides B-D have similar structures to A but differ in oxidation states or positions of double bonds, as elucidated by NMR. The dhilirolides represent a new class of fungal secondary metabolites with potential biomedical applications.
1. The document describes several organic reactions and asks questions about determining product structures and rationalizing stereochemical outcomes.
2. Key concepts discussed include: conformational analysis to determine reactivity; Cram chelation control to set stereochemistry; Ireland-Claisen rearrangements maintaining configuration; and using chiral auxiliaries to induce diastereoselectivity through chelation.
3. Rationalizations of stereochemical outcomes involve analyzing transition states, identifying favored conformations, and determining approach selectivity based on steric interactions.
The document contains a question bank with long essay, short essay and short answer questions related to organic chemistry reactions, mechanisms, and concepts. The long essay questions cover topics such as SN1, SN2, E1, E2 reactions; electrophilic aromatic substitution reactions; carbocation rearrangements; elimination reactions; and more. The short essay questions focus on specific reaction mechanisms and organic chemistry theories. The short answer questions test definitions, IUPAC names, and structural representations.
This document summarizes a study of general trends in the acceptor ability of σ bonds (C-X) where X is a main group element from groups IVa-IIa. The study finds that acceptor ability increases when moving to the end of a period and down a group in monosubstituted ethanes. In monosubstituted ethenes, acceptor ability is more dependent on the electronegativity of the substituent X. C-X bonds can have highly anisotropic stereoelectronic effects, with some bonds being good acceptors at one end but poor at the other. The trends revealed provide a qualitative understanding of stereoelectronic effects, though the magnitude of hyperconjugative
Sandrogreco The Hard Soft Acids Bases (Hsab) Principle And Organic ChemistryProfª Cristiana Passinato
This document summarizes the "hard soft acids bases (HSAB) principle" proposed by Pearson in 1963 to classify and predict chemical reactions. It outlines scales to classify Lewis acids and bases as either "hard" or "soft" based on their size, charge, and polarizability. The HSAB principle states that "hard" acids and bases form stronger bonds with each other, while "soft" acids and bases interact more favorably. This concept can be used to explain and predict the selectivity and stability of compounds, complexes, and reaction outcomes. The document provides examples of how the HSAB principle applies to organic reactions involving alkylation, substitution, addition, and other reaction types.
Pearson's Hard Soft Lewis Acid Base (HSAB) principle classifies Lewis acids and bases as hard, soft or borderline based on their ability to form ionic or covalent complexes. According to the principle, hard acids prefer hard bases and form ionic complexes, while soft acids prefer soft bases and form covalent complexes. However, the HSAB model oversimplifies reactions and introduces ambiguities, as no single physical parameter determines hardness. A more nuanced analysis is needed to understand complex Lewis acid-base interactions.
The document discusses Pearson's Hard and Soft Acid and Base (HSAB) theory, which states that hard acids prefer to bond with hard bases and soft acids prefer to bond with soft bases. It provides examples of hard and soft ligands and metal ions. Key points include:
- Hard metals have high charge, small size, and are not easily polarized, while soft metals are the opposite.
- The theory can be used to explain the bonding preferences of ambidentate ligands like thiocyanate based on whether they bond to hard or soft metals through nitrogen or sulfur.
- The theory has applications in explaining reactivity patterns in inorganic reactions, organic reactions involving acids and bases of different hardness, and precipitation reactions.
The document discusses the hard and soft acid and base (HSAB) theory introduced by Pearson in 1963. It explains that hard acids prefer to coordinate with hard bases, and soft acids prefer soft bases, due to their relative polarizabilities. Hard acids and bases are less polarizable, while soft species are more polarizable and form stronger bonds through electron sharing. The HSAB concept is used to understand stability, reactions, and reaction mechanisms based on qualitative descriptions of predominant factors like polarizability.
The document discusses pericyclic reactions and the Woodward-Hoffmann rules for predicting their stereochemistry. It begins by defining pericyclic reactions as concerted reactions where bonds are formed or broken in a cyclic transition state. It then provides examples of different types of pericyclic reactions, including electrocyclizations, cycloadditions, and sigmatropic rearrangements. The Woodward-Hoffmann theory is explained, showing how it can be used to predict whether a reaction will proceed with antarafacial conrotation or suprafacial disrotation based on whether the reaction is thermally or photochemically induced. Specific examples like cyclobutene formation and the Diels-Alder reaction are analyzed in
This document provides an overview of a university course on organic synthesis. It covers topics like pericyclic reactions, electrocyclizations, sigmatropic rearrangements, and the Woodward-Hoffmann rules for predicting stereochemistry. Examples are given of reaction mechanisms and how the rules explain stereochemical outcomes. The document also lists additional reading materials and notes that attending all lectures is essential since not all material is covered in the handout.
Photosynthesis is a complex, multistep process that was largely elucidated by the mid-20th century through experiments measuring photosynthetic efficiency, identifying reaction center pigments, proposing the Z-scheme of electron transport, discovering the Calvin cycle, and identifying Rubisco as the key enzyme. While historically photosynthesis research was isolated from other fields, it is now recognized that photosynthesis is closely related to other cellular processes through reactive oxygen species, redox regulation, and chloroplast signals, and plays an important role in plant stress responses, productivity, and global climate modeling. This special issue explores new concepts and unanswered questions in photosynthesis research using modern techniques.
This document provides an overview of pericyclic reactions, including:
1. It classifies pericyclic reactions into four main categories: electrocyclic reactions, cycloaddition reactions, sigmatropic rearrangements, and ene reactions.
2. It discusses the Woodward-Hoffmann rules for determining the stereochemistry of pericyclic reactions under thermal and photochemical conditions.
3. It provides examples of specific pericyclic reactions, such as the Diels-Alder reaction and sigmatropic shifts, analyzing the frontier molecular orbitals involved.
1. The study examined the organization of photosystem complexes in various cyanobacteria, a glaucocystophyte, and a primitive rhodophyte using blue-native polyacrylamide gel electrophoresis (BN-PAGE).
2. In contrast to known cyanobacteria that form PSI trimers, the filamentous cyanobacterium Anabaena sp. PCC 7120 and the glaucocystophyte Cyanophora paradoxa were found to have PSI tetramers and dimers but no trimers.
3. The primitive rhodophyte Cyanidioschyzon merolae had two species of monomeric PSI complexes with different light-harvesting chlorophyll compositions
1) The document discusses light-dependent (photosynthetic) generators of proton potential, specifically focusing on the photosynthetic apparatus of purple bacteria.
2) Photosynthesis in purple bacteria involves a light-dependent cyclic redox chain where absorption of light by bacteriochlorophyll leads to electron transfer across the membrane, generating a proton gradient.
3) Key components of the redox chain include bacteriochlorophyll dimer and monomer, bacteriopheophytin, ubiquinone, cytochromes, and a nonheme iron-sulfur protein that facilitate electron transfer and proton pumping across the membrane.
This document contains 25 questions assessing knowledge of key concepts in biology including:
1) The structure of DNA and how base substitution mutations can cause diseases like sickle cell anemia.
2) The production of dipeptides via condensation reactions and the role of condensation and hydrolysis in amino acid and dipeptide relationships.
3) Processes of translation, aerobic respiration including oxidative phosphorylation, and effects of temperature, pH and substrate concentration on enzyme activity.
This document reports on a study of the oxygenation properties of hemoglobin from the earthworm Lumbricus terrestris under varying conditions of pH, salts, and temperature. Key findings include:
1) Hemoglobin from L. terrestris exhibits relatively small cooperativity (free energy of 1.6-2.8 kcal/mol) and a large, pH-dependent Hill coefficient that reaches a maximum of 7.9.
2) Cations, not anions, control oxygen binding, with divalent cations having a larger effect than monovalent cations. Effectiveness decreases in the order Ca2+ > Sr2+ > Ba2+ and Mg2+ > Na+.
The document discusses intermolecular forces, which are the attractive forces between molecules. It defines key terms needed to understand intermolecular forces, such as bond dipoles resulting from the unequal sharing of electrons in polar covalent bonds. Molecular properties are influenced by both intramolecular bonds and intermolecular forces. Inductive effects cause polarization of bonds within and between molecules. Electron-withdrawing groups increase molecular polarity through induction, while electron-donating groups decrease polarity. These intermolecular forces, along with molecular shape and polarity, determine critical physical properties like boiling points and solubility.
1. Eleven new secondary metabolites were isolated from the endophytic fungal strain Phomopsis sp. XZ-26 from Camptotheca acuminate, including nine lovastatin analogues (oblongolides N-V and 5-11), one linear furanopolyketide, one monoterpene, and four known compounds.
2. The structures of the new compounds were elucidated using spectroscopic data including NMR, HR-MS, and X-ray crystallography. The new compounds included hydroxylated derivatives of known oblongolides and linear furanopolyketides.
3. The antimicrobial activities of some of the isolated compounds were evaluated but
Retrosynthetic analysis, definition, importance, disconnection approach, one group two group disconnection logical and illogical disconnection approach compounds containing two nitrogen atom retrosynthetic analysis of camphor, cartisone, reserpine
Switching Off and On the Supramolecular Chiral Memory in PorphyrinAngela Mammana
This document summarizes research on switching the chiral memory in porphyrin assemblies on and off. The researchers designed a system using tetra-cationic and tetra-anionic porphyrins that form chiral supramolecular complexes when mixed in the presence of a chiral template, like an amino acid. This complex retains its chirality even after removing the template. The researchers found they could cycle the complex between "written" and "erased" states by turning the electrostatic interactions on and off via protonation/deprotonation. Protonation induces aggregation and chirality, while raising the pH leads to disassembly and loss of chirality, but chiral "seeds" allow reassembly of the
The document describes the isolation and characterization of four new meroterpenoid metabolites, dhilirolides A-D, from cultures of the fungus Penicillium purpurogenum collected in Sri Lanka. Dhilirolides A-D have unprecedented carbon skeletons containing dhilirane or isodhilirane rings. Dhilirolide A was characterized by NMR and X-ray crystallography, confirming its complex structure. Dhilirolides B-D have similar structures to A but differ in oxidation states or positions of double bonds, as elucidated by NMR. The dhilirolides represent a new class of fungal secondary metabolites with potential biomedical applications.
1. The document describes several organic reactions and asks questions about determining product structures and rationalizing stereochemical outcomes.
2. Key concepts discussed include: conformational analysis to determine reactivity; Cram chelation control to set stereochemistry; Ireland-Claisen rearrangements maintaining configuration; and using chiral auxiliaries to induce diastereoselectivity through chelation.
3. Rationalizations of stereochemical outcomes involve analyzing transition states, identifying favored conformations, and determining approach selectivity based on steric interactions.
The document contains a question bank with long essay, short essay and short answer questions related to organic chemistry reactions, mechanisms, and concepts. The long essay questions cover topics such as SN1, SN2, E1, E2 reactions; electrophilic aromatic substitution reactions; carbocation rearrangements; elimination reactions; and more. The short essay questions focus on specific reaction mechanisms and organic chemistry theories. The short answer questions test definitions, IUPAC names, and structural representations.
This document summarizes a study of general trends in the acceptor ability of σ bonds (C-X) where X is a main group element from groups IVa-IIa. The study finds that acceptor ability increases when moving to the end of a period and down a group in monosubstituted ethanes. In monosubstituted ethenes, acceptor ability is more dependent on the electronegativity of the substituent X. C-X bonds can have highly anisotropic stereoelectronic effects, with some bonds being good acceptors at one end but poor at the other. The trends revealed provide a qualitative understanding of stereoelectronic effects, though the magnitude of hyperconjugative
Sandrogreco The Hard Soft Acids Bases (Hsab) Principle And Organic ChemistryProfª Cristiana Passinato
This document summarizes the "hard soft acids bases (HSAB) principle" proposed by Pearson in 1963 to classify and predict chemical reactions. It outlines scales to classify Lewis acids and bases as either "hard" or "soft" based on their size, charge, and polarizability. The HSAB principle states that "hard" acids and bases form stronger bonds with each other, while "soft" acids and bases interact more favorably. This concept can be used to explain and predict the selectivity and stability of compounds, complexes, and reaction outcomes. The document provides examples of how the HSAB principle applies to organic reactions involving alkylation, substitution, addition, and other reaction types.
Pearson's Hard Soft Lewis Acid Base (HSAB) principle classifies Lewis acids and bases as hard, soft or borderline based on their ability to form ionic or covalent complexes. According to the principle, hard acids prefer hard bases and form ionic complexes, while soft acids prefer soft bases and form covalent complexes. However, the HSAB model oversimplifies reactions and introduces ambiguities, as no single physical parameter determines hardness. A more nuanced analysis is needed to understand complex Lewis acid-base interactions.
The document discusses Pearson's Hard and Soft Acid and Base (HSAB) theory, which states that hard acids prefer to bond with hard bases and soft acids prefer to bond with soft bases. It provides examples of hard and soft ligands and metal ions. Key points include:
- Hard metals have high charge, small size, and are not easily polarized, while soft metals are the opposite.
- The theory can be used to explain the bonding preferences of ambidentate ligands like thiocyanate based on whether they bond to hard or soft metals through nitrogen or sulfur.
- The theory has applications in explaining reactivity patterns in inorganic reactions, organic reactions involving acids and bases of different hardness, and precipitation reactions.
The document discusses the hard and soft acid and base (HSAB) theory introduced by Pearson in 1963. It explains that hard acids prefer to coordinate with hard bases, and soft acids prefer soft bases, due to their relative polarizabilities. Hard acids and bases are less polarizable, while soft species are more polarizable and form stronger bonds through electron sharing. The HSAB concept is used to understand stability, reactions, and reaction mechanisms based on qualitative descriptions of predominant factors like polarizability.
The document discusses pericyclic reactions and the Woodward-Hoffmann rules for predicting their stereochemistry. It begins by defining pericyclic reactions as concerted reactions where bonds are formed or broken in a cyclic transition state. It then provides examples of different types of pericyclic reactions, including electrocyclizations, cycloadditions, and sigmatropic rearrangements. The Woodward-Hoffmann theory is explained, showing how it can be used to predict whether a reaction will proceed with antarafacial conrotation or suprafacial disrotation based on whether the reaction is thermally or photochemically induced. Specific examples like cyclobutene formation and the Diels-Alder reaction are analyzed in
This document provides an overview of a university course on organic synthesis. It covers topics like pericyclic reactions, electrocyclizations, sigmatropic rearrangements, and the Woodward-Hoffmann rules for predicting stereochemistry. Examples are given of reaction mechanisms and how the rules explain stereochemical outcomes. The document also lists additional reading materials and notes that attending all lectures is essential since not all material is covered in the handout.
Photosynthesis is a complex, multistep process that was largely elucidated by the mid-20th century through experiments measuring photosynthetic efficiency, identifying reaction center pigments, proposing the Z-scheme of electron transport, discovering the Calvin cycle, and identifying Rubisco as the key enzyme. While historically photosynthesis research was isolated from other fields, it is now recognized that photosynthesis is closely related to other cellular processes through reactive oxygen species, redox regulation, and chloroplast signals, and plays an important role in plant stress responses, productivity, and global climate modeling. This special issue explores new concepts and unanswered questions in photosynthesis research using modern techniques.
This document provides an overview of pericyclic reactions, including:
1. It classifies pericyclic reactions into four main categories: electrocyclic reactions, cycloaddition reactions, sigmatropic rearrangements, and ene reactions.
2. It discusses the Woodward-Hoffmann rules for determining the stereochemistry of pericyclic reactions under thermal and photochemical conditions.
3. It provides examples of specific pericyclic reactions, such as the Diels-Alder reaction and sigmatropic shifts, analyzing the frontier molecular orbitals involved.
1. The study examined the organization of photosystem complexes in various cyanobacteria, a glaucocystophyte, and a primitive rhodophyte using blue-native polyacrylamide gel electrophoresis (BN-PAGE).
2. In contrast to known cyanobacteria that form PSI trimers, the filamentous cyanobacterium Anabaena sp. PCC 7120 and the glaucocystophyte Cyanophora paradoxa were found to have PSI tetramers and dimers but no trimers.
3. The primitive rhodophyte Cyanidioschyzon merolae had two species of monomeric PSI complexes with different light-harvesting chlorophyll compositions
1) The document discusses light-dependent (photosynthetic) generators of proton potential, specifically focusing on the photosynthetic apparatus of purple bacteria.
2) Photosynthesis in purple bacteria involves a light-dependent cyclic redox chain where absorption of light by bacteriochlorophyll leads to electron transfer across the membrane, generating a proton gradient.
3) Key components of the redox chain include bacteriochlorophyll dimer and monomer, bacteriopheophytin, ubiquinone, cytochromes, and a nonheme iron-sulfur protein that facilitate electron transfer and proton pumping across the membrane.
1) The document discusses light-dependent (photosynthetic) generators of proton potential, specifically focusing on the photosynthetic apparatus of purple bacteria.
2) Photosynthesis in purple bacteria involves a light-dependent cyclic redox chain where absorption of light by bacteriochlorophyll leads to electron transfer across the membrane, generating a proton gradient.
3) Key components of the redox chain include bacteriochlorophyll dimer and monomer, bacteriopheophytin, ubiquinone, cytochromes, and a nonheme iron-sulfur protein that facilitate electron transfer and proton pumping across the membrane.
Reduction of cu o and cu2o with h2 h embedding and kinetics effects in the ...Luciana Pirone
This document summarizes a study that used time-resolved X-ray diffraction, X-ray absorption fine structure spectroscopy, and density functional theory calculations to investigate the reduction of CuO and Cu2O with hydrogen gas. The main findings were:
1) CuO reduces directly to metallic copper without forming intermediate copper suboxides like Cu4O3 or Cu2O under normal hydrogen flow rates.
2) The reduction of CuO is easier than the reduction of Cu2O, with apparent activation energies of 14.5 kcal/mol and 27.4 kcal/mol, respectively.
3) During CuO reduction, the system can reach metastable states and react with hydrogen instead of
Deciphering reaction mechanism with intermediate trappingDaniel Morton
This module provides an overview of a tool used to gain information on a reaction mechanism; reactive intermediate trapping.
A reactive intermediate is a short-lived, high-energy, highly reactive molecule. When generated in a chemical reaction, it will quickly convert into a more stable molecule. When their existence is indicated, reactive intermediates can help explain how a chemical reaction takes place.
Contributed by:
Shuangyu Ma & Yiling Bi (Undergraduate Students)
University of Utah
2014
This document provides an overview of molecular variation in homologous series and isosteric replacements for medicinal chemistry. It discusses different types of molecular variations such as variations based on homologous series with different biological response curves. It also discusses isosteric replacements, including the history and development of isosterism concepts. Current isosteric and bioisosteric modifications are presented. The document also discusses molecular variations based on ring transformations, homodimer and heterodimer ligands using the twin drug approach, and molecular variations in medicinal chemistry applications.
1. This document outlines the key objectives and concepts around photosynthesis. It discusses the process of photosynthesis including the light reactions where ATP and NADPH are produced and the Calvin cycle where carbon is fixed into organic compounds.
2. It describes the structures involved like chloroplasts and their membranes as well as the components of the photosystems. The movement of electrons during cyclic and noncyclic electron flow is also outlined.
3. Finally, it discusses topics like chemiosmosis in chloroplasts versus mitochondria, the role of ATP and NADPH in the Calvin cycle, and consequences of photorespiration which provides evolutionary context.
This document reports the first detection of hydrogen peroxide (HOOH) in interstellar space. Four HOOH transitions were detected toward the ρ Oph A molecular cloud core, including three transitions mapped over the densest part of the core. Analysis of the line intensities using a rotation diagram method derived a HOOH rotation temperature of 22 K and column density of 8×1012 cm-2, corresponding to an abundance relative to H2 of about 1×10-10. This detection provides evidence that HOOH plays a role in oxygen and water chemistry in molecular clouds.
The document summarizes the Dienone-Phenol rearrangement reaction. It begins by classifying rearrangement reactions based on the migrating group or atom. It then provides examples of the Dienone-Phenol rearrangement where disubstituted cyclohexadienones rearrange to the corresponding disubstituted phenols. The mechanism involves the generation of a carbocation through protonation, followed by rearrangement and loss of a proton to form the phenol product. The rearrangement is driven by aromatization. It notes applications in synthesizing anthracenes, phenanthrenes, and steroids like santonin. References on reaction mechanisms and rearrangements are also provided.
Studies on Stomatal Movement in Dolichus biflorus Linn. (Fabaceae)ijtsrd
Usually relative turgor changes which maintain osmotic gradients in the guard cells cause stomatal movements. In many species the dominant participation of K+ in stomatal movements was well established. Organic acids such as malate, citrate, glutamate and aspertate were reported to serve as counter ions of K+ in many species. Both oxidative phosphorylation and photo phosphorylation are potential energy sources. In earlier studies, the functional role of PS II were not clearly understood. Hence the present study is aimed to understand the role of PS II in guard cells of Dolicus biflorus Linn. a Fabaceae member. Influence of PS II electron acceptors and donors such as potassium ferricyanide, hydroxylamine hydrochloride, MnCl2, Sodium ascorbate, diphenyl carbazide, ATP, ADP, ATP + MnCl2 and ADP + MnCl2, MnCl2 + NADP and Hydroxylamine hydrochloride + NADP is studied to understand the role of photo system II on stomatal movements. Dr.G.Meerabai | B.Koteswari"Studies on Stomatal Movement in Dolichus biflorus Linn. (Fabaceae)" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-1 | Issue-6 , October 2017, URL: http://www.ijtsrd.com/papers/ijtsrd2528.pdf http://www.ijtsrd.com/biological-science/botany/2528/studies-on-stomatal-movement-in--dolichus-biflorus-linn-fabaceae/drgmeerabai-
The document discusses developing novel fluorescent dyes through asymmetric boron difluoride complexes. It aims to design dyes with broad Stokes shifts like BODIPY but without its narrow emission properties. Future work discussed includes synthesizing BF2 complexes with N,O and N,N ligands to study the effect of heteroatomic substitution on emission. Distyryl and arylbenzamide BF2 complexes will also be made to investigate conjugation extension and solid state quenching effects. The overall goal is tunable dyes for applications like bioimaging, sensors and light emitting devices.
1) TADF molecules are designed with electron donating and withdrawing groups to suppress geometrical change and lower reorganization energy between singlet and triplet states. This increases intersystem crossing rate and enables near 100% fluorescence.
2) Cyano groups as electron withdrawing groups suppress geometrical change in the excited state. Carbazole groups as electron donating groups break molecular symmetry and separate electron densities of highest occupied and lowest unoccupied orbitals.
3) Twisted molecular geometry separates electron densities and lowers reorganization energy, increasing intersystem crossing rate and reverse intersystem crossing rate for delayed fluorescence.
Bacteria LENRs-and isotopic shifts in Uranium-Larsen-Lattice Energy Dec 7 2010Lewis Larsen
The attached paper provides a description of a theoretical W-L LENR Actinide nucleosynthetic network and selected examples of published mainstream, peer-reviewed experimental data which provide evidence that this network may well be operating in a variety of different environments on earth --- hidden in plain sight. In particular, we show how some or all of the Actinide network pathways could potentially be present in soils, ocean sediments, dusty chemical explosions, volcanic eruptions, and extraterrestrial impact events.
The document describes several reactions involving conjugate additions and discusses the stereochemical outcomes. It rationalizes the stereoselectivity using concepts like chair conformations, Felkin-Anh control, and Cram chelation control. By analyzing the transition states and preferred conformations, it is able to explain why the reactions favor one stereoisomer over another in each case.
A Suspected Derivative Morphology for pheophytin (脫鎂葉綠素) and the Enhanced H...cclarbl
The document discusses a conjectured derivative morphology of pheophytin that could facilitate proton conduction and hydrogen decomposition. Quantum simulations showed the derivative structure was energetically favorable. Spectral analyses of extracted pheophytin matched the simulated derivative structure more than the textbook structure. Battery experiments demonstrated pheophytin-catalyzed electrodes produced more discharge than non-catalyzed electrodes, providing evidence pheophytin can catalyze hydrogen decomposition. The findings suggest a derivative pheophytin form may exist that could better explain experimental observations than the accepted textbook structure.
Similar to Sandrogreco Fukui Fmo Accts Chem Res 1971[1] (20)
Poema inspirado no filme "Borboletas Negras" sobre Ingrid Jonker, poetiza sul-africana do tempo do Apartheid, citada em discurso histórico de Nelson Mandela.
O documento discute a produção de iogurte através da fermentação láctica por cultivos de bactérias como Streptococcus thermophilus e Lactobacillus bulgaricus. O processo envolve o tratamento térmico do leite, resfriamento e adição dos fermentos láticos para iniciar a fermentação a 45°C por 5 horas, resultando na conversão da lactose em ácido lático. O iogurte produzido contém probióticos que promovem benefícios à saúde.
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Um pai bateu violentamente no seu filho de 3 anos depois que a criança desenhou nos estofos do novo carro da família com um marcador. A criança teve que ter as mãos amputadas devido aos ferimentos graves e, ao ver o filho no hospital, o pai suicidou-se com remorso. O documento reflete sobre dar importância excessiva a bens materiais em detrimento do amor pela família.
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1) A partir de janeiro de 2008, Brasil, Portugal e outros países lusófonos concordaram em unificar a ortografia do português, porém até abril de 2008 nenhuma mudança havia ocorrido ainda.
2) As principais mudanças seriam a remoção do acento circunflexo em palavras terminadas em "o" duplo e novas regras para o uso do hífen.
3) A unificação ortográfica facilitaria a divulgação da língua e eventos internacionais, além de exames
Este documento fornece orientações para a elaboração de apresentações de slides para videoconferências, incluindo a adoção de um modelo padrão, uso de fontes, cores e tamanhos específicos, otimização dos espaços dos slides e envio antecipado dos arquivos para teste.
Este documento presenta una introducción al libro Humano, demasiado humano de Nietzsche. Describe el proceso de desprendimiento que experimenta un espíritu para convertirse en un "espíritu libre". Comienza con la necesidad de inventar figuras como los "espíritus libres" para acompañar a Nietzsche en su soledad. Luego explica cómo un espíritu atado puede liberarse súbitamente a través de un terremoto interior que le hace desear alejarse de lo que amaba. Finalmente, tras años
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2) A teoria estrutural de Kekulé explica as características do átomo de carbono que permitem a formação de cadeias carbônicas através de ligações simples e múltiplas.
3) Há diferentes tipos de classificação para cadeias carbônicas, inclu
O documento apresenta o gabarito de uma lista de exercícios de Química Orgânica sobre estrutura e reatividade de compostos orgânicos. As questões abordam tópicos como efeitos estereoeletrônicos, aromatidade, estabilidade de estruturas ressonantes e fatores que influenciam a acidez de ácidos. As respostas explicam os conceitos por meio de diagramas de orbitais moleculares e hibridização.
O documento apresenta uma parábola sobre um jovem que compra um livro ensinando a pilotar um avião em sete lições fáceis. Ele segue as instruções e consegue voar, mas quando precisa pousar, descobre que as instruções para pousar estão no segundo volume, que ele não comprou. Da mesma forma, a Igreja tem riqueza teológica, mas precisa encontrar formas simples de transmiti-la ao povo, como a utilização de parábolas, tema do documento.
- O documento discute a educação a distância por videoconferência, definindo os termos, descrevendo os tipos de transmissão e salas de videoconferência, e analisando as vantagens e desvantagens desse método para a educação.
1. The document is the periodic table of elements listing all 118 known elements by their atomic number, symbol, name, and atomic weight.
2. The periodic table is organized into blocks by the metallic and non-metallic properties of elements and arranged by increasing atomic number.
3. Elements are also classified as metals, metalloids, and nonmetals according to their general physical and chemical properties.
1. The document provides the standard periodic table of the elements with atomic numbers 1-103 arranged in the standard layout.
2. It includes the element name, symbol, atomic number, atomic mass, and key for each element.
3. Additional notes are provided on standard atomic weights and uncertainties, as well as elements beyond atomic number 112 that have been reported but not fully authenticated.
1. The document is the IUPAC Periodic Table of the Elements listing all 118 known elements by their atomic number, symbol, name, and standard atomic weight.
2. Key information provided for each element includes the atomic number, element name, chemical symbol, and IUPAC 2001 standard atomic weight with associated uncertainty.
3. Elements without stable nuclides list the mass number of the longest-lived isotope instead of atomic weight. Elements above 112 have been reported but not fully authenticated.
O documento descreve a evolução do modelo atômico ao longo do tempo, desde as primeiras ideias de Dalton e Avogadro até o modelo planetário de Rutherford e finalmente o modelo quântico de Bohr. Destaca os principais contribuidores como Thomson, Maxwell, Planck e Bohr e como cada um foi importante para o desenvolvimento da compreensão moderna da estrutura atômica.
O documento discute a energia nuclear, mencionando os bombardeios atômicos de Hiroshima e Nagasaki no Japão durante a Segunda Guerra Mundial. Explica que a radioatividade ocorre quando núcleos instáveis emitem partículas, podendo ser por emissão alfa, beta ou gama. A taxa de decaimento de materiais radioativos segue uma lei exponencial, onde a meia-vida caracteriza cada isótopo nuclear.
Cerca de 110 crocodilos em perigo crítico de extinção foram encontrados mortos na Índia em apenas 3 meses, vítimas da poluição dos rios onde viviam. A espécie de crocodilo gavial, que existe há 200 milhões de anos, depende exclusivamente de peixes para se alimentar e não consegue escapar da poluição migrando para regiões mais limpas. A baixa temperatura do inverno também pode ter contribuído para o envenenamento dos animais, diminuindo a taxa com que eles eliminavam as substâncias
Driving Business Innovation: Latest Generative AI Advancements & Success StorySafe Software
Are you ready to revolutionize how you handle data? Join us for a webinar where we’ll bring you up to speed with the latest advancements in Generative AI technology and discover how leveraging FME with tools from giants like Google Gemini, Amazon, and Microsoft OpenAI can supercharge your workflow efficiency.
During the hour, we’ll take you through:
Guest Speaker Segment with Hannah Barrington: Dive into the world of dynamic real estate marketing with Hannah, the Marketing Manager at Workspace Group. Hear firsthand how their team generates engaging descriptions for thousands of office units by integrating diverse data sources—from PDF floorplans to web pages—using FME transformers, like OpenAIVisionConnector and AnthropicVisionConnector. This use case will show you how GenAI can streamline content creation for marketing across the board.
Ollama Use Case: Learn how Scenario Specialist Dmitri Bagh has utilized Ollama within FME to input data, create custom models, and enhance security protocols. This segment will include demos to illustrate the full capabilities of FME in AI-driven processes.
Custom AI Models: Discover how to leverage FME to build personalized AI models using your data. Whether it’s populating a model with local data for added security or integrating public AI tools, find out how FME facilitates a versatile and secure approach to AI.
We’ll wrap up with a live Q&A session where you can engage with our experts on your specific use cases, and learn more about optimizing your data workflows with AI.
This webinar is ideal for professionals seeking to harness the power of AI within their data management systems while ensuring high levels of customization and security. Whether you're a novice or an expert, gain actionable insights and strategies to elevate your data processes. Join us to see how FME and AI can revolutionize how you work with data!
In the rapidly evolving landscape of technologies, XML continues to play a vital role in structuring, storing, and transporting data across diverse systems. The recent advancements in artificial intelligence (AI) present new methodologies for enhancing XML development workflows, introducing efficiency, automation, and intelligent capabilities. This presentation will outline the scope and perspective of utilizing AI in XML development. The potential benefits and the possible pitfalls will be highlighted, providing a balanced view of the subject.
We will explore the capabilities of AI in understanding XML markup languages and autonomously creating structured XML content. Additionally, we will examine the capacity of AI to enrich plain text with appropriate XML markup. Practical examples and methodological guidelines will be provided to elucidate how AI can be effectively prompted to interpret and generate accurate XML markup.
Further emphasis will be placed on the role of AI in developing XSLT, or schemas such as XSD and Schematron. We will address the techniques and strategies adopted to create prompts for generating code, explaining code, or refactoring the code, and the results achieved.
The discussion will extend to how AI can be used to transform XML content. In particular, the focus will be on the use of AI XPath extension functions in XSLT, Schematron, Schematron Quick Fixes, or for XML content refactoring.
The presentation aims to deliver a comprehensive overview of AI usage in XML development, providing attendees with the necessary knowledge to make informed decisions. Whether you’re at the early stages of adopting AI or considering integrating it in advanced XML development, this presentation will cover all levels of expertise.
By highlighting the potential advantages and challenges of integrating AI with XML development tools and languages, the presentation seeks to inspire thoughtful conversation around the future of XML development. We’ll not only delve into the technical aspects of AI-powered XML development but also discuss practical implications and possible future directions.
Introduction of Cybersecurity with OSS at Code Europe 2024Hiroshi SHIBATA
I develop the Ruby programming language, RubyGems, and Bundler, which are package managers for Ruby. Today, I will introduce how to enhance the security of your application using open-source software (OSS) examples from Ruby and RubyGems.
The first topic is CVE (Common Vulnerabilities and Exposures). I have published CVEs many times. But what exactly is a CVE? I'll provide a basic understanding of CVEs and explain how to detect and handle vulnerabilities in OSS.
Next, let's discuss package managers. Package managers play a critical role in the OSS ecosystem. I'll explain how to manage library dependencies in your application.
I'll share insights into how the Ruby and RubyGems core team works to keep our ecosystem safe. By the end of this talk, you'll have a better understanding of how to safeguard your code.
HCL Notes und Domino Lizenzkostenreduzierung in der Welt von DLAUpanagenda
Webinar Recording: https://www.panagenda.com/webinars/hcl-notes-und-domino-lizenzkostenreduzierung-in-der-welt-von-dlau/
DLAU und die Lizenzen nach dem CCB- und CCX-Modell sind für viele in der HCL-Community seit letztem Jahr ein heißes Thema. Als Notes- oder Domino-Kunde haben Sie vielleicht mit unerwartet hohen Benutzerzahlen und Lizenzgebühren zu kämpfen. Sie fragen sich vielleicht, wie diese neue Art der Lizenzierung funktioniert und welchen Nutzen sie Ihnen bringt. Vor allem wollen Sie sicherlich Ihr Budget einhalten und Kosten sparen, wo immer möglich. Das verstehen wir und wir möchten Ihnen dabei helfen!
Wir erklären Ihnen, wie Sie häufige Konfigurationsprobleme lösen können, die dazu führen können, dass mehr Benutzer gezählt werden als nötig, und wie Sie überflüssige oder ungenutzte Konten identifizieren und entfernen können, um Geld zu sparen. Es gibt auch einige Ansätze, die zu unnötigen Ausgaben führen können, z. B. wenn ein Personendokument anstelle eines Mail-Ins für geteilte Mailboxen verwendet wird. Wir zeigen Ihnen solche Fälle und deren Lösungen. Und natürlich erklären wir Ihnen das neue Lizenzmodell.
Nehmen Sie an diesem Webinar teil, bei dem HCL-Ambassador Marc Thomas und Gastredner Franz Walder Ihnen diese neue Welt näherbringen. Es vermittelt Ihnen die Tools und das Know-how, um den Überblick zu bewahren. Sie werden in der Lage sein, Ihre Kosten durch eine optimierte Domino-Konfiguration zu reduzieren und auch in Zukunft gering zu halten.
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See how organizational priorities and strategic approaches to data security and privacy are evolving around the globe.
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ABSTRACT: A prima vista, un mattoncino Lego e la backdoor XZ potrebbero avere in comune il fatto di essere entrambi blocchi di costruzione, o dipendenze di progetti creativi e software. La realtà è che un mattoncino Lego e il caso della backdoor XZ hanno molto di più di tutto ciò in comune.
Partecipate alla presentazione per immergervi in una storia di interoperabilità, standard e formati aperti, per poi discutere del ruolo importante che i contributori hanno in una comunità open source sostenibile.
BIO: Sostenitrice del software libero e dei formati standard e aperti. È stata un membro attivo dei progetti Fedora e openSUSE e ha co-fondato l'Associazione LibreItalia dove è stata coinvolta in diversi eventi, migrazioni e formazione relativi a LibreOffice. In precedenza ha lavorato a migrazioni e corsi di formazione su LibreOffice per diverse amministrazioni pubbliche e privati. Da gennaio 2020 lavora in SUSE come Software Release Engineer per Uyuni e SUSE Manager e quando non segue la sua passione per i computer e per Geeko coltiva la sua curiosità per l'astronomia (da cui deriva il suo nickname deneb_alpha).
1. February 1971 STEREOCHEMICAL BY ORBITAL
PATHS INTERACTION 57
trans-benzalacetophenone (64). The anticipated 2,3- alacetophenone. The low bond dissociation energy of
and 2,4-diphenylthiophenes were not detected in the the C-S bond appears to be the major factor responsible
reaction mixture. This result indicates that the photo- for the difference in photochemistry of the two hetero-
cyclic systems.
p~-
cs
~
H
CBHSyO I The foregoing examples have been considered in
hu order to provide at least a partial indication of the
intriguing and unusual transformations that small-
63 ring ketones undergo upon electronic excitation. Con-
C$I,COCH=CHC&, + [CHp=S]x siderable work in this area has been carried out by many
64 investigators, and it may be safely anticipated that
significant and new findings in small-ring photochem-
chemistry of the thietane system proceeds by an en-
istry will be forthcoming in the future.
tirely different path from that encountered in the
azetidine series. The formation of cis- and trans-
It i s a pleasure to acknowledge the vital contribution of my co-
benzalacetophenone may be envisaged as proceeding
workers, whose names are to be found in the references. I wish also
by way of a homolytic cleavage of the benzylic carbon- to express m y thanks to the National Science Foundation, the U . S .
sulfur bond. The resulting diradical undergoes sub- Public Health Service, and the Alfred P. Sloan Foundation for their
sequent fragmentation to thioformaldehyde and benz- financial support.
Recognition of Stereochemical Paths by Orbital Interaction
KENICHI
FUKUI’
Department of Chemistry, Illinois Institute of Technology, Chicago, Illinois 60616
Received August S, 1970
The importance of orbital interactions, particularly The scheme of the HORIO-LUMO interaction be-
between the HO (highest occupied) &;IO (molecular tween reacting species2-* has drawn the attention of
orbital) of one reactant and the LU (lowest unoccupied) organic chemists to the interpretation of the steric
110 of the other, in rationalizing chemical reactions is course of concerted processes, mainly through the
now invincibly e ~ i d e n t . ~Several papers have dis-
,~ elegant generalization of stereoselection rules and the
cussed this problem, giving a fair reasoning of the or- classification of various stereospecific reactions by
bital interaction ~ c h e m e . ~ The physical grounds for
-~ Woodward and H ~ f f m a n n . ~Although a large part of
differentiation of the HOMO and LUMO from the other their interpretation is based on the correlation diagram
MO’s have also been disclosed.’ method, the orbital interaction scheme is also used in
some parts, namely, in the explanation of the preferable
paths of ring opening for cyclobutenes and for cyclo-
(1) Address correspondence to: Department of Hydrocarbon propyl derivatives, the dimerization of two ethylene
Chemistry, Kyoto University, Kyoto, Japan. molecules by an orthogonal approach, the migration of
(2) For instance, see K. Fukui, “Molecular Orbitals in Chemistry,
Physics, and Biology,” P.-0. Lowdin and B. Pullman, Ed., Academic hydrogen or alkyl across a conjugated chain, the exo-
Press, New York, N . Y., 1964, p 513, and references cited therein, and endo selectivity in Diels-Alder-type cycloadditions, and
subsequent papers on the frontier electron theory.
(3). (a) K. Fukui, Bull. Chem. SOC. Jap., 39, 498 (1966); (b) K. the addition of ketenes to olefins. Obviously the cor-
Fukui and H. Fujimoto, ibid., 39, 2116 (1966); (c) K. Fukui and H. relation diagram criteria are not employed in some cases,
Fujimoto, “Mechanisms of Molecular Migrations,” Vol. 2, B. S.
Thyagarajan, Ed., Interscience, New York, N. Y., 1969, p 118; (d) such as interpretation of “sigmatropic” reactions, in
K. Fukui, “Theory of Orientation and Stereoselection,” Springer- which the reaction path has no usable symmetric
Verlag, Heidelberg, 1970.
(4) (a) G. Klopman and R. F. Hudson, Theor. Chim. Acta, 8, character.
165 (1967); (b) R. F. Hudson and G. Klopman, Tetrahedron Lett., The purpose of this Account is to show that the
1103 (1967); (c) G. Klopman, J. Amer. Chem. Soc., 90, 223 (1968);
(d) L. Salem, ibid., 90, 543 (1968); (e) L. Salem, ibid., 90, 553 (1968); HOMO-LUMO interaction scheme can in a unified
(f) L. Salem, Chem. Brit., 449 (1969) ; (g) A. Devaguet and L. Salem, manner be applied to various processes which have been
J . Amer. Chem. Soc., 91, 3793 (1969).
(5) R. B. Woodward and R. Hoffmann, Angew. Chem., 81, 797 mentioned and discussed by Woodward and Hoff-
(1969); Angew. Chem., Int. Ed. EngZ., 8, 781 (1969); “The Con- m a n r ~ and also to present, at the same time, an ex-
,~
servation of Orbital Symmetry,” Academic Press, New York, N. y.,
1969; and their preceding papers cited therein. tremely simple and practical method to interpret or
(6) R. G. Pearson, Theor. Chim. Acta, 16, 107 (1970). predict the favorable steric pathway. While this
(7) (a) K . Fukui and H. Fujimoto, BUZZ.Chem. SOC. Jap., 41, 1989
(1968) ; (b) K. Fukui and H. Fujimoto, ibid., 42, 3399 (1969). method is general in character, it is particularly suitable
2. 58 KENICHI
FUKUI VOl. 4
for the interpretation of rather complicated reactions
such as intramolecular rearrangements, to which the
correlation diagram method is not always directly
applicable. The theoretical basis is evident in light of
previous paper^.^^^^^ This method is a practical repre-
sentation of the fundamental proposition3,*‘ that a
,7b
majoyity of chemical reactions should take place at the
position and in the direction of maximum overlapping of
the HOMO (or high-lying occupied MO’s) and the LUMO
(or low-lying unoccupied MO’s) of the reacting species; in
reacting species possessing a singly occupied (SO) fVl0, I
this plays the part of the HOMO or of the LUMO, or of
both. Butadiene
Procedure
The process is illustrated in Figure 1 for the simple
case of the thermal ring opening of cyclobutene. Cyclobuteqe
Usually chemical reactions occur in a certain limited
region of the m o l e c ~ l e . ~The ~ ~
~ * region essential to the Figure 1. The mode of the HOAIO-LUX0 iiiteractioii in the
ring-opening of cyclobutene.
conversion in this case is composed of one 7~ bond and
one u bond to be broken and two ir bonds to be formed.
ils a first approximation, it may be sufficient to take
only these bonds into account. The reaction may be change are not always equivalent if the molecule has
initiated by the mutual charge-transfer interaction appropriate substituents. Similar circumstances apply
between the T bond and the u bond to be broken. The to the relation of I1 and 11* of Figure 2. However, a
mode is illustrated in Figure 1. This interaction will useful convention may be adopted here in which we only
take place between the HOR’IO and the LURlO of each refer to the “positive” overlapping such as I or I1 and do
bonding region. The HOMO is bonding and the not care about the “negative” overlapping such as I *
LUMO is antibonding. The charge transfer to the or 11* for the purpose of using the maxinium overlap-
antibonding Lull10 from the bonding HOMO will cause ping criteria. By this convention. the difference in the
the weakening, and accordingly the stretching, of both way of shading, as that between I and 11, which is
bonds. This principle is most easily understood if the physically meaningless, turns out to distinguish two
diatomic case is thought of. An increase in bond length diflerent modes of conversion. The two M ays of shading
will cause a lowering of the LUhIO level and an eleva- the LUIIO part in the models I and I1 are thus regarded
tion of the HOMO energy, so that the charge transfer is as independent alternatives. I n this way, we are able
further facilitated. Such interactions may be assisted to consider hereafter only the direction which leads to
by vibrational motion. As the reaction proceeds, the shaded-shaded and unshaded-unshaded overlappings
donor character of the C=C T bond and the acceptor as the proper one which corresponds to bonding interac-
character of the C-C u bond become distinct, and the tion, and at the same time we have to take all different
contribution of interaction I of Figure 1 becomes more ways of shading which may have the possibility of pro-
important than that of 1’. ducing a nonequivalent direction. Consideration of
The nodal properties of these MO’s are characterized Figure 4d and 4f will be helpful in understanding this
by the schematic diagram (Figure 1). The shaded and relation.
unshaded regions correspond to the plus and minus lobes I n addition to this, a general remark is necessary
of the AlO’s. Figure 1 indicates that the direction of concerning the choice of the region in the molecule in
effective overlapping of HOMO and LUNO in this case which we have to consider the HOMO-1,URIO interac-
is that which is shown by arrows. It is concluded that tion. A fundamental guide may be: the bodering
the conrotatory change5 would be favorable. surface of the two parts between which the HOIIIO-LUMO
Here, a very elementary but important remark might interaction i s considered should be crossed by the newly
be necessary. Each molecular orbital may have an formed bonds (lemma A). This is required since the
indefiniteness by a factor of absolute value unity. Two multicenter interaction between these two parts, taking
different ways of shading are possible for each MO, if we place through the bonds to be formed, is the very
are interested in real functions only. Physically, these origin of the stereoselectivity.
ways represent an identical hI0. Since the interaction The practical value of such a convention will be
energy between two systems, A and B, includes orbital clearer if we use a stereomodel like that shown in Figure
overlapping between RIO’s belonging to , and B in the
4 3. The HOMO and LUMO parts are specified with
form of their absolute value or s q ~ a r e , the mode of
~~~~’ colored pegs, Two different colors are understood to
change I * in Figure 2 can be expected with the same represent the shaded and unshaded lobes of atomic
probability as that of I provided other conditions are the orbitals (AO), For the sake of convenience, the u bond
same. Kote that these two modes of conrotatory to be broken has pegs just like those of sp2carbons and a
3. February 1971 PATHS INTERACTION
STEREOCHEMICAL BY ORBITAL 59
-
c=p
colored pegs
J , dIscannectaale IUlcClOn
w norma1 pegs
Figure 3. A stereomodel for the explanation by orbital inter-
action scheme.
Figure 1 lead to the same conclusion. Therefore only
the more important one of them is indicated in Figure 4 .
I n excited-state reactions, too, only the SOMO-LUR40
interaction is illustrated, since the SO’MO-HOMO
interaction leads to the same conclusion. Symbols for
” Posit i v e” overlapping “ N e g a t i v e ” overlapping the MO’s used are defined in Figure 5 . At the present
Figure 2. A convention used in shading MO’s. stage of development we are forced to proceed with the
assumption of reaction via the lowest excited state for
disconnectable junction, J. The sp3 “tail” pegs allow these photoinduced processes. Literature references
the model to represent the growth of the sp3hybrid to a are completely omitted since the exemplification follows
that of the Woodward-Hoff mann papers6
p A 0 as the reaction proceeds. At first the colored pegs
are properly placed so as to represent the nodal proper- Also, a few well-known examples of intermolecular
ties of the HOMO and LUMO. Then, junction J is processes are indicated in Figure 6 for c o m p a r i ~ o n . ~ * ~
removed and carbons 1 and 4 are rotated to form the 1,2 I n addition, this method applies to stereoselective
acyclic eliminations and addition^.^ The steric prefer-
and 3,4 T bonds in such a way that two pegs of the same
color become parallel on each side of a T bond that is ences of a,p-trans additions and eliminations, cis-a,y-
forming. Of course, as mentioned before, the two non- SN~‘ reactions, a,&cis additions, and photoinduced
equivalent ways of coloring lead to two nonequivalent a,p-cis additions are successfully explained.
pathways in the case of substituted cyclobutenes. We I n several examples of Figure 4, knowledge of a u
LUMO is needed. For such a purpose, the use of
can simultaneously discuss the favorable or unfavorable
steric circumstances with respect to these two paths by hybrid-based MO’s9 is recommended as most con-
the use of such a stereomodel. It is known that the venient. The nodal properties of u MO’s of conjugated
color relation of AO’s between the two newly formed T molecules can be determined through such c a l c ~ l a t i o n s . ~ ~
bonds in the resultant molecule in Figure 311 is not Figures 4 and 6 exemplify two-center interactions,
physically significant since the color of the pegs only and Figure 7 gives examples of three-center reactions.
illustrates the direction of favorable change with These reactions, on the basis of the assumption of con-
respect to the partition of the molecule into the two certedness, can be treated as a combination of two two-
parts illustrated in Figure 11. center interactions in order to predict the direction of
conversion in each bond fission or bond formation.
Examples Note that in each two-center interaction lemma A is
This simple method is powerful from the practical obeyed.
standpoint since it can reproduce the stereoselective Such a stepwise recognition of “concerted” reactions
reaction paths discussed in the comprehensive paper of may at first sight seem to be self-contradictory, but it
Woodward and Hoff man^^ Several examples of intra- may rather be more reasonable than an attempt to
molecular processes are given in Figure 4 (example o is understand every concerted multi-center reaction as a
discussed in ref 8) in which the sketch of a molecular strictly “synchronous” change. Sometimes a bond
model is replaced by the simpler representation as in fission may initiate the whole process, or it may happen
Figure 1 for reasons of simplicity. If the reader experi- that the conversion may start with a bond-forming
ments with a stereomodel, he will find it to be so simple
(9) (a) K. Fukui, “Modern Quantum Chemistry. Istanbul Lec-
and automatic that no explanation of the figure will be tures,” Part I, 0. Sinanoglu, Ed., Academic Press, New York, N. Y.,
needed. In all of the examples mentioned, the two 1965, p 49, and references cited therein; (b) K. Fukui, “Sigma Mo-
lecular Orbital Theory,” 0 . Sinanozlu and K. B. Wiberg, Ed., The
modes of HOMO-LUMO interactions like I and I’ in Yale University Press, New Haven, Conn., 1969, p 121, and refer-
ences cited therein; (0) s. Katagiri and C. Sandorfy, Theor. Chim.
Acta, 4, 203 (1966); (d) J. A. Pople and D. P. Santry, Mol. Phys.,
(8) (a) M. Jones, Jr., and L. T . Scott, J . Amer. Chem. SOC.,
89, 7,269; 8, 1 (1964); (e) K . Fukui, H. Kato, T. Yonesawa, K. Moro-
150 (1967). (b) The S O M O in Figure 40 is the same as the LUMO kuma, A. Imamura, and C. Nagata, Bull. Chem. SOC.Jap., 35, 38
of the ground-state butadiene. (1962).
4. 60 KENICHI
FUKUI Vol. 4
LU
I
-0
( a ) Ring-closure of hexatriene (G).
(c) Bicyclooctadiene isomerization ( E ) .
F’
( b ) Selective rearrangement o f 1,l-dihalocyclopropanes
(G! .
( y ) Cyclization of cyclooctatriene (E).
H3C CHI __L H
H3c% H3
LU H
(c! Bicyclobutane rearrangement ( G ) .
( h ) Cyclization of norbornadiene ( E ) .
X X - yx
&
Y
(1) Cyclization of bicyclooctatrlene ( I : ) .
X
cd) Bicyclization of hexatriene ( E ) .
(1) 1,7-Hydrogen migration (E)
LU
H3
0 1 - 0
(e) Cyclization of cyclohexenone ( E ) (k) Bicycloheptene rearrangement LG)
5. February 1971 STEREOCHEMICAL BY ORBITAL
PATHS INTERACTION 61
(n) Fragmentation o f five-membered diazene ring ( G ) .
(1) Ring-opening of cyclopropyl cation ( G ) .
(c) Isomerization of bicyclo[4.2.2l-deca-2,4,7,9-tetraene
(m) Alkyl migration in bicyclchexenyl cation ( G ) . t o bullvalene (E)
Figure 4. Examples of orbital interaction involved in intramolecular stereospecific processes: (G) ground-state or thermal reaction;
(E) excited-state or photoinduced reaction
Symbol of MO
LU
HO -8--8-
-e--%-
-
* SO'
-8--8-
N LU
so
NHO (a) Diels-Alder addition ( G ) .
ground s t a t e excited state
Figure 5. Symbols used to represent particular molecular orbi-
tals: quot; 0 , next highest occupied; NLU, next lowest unoccu-
pied; SO, SO', singly occupied, high lying and low lying.
(b) Dimerization of olefins (E).
interaction. We can connect the result of theoretical
investigation directly with the mechanism of reaction
and recognize that the driving force in the majority of
reactions may be charge-transfer interaction between a
certain electron-donating part and a certain electron-
accepting part which are temporarily enhanced by
molecular deformation through the elevation of the
HOAIO level and the depression of the LUMO levels of (c) l,?-Dipolar addition ( G )
these parts. The particular circumstances of a given
case can only be understood by looking into actual
examples.
Extension
(a) Subsidiary Effects. As mentioned before, the
HOMO-LUMO interaction scheme has been employed
for interpretation of the exo-endo selectivity in Diels-
Alder-type cycloaddition^.^^^^
A rather sophisticated way of understanding the (d) Dimerization of cyclobutadiene (G).
boat-chair selectivity in the Cope rearrangement, which Figure 6. Examples of intermolecular processes.
was adopted in the explanation given by Woodward
and Hoffmann,6 can be replaced by one based on the SOMO interaction has nothing to do with this selec-
orbital interaction scheme. The nonbonding SOMO- tivity since these MO's have a node at the central car-
6. 62 KENICHI
FUKUI Vol. 4
(a) Cope rearrangement fc) .
!b) Addition of olefin to norharcadiene !G)
Chair Boat
Figure 8. The boat-chair selectivity in the Cope rearrangement.
(c) 1,4-kllyA ~ i g r a t i a n (2).
is 1,3-dimethylcyclopropene,and 4-methylcyclobutene
is not found. Diagrams ii-1 and ii-2 show that these
Figure 7 . Examples of three-center reactions. processes do not meet the requirement of lemma B.
It is intersting to look into the reason why the
bon, as indicated in Figure 8. Consideration of NHO- biradical
and KLU-AI0 interactions leads to understanding the
preference for chair-form transition states.
(b) Multiplicity Selectivity. The behavior of excited
intermediates in the triplet state may be specified by
their tendency to adopt a configuration in which two
unpaired electrons are as far away as possible from each is not formed in the process of i and ii-3. I n this con-
other, as is expected theoretically. For instance, nection one should take into account the fact that the
cyclization in an excited triplet state can be specified by LUMO of propylene has a large extension a t the carbon
stating that cyclization usually takes place so as to pass atom attached to methyl. An exaggerated sketch for
through an intermediate which does not contain two
unpaired electrons in one ring or in one conjugated
chain, while an excited singlet-state reaction has no such LUMO H3C-CCC HOMO H?C-C=C
restriction.l0 I n this connection, the following lemma
can be combined with the preceding method to predict
the difference between triplet and singlet reactivi-
ties.11-13 It is to be noted that concertedness is not the mode of interaction may be
necessarily expected in these cases. I n a triplet-state
reaction each bond, which i s to be newly formed through the
overlapping of AO’s of the two parts where the orbital
interaction i s comiderecl, should be formed so a s to result in
a structure having two unpaired electrons not in conjuga-
tion with each other by virtue of that bond (lemma B).
Excited singlet-state reactions are not necessarily
subject to such a limitation.
Figure 9 illustrates these circumstances. Figure 9A
concerns the excited-state reaction of l13-pentadi-
Figure 9B deals with the difference in reactivity in
ene.11v12 I n the triplet-state reaction, the main product 0,yunsaturated ketones. All example^'^^'^ are con-
sidered to take place through the transfer of a n,x*
(10) S. Kita and K. Rukui, Bull. Chem. Soc. Jap.,42, 66 (1969). triplet to a T,T* triplet. The examples of Figure 4e
(11) (a) R. Srinivasan and S.BouB, Tetrahedron Lett., 203 (1970);
(b) R . Srinivasan, J . Amer. Chem. Soc., 84, 4141 (1962). seem t o belong to triplet-state reactions of the same
(12) S. Bou6 and R. Srinivasan, ibid., 92, 3226 (1970). categ0ry.j It has been established that the reaction of
(13) (a) E. Baggiolini, K. Schaffner, and 0 . Jeger, Chem. Commicn.,
1103 (1969) ; (b) J. Ipaktschi, Tetrahedron Lett., 215 (1969) ; ( c ) W.
G. Dauben, M. S. Kellogg, J. I. Seeman, and W.A. Spiteer, J.Amer. (14) I am grateful to Dr. A . Kende for supplying me with experi-
Chem. Soc., 92, 1786 (1970). mental facts.
7. February 1971 STEREOCHEMICAL BY ORBITAL
PATHS INTERACTION 63
(i) Triplet-state r e a c t i o n L L a
(ii) singlet-state reaction
so 4 LU
SO‘ * -8---8- HO
-#--e-
hu
----e
a) Formation o f benzvalene from benzene16
s n n
ii-3lLC ( s a m e figure a s (i)) hu
(A) Photoinduced reaction of 1,a-pentadiene LU
Ii) Singlet reaction
0
R
hu
b) Formation of semibullvalene from c y c l ~ o c t a t e t r a e n e , ~ ’
R Figure 10. Examples of photoinduced multicyclization.
ucts in complicated photochemical multicyclization
I l l ) Triplet reaction processes of unsaturated systems. Although it may
0
not be possible to establish concertedness, this is never
an essential ;point in the present discussion. Examples
of some multicyclization processes are illustrated in
R
-F0
h’ R‘
Figure 10.
Merits
0 The HOMO-LUMO interaction scheme, in combina-
R’
tion with a numerical calculation, is obviously appli-
cable to any system with ambiguous symmetry proper-
ties. It may happen that the conjugative influence of
Examples o f B,y-unsaturated ketones:
neighboring parts exerts an influence on the orbital ex-
tension and on the nodal properties of the HOMO or
LUMO, and, clearly, this method applies even in such
cases and can give information on these eff ects.
(ref. 13a) (ref. 13b) (ref. 13c) Orbital symmetry is a most important factor in deter-
(B)Photoinduced reaction of 0,y-unsaturated ketones
mining the magnitude of delocalization stabilization due
to the HOMO-LUMO o ~ e r l a p p i n g . ~ ~ ~
However, it
Figure 9. T h e singlet-triplet selectivity.
Figure 4i proceeds through a triplet state.’s All of (15) H. E. Zimmerman, R . W. Binkley, R. S. Givens, G. L.
Grunewald, and M. A. Sherwin, J. Amer. Chem. Soc., 91, 3316
these cases satisfy the requirement of lemma B. (1969).
(c) Multicyclization. A useful extension of these (16) K. E.Wilsbaoh, J. S. Ritscher, and L. Kaplan, ibid., 89, 1031
(1967).
ideas might be the prediction of the structure of prod- (17) H.E.Zimmerman and H. Iwamura, $bid., 90,4763 (1968).
8. 64 KENICHI
FUKUI VOl. 4
pointed out that the orbital interaction scheme can
always give the directional features of the reaction
mechanism at the point of initiation and the force which
acts along the reaction path and thus drives the system
to further conversion. In this connection, the use of
stereomodels mill facilitate the discarding of difficultly
accessible steric paths when it is combined with con-
sideration of positive overlap of the particular orbitals
previously mentioned.
An interesting application of this method is the
explanation of the catalytic action of d-orbital participa-
tion which causes an otherwise “symmetry-forbidden”
(a! Cycloprapyl r a d i c a l reaction to become Applications are also
possible to the prediction of molecular stability and the
stability of configurations of molecular species3dand to
explanations of Lfspiroconjugation”*o and “bicyclo-
W$< aromaticity, ”21
LU -2 LU
This method requires no selection rule and is com-
.-
4
pletely automatic. Usually, only knowledge of the
HOnIO and LUMO of very simple systems is needed,
and this makes the theory quite simple and extendable
and gives it a uniform character.
Of course, reactivity in all types of unicentric reac-
tions of saturated and unsaturated compounds can be
(b, Cycloprapanone
interpreted by the HOMO-LURIO interaction
method.*v3 Problems of orientation and stereoselection
Figure 11. Continuity in the stereoselection in thermal ring- can thus be discussed in a unified fashion by this ap-
opening reactions.
proach.
should be noted that the existence of symmetry elements So far, few contradictions have been found between
in orbitals is not essential in the recognition of favorable predictions based on the correlation diagram method
reaction paths. This point should be obvious from the and the orbital interaction criteria, but the latter are
previous discussion. able to treat many problems which are beyond the reach
The examples shown in Figure 11 illustrate that of the former method.
stereospecificity is predicted to be continuous, provided The understanding of coniplicated stereospecific
that the related factors are continuous. In the ring- organic reactions and the generalization of stereoselec-
opening reactions of cyclopropyl radical (a), the results tion rules made by Woodward and Hoffmann are
of prediction by a LUMO-SOMO interaction (i) and unquestionably valuable. A relevant x a y of reasoning
HO?(IIO-SOMO interaction (ii) are opposite. The to a result should lead to an understanding of the under-
favorable path may be subject to substituent effects as lying nature of chemical reactions. The correlation
well as electrocyclic control. Elevation of the SOAIO diagram method based on the principle of conservation
energy will make the LUMO-SOMO interaction domi- of orbital symmetry is one way of reasoning; however,
nant, and lowering of the S O N O level may increase the the orbital interaction scheme appears to be more unifi-
importance of HOMO-SOMO interaction. I n this cative and wider in scope, and it gives more direct
way, the direction of change may vary.18 A similar descriptions of the nature of chemical reactions.
situation is expected in the ring opening of cyclo-
propanone (b). However, in view of the large ampli- T h i s work was done during m y stay at Illinois Institute of Tech-
tude of the LUblO at the carbonyl carbon in this nology as a National Science Foundation Senior Foreign Scientist
Fellow. I am also pleased to thank Dr. S. I . Miller of Illinois
instance, case i is expected to p r e ~ a i 1 . l ~ Institute of Technology and Dr. H . Fujimoto of Kyoto University
As one of the merits of the present method, it may be for helpful comments.
(18) Cf. H. C. Longuet-Higgins and E. W. Abrahamson, J.
Amer. Chem. SOC..87.2045 119661. (201 H. E. Simmons and T. Fukunaaa. J. Amer. Chem. Soc.. 89,
-
(19) Cf.the prediction m&deby N. J. Turro, Accounts Chem. Res., 5208 (1967).
2, 26 (1969). (21) M. J. Goldstein, ibid., 89, 6367 (1967).