1. Conjugated systems with multiple double bonds have increased stability due to delocalization of pi electrons over the entire system. This stabilization increases reactivity for electrophilic additions.
2. Allylic positions adjacent to double bonds have increased reactivity due to stabilization of allylic radicals, cations and transition states by resonance with the pi system. This leads to faster halogenation, SN1 and SN2 reactions at allylic sites.
3. Extended conjugation over multiple double bonds confers increased thermodynamic stability but also increased reactivity towards electrophilic additions and radical reactions compared to shorter conjugated systems.
This document discusses various types of organic reactions including ionic reactions, radical reactions, and nucleophilic substitution reactions. It provides details on:
1) The mechanisms of SN1 and SN2 reactions including rate laws, stereochemistry, substrate structure effects, and effects of nucleophiles, leaving groups, and solvents. SN1 reactions proceed through a carbocation intermediate and follow first-order kinetics while SN2 reactions are bimolecular.
2) Substrate structures that favor SN1 or SN2 reactions. Tertiary substrates favor SN1 while primary and secondary favor SN2. Allylic and benzylic compounds are more reactive in both SN1 and SN2 reactions.
3)
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.
Nitrenes slideshare Reactive intermediatesDivyarani K
The document discusses nitrenes, which are electron deficient nitrogen species that can exist in singlet or triplet states. It describes various methods for generating nitrenes, such as through the decomposition of azides or oxidation of primary amino groups. The document also outlines several reactions of nitrenes, including their ability to insert into carbon-hydrogen bonds or undergo rearrangement reactions like the Hofmann, Curtius, Lossen, and Schmidt rearrangements.
Nucleophilic substitution reactions involve a nucleophile reacting with an alkyl halide substrate by replacing the halogen leaving group. There are two types of nucleophilic substitution reactions: SN1 and SN2. In an SN1 reaction, the alkyl halide first undergoes heterolysis to form a carbocation intermediate which the nucleophile then attacks. The rate depends only on the concentration of the alkyl halide. In contrast, an SN2 reaction is a concerted bimolecular process where the nucleophile attacks the alkyl halide as the C-X bond breaks. The rate depends on both the concentrations of the alkyl halide and nucleophile.
1) Benzylic radicals are reactive intermediates in the α-halogenation of alkylbenzenes. Benzylic halogenation proceeds without use of a catalyst like FeBr3 and involves benzylic cation and SN2 reaction mechanisms.
2) Phenol synthesis can occur through three mechanisms - nucleophilic aromatic substitution when electron-withdrawing groups are present, elimination-addition via highly reactive benzyne intermediates under harsh conditions, or using arenediazonium salts with super-leaving nitrogen groups.
3) Phenols are weakly acidic due to resonance stabilization of the phenoxide anion. They undergo electrophilic aromatic substitution and other reactions like ether and ester formation. O
Kajal Patel presented on nucleophilic displacement reactions to the M.Sc class. The presentation covered SN1 and SN2 reactions.
SN1 reactions are nucleophilic substitutions that proceed through a carbocation intermediate. They are unimolecular, depending only on the concentration of one reactant, and lose stereochemistry. SN2 reactions are also nucleophilic substitutions, but are bimolecular and proceed in one step via a backside attack, resulting in inversion of configuration.
This document discusses various types of organic reactions including ionic reactions, radical reactions, and nucleophilic substitution reactions. It provides details on:
1) The mechanisms of SN1 and SN2 reactions including rate laws, stereochemistry, substrate structure effects, and effects of nucleophiles, leaving groups, and solvents. SN1 reactions proceed through a carbocation intermediate and follow first-order kinetics while SN2 reactions are bimolecular.
2) Substrate structures that favor SN1 or SN2 reactions. Tertiary substrates favor SN1 while primary and secondary favor SN2. Allylic and benzylic compounds are more reactive in both SN1 and SN2 reactions.
3)
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.
Nitrenes slideshare Reactive intermediatesDivyarani K
The document discusses nitrenes, which are electron deficient nitrogen species that can exist in singlet or triplet states. It describes various methods for generating nitrenes, such as through the decomposition of azides or oxidation of primary amino groups. The document also outlines several reactions of nitrenes, including their ability to insert into carbon-hydrogen bonds or undergo rearrangement reactions like the Hofmann, Curtius, Lossen, and Schmidt rearrangements.
Nucleophilic substitution reactions involve a nucleophile reacting with an alkyl halide substrate by replacing the halogen leaving group. There are two types of nucleophilic substitution reactions: SN1 and SN2. In an SN1 reaction, the alkyl halide first undergoes heterolysis to form a carbocation intermediate which the nucleophile then attacks. The rate depends only on the concentration of the alkyl halide. In contrast, an SN2 reaction is a concerted bimolecular process where the nucleophile attacks the alkyl halide as the C-X bond breaks. The rate depends on both the concentrations of the alkyl halide and nucleophile.
1) Benzylic radicals are reactive intermediates in the α-halogenation of alkylbenzenes. Benzylic halogenation proceeds without use of a catalyst like FeBr3 and involves benzylic cation and SN2 reaction mechanisms.
2) Phenol synthesis can occur through three mechanisms - nucleophilic aromatic substitution when electron-withdrawing groups are present, elimination-addition via highly reactive benzyne intermediates under harsh conditions, or using arenediazonium salts with super-leaving nitrogen groups.
3) Phenols are weakly acidic due to resonance stabilization of the phenoxide anion. They undergo electrophilic aromatic substitution and other reactions like ether and ester formation. O
Kajal Patel presented on nucleophilic displacement reactions to the M.Sc class. The presentation covered SN1 and SN2 reactions.
SN1 reactions are nucleophilic substitutions that proceed through a carbocation intermediate. They are unimolecular, depending only on the concentration of one reactant, and lose stereochemistry. SN2 reactions are also nucleophilic substitutions, but are bimolecular and proceed in one step via a backside attack, resulting in inversion of configuration.
The document summarizes key aspects of SN2 reactions including reaction mechanism, kinetics, stereochemistry, and factors that affect the rate of the reaction. It describes the SN2 reaction as a bimolecular nucleophilic substitution where the nucleophile attacks the substrate simultaneously as the leaving group departs, resulting in an inversion of configuration. Rate depends on both the nucleophile and substrate concentrations. The stability of the transition state is affected by substrate structure, nucleophilicity, leaving group ability, solvent properties, and conjugation effects in allylic and benzylic systems. Cyclic substrates and those without available orbital overlap do not undergo SN2 reactions as easily.
Aldehydes and ketones contain a carbonyl group consisting of a carbon double-bonded to an oxygen. Chapter 17 discusses the properties, nomenclature, synthesis, and reactions of aldehydes and ketones. Key reactions include nucleophilic additions to the carbonyl carbon to form alcohols, such as hydration to form geminal diols or addition of alcohols or amines. Other reactions include oxidations of alcohols to form aldehydes or ketones, and reductions of aldehydes or ketones using reagents such as sodium borohydride or lithium aluminum hydride.
Nucleophilic aromatic substitution reactions follow an addition-elimination mechanism known as SNAr. The rate-determining step is the formation of a cyclohexadienyl anion intermediate through nucleophilic attack. Electron-withdrawing groups stabilize this intermediate through resonance, making the reaction faster. Nucleophilic aromatic substitution is most favorable when the leaving group is fluoride and least with iodide, and occurs readily with strong nucleophiles like hydroxide or cyanide in the presence of electron-withdrawing groups ortho or para to the reaction site.
This document provides a summary of nucleophilic substitution reactions. It discusses the mechanisms of SN1 and SN2 reactions. SN1 is a two-step, unimolecular reaction that proceeds through a carbocation intermediate. It favors tertiary halogenoalkanes due to stability of the carbocation. SN2 is a one-step, bimolecular reaction where bond breaking and formation occur simultaneously. It favors primary halogenoalkanes due to less steric hindrance allowing frontside attack. Factors like the nature of the halogen, halogenoalkane, and nucleophile affect the rate of these substitution reactions.
Nucleophilic substitution reactions can occur through either an SN1 or SN2 mechanism. The SN1 reaction is a two-step process where the first step is rate-determining and involves formation of a carbocation intermediate. It is a unimolecular reaction that results in loss of configuration. The SN2 reaction is a single concerted step where nucleophilic attack and leaving of the existing group occur simultaneously through a trigonal planar transition state. It results in inversion of configuration. Both mechanisms are affected by factors like the substrate structure, the nucleophile, the leaving group and the solvent used.
Carbenes- octet defying molecules, its fate, reactions, synthesis of carbenoids,spin multiplicity of carbenes triplet, singlet carbenes, Fischer and Schrock carbenes
1) Elimination reactions occur when two atoms or groups are removed from two adjacent carbon atoms of a substrate molecule to form a multiple bond.
2) Elimination occurs when a nucleophile attacks a hydrogen instead of a carbon.
3) In an E1 elimination reaction, the leaving group leaves in the rate-determining unimolecular step, and the proton is removed in a separate second step.
The Diels-Alder reaction is a [4+2] cycloaddition between a conjugated diene and a substituted alkene (dienophile) to form a cyclohexene ring. It was discovered in 1928 by Otto Diels and Kurt Alder. The reaction proceeds in a single, concerted step through a transition state and can be accelerated by heating or using catalysts. It is useful for synthesizing 6-membered rings in a stereoselective and stereospecific manner. Lewis acids are commonly used to catalyze the reaction by activating the dienophile. Chiral dienes and dienophiles, as well as chiral Lewis acids, allow for asymmetric Diels-A
Nucleophilic substitution sn1 sn2 nucleophile halogenoalkane in organic chemi...DocumentStory
This document discusses nucleophilic substitution reactions, specifically SN1 and SN2 mechanisms. SN1 is a two-step reaction that proceeds through a carbocation intermediate, depending on the concentration of the substrate. SN2 is a one-step bimolecular reaction where bond breaking and formation occur simultaneously. Tertiary halogenoalkanes typically undergo SN1, while primary halogenoalkanes usually undergo SN2 due to steric and inductive effects. Factors like the nature of the halogen, halogenoalkane, and nucleophile affect the rate of these substitution reactions.
The document discusses how changing the covalent radius of bonds in organic compounds can alter their properties. It presents that increasing the covalent radius will increase the distance between bonded atoms. This increased distance leads to lower melting points, boiling points, and tensile strength. The document constructs virtual models of organic compounds to demonstrate how compounds with the same structure but different covalent radii will have varying distances between atoms and altered properties as a result. It concludes that producing new properties in organic compounds can be achieved by modifying the covalent bond radius.
This document provides an overview of various carbon-based reaction intermediates including carbocations, carbanions, carbenes, free radicals, nitrenes, and nitrenium ions. It discusses their generation, structure, stability, reactions, and detection methods. Key points include that carbocations are positively charged carbon species that react as electrophiles, while carbanions are negatively charged carbon species that react as nucleophiles. Carbenes contain a carbon with six valence electrons in a triplet or singlet state. Free radicals contain one or more unpaired electrons. Nitrenes and nitrenium ions involve a reactive nitrogen species. Detection methods include NMR, EPR, UV-Vis spectroscopy, and trapping reactions.
1) The document summarizes different reaction mechanisms for nucleophilic substitution including SNi, SN1', SN2', SN1cA, and SN2cA.
2) SNi involves nucleophilic substitution with retention of configuration where part of the leaving group attacks.
3) SN1' occurs with allylic substrates under SN1 conditions producing normal and rearranged products due to resonance of the allylic carbocation.
4) SN2' is an allylic rearrangement that can occur under SN2 conditions where the nucleophile attacks the γ-carbon.
5) SN1cA and SN2cA involve a preliminary protonation step to convert a non-leaving
1. The document summarizes SN1 and SN2 reactions of alkyl halides. SN1 reactions proceed through a carbocation intermediate and are 1st order, while SN2 reactions involve direct attack of the nucleophile and are 2nd order.
2. The rate of SN2 reactions depends on factors like the substrate structure, nucleophile strength, leaving group ability, and solvent. Methyl substrates react fastest while tertiary substrates are inert. Polar aprotic solvents increase the rate.
3. SN1 reactions are favored for tertiary substrates. The mechanism involves heterolytic cleavage to form a carbocation, then nucleophilic attack. Stable carbocations like allylic and benzylic ones react
Organic compounds containing an electronegative atom or electron-withdrawing group bonded to a carbon undergo substitution or elimination reactions. Alkyl halides specifically undergo SN1, SN2, E1, and E2 reactions. SN1 and E1 are unimolecular reactions that proceed through a carbocation intermediate, while SN2 and E2 are bimolecular reactions. The type of reaction depends on factors like the nucleophile strength and leaving group ability.
This document discusses electrophilic aromatic substitution on benzene derivatives. It explains that substituents can either activate or deactivate the benzene ring towards electrophilic attack by induction or resonance effects. Donor groups activate by directing electrophiles to the ortho- and para-positions, while acceptor groups deactivate by directing to the meta-position. Oxidation can convert an activator into a deactivator or vice versa. Strategies like protection/deprotection, reversible blocking, and multi-step synthesis are used to overcome reactivity issues. Electrophilic substitution in polycyclic aromatic compounds is also discussed.
1. The document discusses mechanisms of substitution and elimination reactions for alkyl halides, including SN1, SN2, E1 and E2.
2. Key factors that determine the reaction mechanism are the structure of the alkyl halide (primary, secondary, tertiary), the nucleophilicity and basicity of the reaction conditions, and temperature.
3. SN1 proceeds through a carbocation intermediate and gives racemic products. SN2 is stereospecific. E1 and E2 are elimination reactions favored by strong bases and high temperatures.
1. The document discusses mechanisms of substitution and elimination reactions for alkyl halides, including SN1, SN2, E1 and E2.
2. Key factors that determine the reaction mechanism are the structure of the alkyl halide (primary, secondary, tertiary), the nucleophilicity and basicity of the reaction conditions, and temperature.
3. SN1 proceeds through a carbocation intermediate and gives racemic products. SN2 is stereospecific. E1 and E2 are elimination reactions that compete with substitution.
This document discusses the sources and properties of alkanes and cycloalkanes. It notes that crude oil and refinery gas are the main sources, and refining processes like cracking and reforming are used to produce more useful products. The boiling points of alkanes are determined by induced dipole-induced dipole interactions, which increase with carbon chain length and decrease with branching. Alkanes combust completely to produce carbon dioxide and water, with heat of combustion increasing with chain length but decreasing for branched alkanes. Oxidation of carbon corresponds to increasing its bond to more electronegative oxygen or decreasing bonds to hydrogen.
1) Benzylic radicals are reactive intermediates in the α-halogenation of alkylbenzenes. Benzylic halogenation proceeds without use of a catalyst like FeBr3 and involves benzylic cation and SN2 reaction mechanisms.
2) Phenol synthesis can occur through three mechanisms - nucleophilic aromatic substitution when electron-withdrawing groups are present, elimination-addition via highly reactive benzyne intermediates under harsh conditions, or using arenediazonium salts with a super-leaving nitrogen group.
3) Phenols are weakly acidic due to resonance stabilization of the phenoxide anion. They undergo electrophilic aromatic substitution and other reactions like ether and ester formation.
Basic principles & questions and answers of organic chemistry Bryar Ali Rus
this is some basic principles and question & answers of previous years of organic chemistry with notes on dr.emad manhal's examination , school of pharmacy , university of sulaimani .
The document summarizes key aspects of SN2 reactions including reaction mechanism, kinetics, stereochemistry, and factors that affect the rate of the reaction. It describes the SN2 reaction as a bimolecular nucleophilic substitution where the nucleophile attacks the substrate simultaneously as the leaving group departs, resulting in an inversion of configuration. Rate depends on both the nucleophile and substrate concentrations. The stability of the transition state is affected by substrate structure, nucleophilicity, leaving group ability, solvent properties, and conjugation effects in allylic and benzylic systems. Cyclic substrates and those without available orbital overlap do not undergo SN2 reactions as easily.
Aldehydes and ketones contain a carbonyl group consisting of a carbon double-bonded to an oxygen. Chapter 17 discusses the properties, nomenclature, synthesis, and reactions of aldehydes and ketones. Key reactions include nucleophilic additions to the carbonyl carbon to form alcohols, such as hydration to form geminal diols or addition of alcohols or amines. Other reactions include oxidations of alcohols to form aldehydes or ketones, and reductions of aldehydes or ketones using reagents such as sodium borohydride or lithium aluminum hydride.
Nucleophilic aromatic substitution reactions follow an addition-elimination mechanism known as SNAr. The rate-determining step is the formation of a cyclohexadienyl anion intermediate through nucleophilic attack. Electron-withdrawing groups stabilize this intermediate through resonance, making the reaction faster. Nucleophilic aromatic substitution is most favorable when the leaving group is fluoride and least with iodide, and occurs readily with strong nucleophiles like hydroxide or cyanide in the presence of electron-withdrawing groups ortho or para to the reaction site.
This document provides a summary of nucleophilic substitution reactions. It discusses the mechanisms of SN1 and SN2 reactions. SN1 is a two-step, unimolecular reaction that proceeds through a carbocation intermediate. It favors tertiary halogenoalkanes due to stability of the carbocation. SN2 is a one-step, bimolecular reaction where bond breaking and formation occur simultaneously. It favors primary halogenoalkanes due to less steric hindrance allowing frontside attack. Factors like the nature of the halogen, halogenoalkane, and nucleophile affect the rate of these substitution reactions.
Nucleophilic substitution reactions can occur through either an SN1 or SN2 mechanism. The SN1 reaction is a two-step process where the first step is rate-determining and involves formation of a carbocation intermediate. It is a unimolecular reaction that results in loss of configuration. The SN2 reaction is a single concerted step where nucleophilic attack and leaving of the existing group occur simultaneously through a trigonal planar transition state. It results in inversion of configuration. Both mechanisms are affected by factors like the substrate structure, the nucleophile, the leaving group and the solvent used.
Carbenes- octet defying molecules, its fate, reactions, synthesis of carbenoids,spin multiplicity of carbenes triplet, singlet carbenes, Fischer and Schrock carbenes
1) Elimination reactions occur when two atoms or groups are removed from two adjacent carbon atoms of a substrate molecule to form a multiple bond.
2) Elimination occurs when a nucleophile attacks a hydrogen instead of a carbon.
3) In an E1 elimination reaction, the leaving group leaves in the rate-determining unimolecular step, and the proton is removed in a separate second step.
The Diels-Alder reaction is a [4+2] cycloaddition between a conjugated diene and a substituted alkene (dienophile) to form a cyclohexene ring. It was discovered in 1928 by Otto Diels and Kurt Alder. The reaction proceeds in a single, concerted step through a transition state and can be accelerated by heating or using catalysts. It is useful for synthesizing 6-membered rings in a stereoselective and stereospecific manner. Lewis acids are commonly used to catalyze the reaction by activating the dienophile. Chiral dienes and dienophiles, as well as chiral Lewis acids, allow for asymmetric Diels-A
Nucleophilic substitution sn1 sn2 nucleophile halogenoalkane in organic chemi...DocumentStory
This document discusses nucleophilic substitution reactions, specifically SN1 and SN2 mechanisms. SN1 is a two-step reaction that proceeds through a carbocation intermediate, depending on the concentration of the substrate. SN2 is a one-step bimolecular reaction where bond breaking and formation occur simultaneously. Tertiary halogenoalkanes typically undergo SN1, while primary halogenoalkanes usually undergo SN2 due to steric and inductive effects. Factors like the nature of the halogen, halogenoalkane, and nucleophile affect the rate of these substitution reactions.
The document discusses how changing the covalent radius of bonds in organic compounds can alter their properties. It presents that increasing the covalent radius will increase the distance between bonded atoms. This increased distance leads to lower melting points, boiling points, and tensile strength. The document constructs virtual models of organic compounds to demonstrate how compounds with the same structure but different covalent radii will have varying distances between atoms and altered properties as a result. It concludes that producing new properties in organic compounds can be achieved by modifying the covalent bond radius.
This document provides an overview of various carbon-based reaction intermediates including carbocations, carbanions, carbenes, free radicals, nitrenes, and nitrenium ions. It discusses their generation, structure, stability, reactions, and detection methods. Key points include that carbocations are positively charged carbon species that react as electrophiles, while carbanions are negatively charged carbon species that react as nucleophiles. Carbenes contain a carbon with six valence electrons in a triplet or singlet state. Free radicals contain one or more unpaired electrons. Nitrenes and nitrenium ions involve a reactive nitrogen species. Detection methods include NMR, EPR, UV-Vis spectroscopy, and trapping reactions.
1) The document summarizes different reaction mechanisms for nucleophilic substitution including SNi, SN1', SN2', SN1cA, and SN2cA.
2) SNi involves nucleophilic substitution with retention of configuration where part of the leaving group attacks.
3) SN1' occurs with allylic substrates under SN1 conditions producing normal and rearranged products due to resonance of the allylic carbocation.
4) SN2' is an allylic rearrangement that can occur under SN2 conditions where the nucleophile attacks the γ-carbon.
5) SN1cA and SN2cA involve a preliminary protonation step to convert a non-leaving
1. The document summarizes SN1 and SN2 reactions of alkyl halides. SN1 reactions proceed through a carbocation intermediate and are 1st order, while SN2 reactions involve direct attack of the nucleophile and are 2nd order.
2. The rate of SN2 reactions depends on factors like the substrate structure, nucleophile strength, leaving group ability, and solvent. Methyl substrates react fastest while tertiary substrates are inert. Polar aprotic solvents increase the rate.
3. SN1 reactions are favored for tertiary substrates. The mechanism involves heterolytic cleavage to form a carbocation, then nucleophilic attack. Stable carbocations like allylic and benzylic ones react
Organic compounds containing an electronegative atom or electron-withdrawing group bonded to a carbon undergo substitution or elimination reactions. Alkyl halides specifically undergo SN1, SN2, E1, and E2 reactions. SN1 and E1 are unimolecular reactions that proceed through a carbocation intermediate, while SN2 and E2 are bimolecular reactions. The type of reaction depends on factors like the nucleophile strength and leaving group ability.
This document discusses electrophilic aromatic substitution on benzene derivatives. It explains that substituents can either activate or deactivate the benzene ring towards electrophilic attack by induction or resonance effects. Donor groups activate by directing electrophiles to the ortho- and para-positions, while acceptor groups deactivate by directing to the meta-position. Oxidation can convert an activator into a deactivator or vice versa. Strategies like protection/deprotection, reversible blocking, and multi-step synthesis are used to overcome reactivity issues. Electrophilic substitution in polycyclic aromatic compounds is also discussed.
1. The document discusses mechanisms of substitution and elimination reactions for alkyl halides, including SN1, SN2, E1 and E2.
2. Key factors that determine the reaction mechanism are the structure of the alkyl halide (primary, secondary, tertiary), the nucleophilicity and basicity of the reaction conditions, and temperature.
3. SN1 proceeds through a carbocation intermediate and gives racemic products. SN2 is stereospecific. E1 and E2 are elimination reactions favored by strong bases and high temperatures.
1. The document discusses mechanisms of substitution and elimination reactions for alkyl halides, including SN1, SN2, E1 and E2.
2. Key factors that determine the reaction mechanism are the structure of the alkyl halide (primary, secondary, tertiary), the nucleophilicity and basicity of the reaction conditions, and temperature.
3. SN1 proceeds through a carbocation intermediate and gives racemic products. SN2 is stereospecific. E1 and E2 are elimination reactions that compete with substitution.
This document discusses the sources and properties of alkanes and cycloalkanes. It notes that crude oil and refinery gas are the main sources, and refining processes like cracking and reforming are used to produce more useful products. The boiling points of alkanes are determined by induced dipole-induced dipole interactions, which increase with carbon chain length and decrease with branching. Alkanes combust completely to produce carbon dioxide and water, with heat of combustion increasing with chain length but decreasing for branched alkanes. Oxidation of carbon corresponds to increasing its bond to more electronegative oxygen or decreasing bonds to hydrogen.
1) Benzylic radicals are reactive intermediates in the α-halogenation of alkylbenzenes. Benzylic halogenation proceeds without use of a catalyst like FeBr3 and involves benzylic cation and SN2 reaction mechanisms.
2) Phenol synthesis can occur through three mechanisms - nucleophilic aromatic substitution when electron-withdrawing groups are present, elimination-addition via highly reactive benzyne intermediates under harsh conditions, or using arenediazonium salts with a super-leaving nitrogen group.
3) Phenols are weakly acidic due to resonance stabilization of the phenoxide anion. They undergo electrophilic aromatic substitution and other reactions like ether and ester formation.
Basic principles & questions and answers of organic chemistry Bryar Ali Rus
this is some basic principles and question & answers of previous years of organic chemistry with notes on dr.emad manhal's examination , school of pharmacy , university of sulaimani .
Nucleophilic substitution reactions involve a nucleophile (Nu) attacking an electrophilic center (E) bonded to a leaving group (L). The C-X bond is polarized with the electron density pulled towards the more electronegative atom. Nucleophilicity and leaving group ability depend on factors like charge, basicity, size, polarizability, and hydrogen bonding ability. In general, nucleophilicity increases down a group and across a period, while leaving group ability increases down a group and decreases across a period. Steric effects are also important, with bulky substituents disfavoring the approach of nucleophiles to the electrophilic center.
This document discusses energetics topics including standard enthalpies, Born-Haber cycles, and lattice energies. It provides an example of using enthalpies of formation to calculate the standard enthalpy change of a reaction. It also explains the Born-Haber cycle which can be used to calculate lattice energies by comparing the enthalpy of forming an ionic compound to the enthalpies of forming the constituent ions from their elements. Factors that affect lattice energy such as ion size and charge are also discussed.
Aldehydes and ketones contain a carbonyl functional group consisting of a carbon double-bonded to an oxygen. They exhibit characteristic reactivity including nucleophilic addition reactions that form alcohols. Aldehydes and ketones undergo hydration to form geminal diols, addition of alcohols to form hemiacetals and acetals, and addition of amines to form imines through a condensation reaction. Their carbonyl group absorbs strongly in the infrared region and gives deshielded peaks in NMR spectroscopy due to polarization effects.
Photoisomerisation of aromaric compounds [recovered]KANUPRIYASINGH19
The document summarizes various photochemical reactions of aromatic compounds including photoisomerization and photoaddition reactions. It discusses how benzene and substituted benzenes undergo valence isomerization upon irradiation, forming meta and ortho products from excitation to S1 and S2 states respectively. It also describes the 1,2, 1,3 and 1,4 photoaddition reactions of alkenes to aromatic compounds, with the major products and mechanisms discussed for each. Examples of specific reactions like the 1,3 cycloaddition of ethene to benzene forming prefulvene are provided.
1. The document discusses nucleophilic substitution (SN1 and SN2) reactions, where a nucleophile replaces a leaving group on a substrate.
2. It describes factors that determine the rate of these reactions, such as the nucleophilicity of the nucleophile, stability of the leaving group, and structure of the substrate. Tertiary substrates typically undergo SN1 while primary typically undergo SN2.
3. SN1 is a two-step reaction involving a carbocation intermediate, while SN2 is a single-step reaction with inversion of configuration.
The document discusses various types of aliphatic nucleophilic substitution reactions and their mechanisms. It covers SN2 and SN1 mechanisms in detail, providing evidence that supports each. It also discusses borderline cases where reactions have characteristics of both SN1 and SN2, and other mechanisms like SN1', SNi, SET, and addition-elimination that may occur under different conditions. Specific examples of nucleophilic substitution are discussed at allylic, trigonal, and vinylic carbons that may proceed by different pathways than typical SN1 or SN2 reactions.
This document provides an overview of organic chemistry concepts including bonding, molecular structure, and common functional groups. It begins with a brief history of the field and then covers topics such as ionic and covalent bonding, Lewis structures, resonance, and the shapes of molecules determined by valence electron repulsion. Key figures mentioned include Gilbert Lewis, who developed Lewis structures to represent covalent bonding in molecules.
This document provides an overview of organic chemistry concepts including bonding, functional groups, and reactions. It begins with Lewis structures which use octet rules to distribute valence electrons between atoms to form single, double or triple bonds in order to achieve noble gas configurations. Resonance forms are discussed which show that molecules may be represented by multiple equivalent structures. The document then discusses how molecular shape is controlled by valence electron repulsion. Basic reactions like substitution and elimination are also mentioned.
This document discusses standard enthalpies and the Born-Haber cycle. It provides background on the Born-Haber cycle, which is used to calculate lattice energies by comparing the standard enthalpy of formation of an ionic compound to the enthalpies required to make gaseous ions from the elements. The cycle shows each step of forming gaseous ions and combining them to form the solid ionic compound lattice. Factors that increase lattice enthalpy, making it more endothermic, include decreasing ion size and increasing ion charge. Differences between experimental and theoretical lattice energies can indicate covalent character in the bonds.
1. The document discusses alkyl halide reactions including SN1 and SN2 mechanisms. It describes factors that affect the rates of these reactions such as the substrate, leaving group, nucleophile, and solvent.
2. SN1 is a two-step reaction involving a carbocation intermediate. SN2 is a single-step reaction without an intermediate. SN1 reactions result in racemization while SN2 reactions cause inversion of configuration.
3. Tertiary alkyl halides undergo SN1 reactions most readily due to stable carbocation intermediates. Polar protic solvents favor SN1 while polar aprotic solvents favor SN2.
The document discusses different types of substitution reactions including nucleophilic substitution, electrophilic substitution, and free radical substitution. It provides details on the mechanisms, kinetics, stereochemistry and factors affecting the rate of nucleophilic substitution reactions SN1 and SN2. SN1 follows a unimolecular mechanism involving a carbocation intermediate while SN2 follows a bimolecular mechanism with a single concerted transition state. The document also discusses electrophilic aromatic substitution reactions and addition and elimination reactions of alkenes and alkynes.
This document summarizes different types of reactions that alkyl halides undergo: nucleophilic substitution and elimination reactions. It describes the SN2, SN1, E2 and E1 reaction mechanisms in detail. The key points are:
- SN2 is a single-step reaction that proceeds with inversion of configuration. It is sensitive to steric effects.
- SN1 is a two-step reaction involving carbocation formation. It can lead to loss of chirality and is favored for tertiary alkyl halides.
- E2 is a concerted elimination reaction that is stereospecific. E1 proceeds through a carbocation and is not stereospecific.
- The type of reaction depends on the structure
- α-Hydrogens in carbonyl compounds are acidic and can be deprotonated to form enolates using bases like KH or LDA.
- Enolates are nucleophilic and can undergo reactions like alkylation, halogenation, and aldol condensation. They tautomerize between keto and enol forms.
- α,β-Unsaturated carbonyls undergo conjugate additions and other reactions characteristic of alkenes and carbonyl groups. They can rearrange to the thermodynamic enol form.
- α-Hydrogens in carbonyl compounds are acidic and can be deprotonated to form enolates using bases like KH or LDA.
- Enolates are nucleophilic and can undergo reactions like alkylation, halogenation, and aldol condensation. They tautomerize between keto and enol forms.
- α,β-Unsaturated carbonyls undergo conjugate additions and other reactions characteristic of alkenes and carbonyl groups. They can rearrange between β,γ and α,β isomers with acid or base catalysis.
This document discusses suffixes and terminology used in medicine. It begins by listing common combining forms used to build medical terms and their meanings. It then defines several noun, adjective, and shorter suffixes and provides their meanings. Examples are given of medical terms built using combining forms and suffixes. The document also examines specific medical concepts in more depth, such as hernias, blood cells, acromegaly, splenomegaly, and laparoscopy.
The document is a chapter from a medical textbook that discusses anatomical terminology pertaining to the body as a whole. It defines the structural organization of the body from cells to tissues to organs to systems. It also describes the body cavities and identifies the major organs contained within each cavity, as well as anatomical divisions of the abdomen and back.
This document is from a textbook on medical terminology. It discusses the basic structure of medical words and how they are built from prefixes, suffixes, and combining forms. Some key points:
- Medical terms are made up of elements including roots, suffixes, prefixes, and combining vowels. Understanding these elements is important for analyzing terms.
- Common prefixes include hypo-, epi-, and cis-. Common suffixes include -itis, -algia, and -ectomy.
- Dozens of combining forms are provided, such as gastro- meaning stomach, cardi- meaning heart, and aden- meaning gland.
- Rules are provided for analyzing terms, such as reading from the suffix backward and dropping combining vowels before suffixes starting with vowels
This document is the copyright information for Chapter 25 on Cancer from the 6th edition of the textbook Molecular Cell Biology published in 2008 by W. H. Freeman and Company. The chapter was authored by a team that includes Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh, and Matsudaira.
This document is the copyright information for Chapter 24 on Immunology from the 6th edition of the textbook Molecular Cell Biology published in 2008 by W. H. Freeman and Company. The chapter was authored by Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh, and Matsudaira.
Nerve cells, also known as neurons, are highly specialized cells that process and transmit information through electrical and chemical signals. This chapter discusses the structure and function of neurons, how they communicate with each other via synapses, and how signals are propagated along neurons through changes in their membrane potentials. Neurons play a vital role in the nervous system by allowing organisms to process information and coordinate their responses.
This document is the copyright information for Chapter 22 from the 6th edition of the textbook "Molecular Cell Biology" published in 2008 by W. H. Freeman and Company. The chapter is titled "The Molecular Cell Biology of Development" and is authored by Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh, and Matsudaira.
This document is the copyright information for Chapter 21 from the sixth edition of the textbook "Molecular Cell Biology" published in 2008 by W. H. Freeman and Company. The chapter is titled "Cell Birth, Lineage, and Death" and is authored by Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh, and Matsudaira.
This document is the copyright page for Chapter 20 from the 6th edition of the textbook "Molecular Cell Biology" published in 2008 by W. H. Freeman and Company. The chapter is titled "Regulating the Eukaryotic Cell Cycle" and is authored by a group of scientists including Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh, and Matsudaira.
This document is the copyright information for Chapter 19 from the 6th edition textbook "Molecular Cell Biology" published in 2008 by W. H. Freeman and Company. The chapter is titled "Integrating Cells into Tissues" and is authored by Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh, and Matsudaira.
This chapter discusses microtubules and intermediate filaments, which are types of cytoskeletal filaments that help organize and move cellular components. Microtubules are involved in processes like cell division and intracellular transport, while intermediate filaments provide mechanical strength and help integrate the nucleus with the cytoplasm. Together, these filaments play important structural and functional roles in eukaryotic cells.
This chapter discusses microfilaments, which are one of the three main types of cytoskeletal filaments found in eukaryotic cells. Microfilaments are composed of actin filaments and play important roles in cell motility, structure, and intracellular transport. They allow cells to change shape and to move by contracting or extending parts of the cell surface.
This document is the copyright page for Chapter 16 from the 6th edition of the textbook "Molecular Cell Biology" published in 2008 by W. H. Freeman and Company. The chapter is titled "Signaling Pathways that Control Gene Activity" and is authored by a group of scientists including Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh and Matsudaira.
This document is the copyright page for Chapter 15 of the 6th edition textbook "Molecular Cell Biology" by Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh, and Matsudaira. It provides the chapter title "Cell Signaling I: Signal Transduction and Short-Term Cellular Responses" and notes the copyright is held by W. H. Freeman and Company in 2008.
This document is the copyright page for Chapter 14 from the 6th edition textbook "Molecular Cell Biology" published in 2008 by W. H. Freeman and Company. The chapter is titled "Vesicular Traffic, Secretion, and Endocytosis" and is authored by a group of scientists including Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh and Matsudaira.
This chapter discusses how proteins are transported into membranes and organelles within cells. Proteins destined for membranes or organelles have targeting signals that are recognized by transport systems. The transport systems then direct the proteins to their proper destinations, such as inserting membrane proteins into membranes or delivering soluble proteins into organelles.
This document is the copyright information for Chapter 12 from the sixth edition of the textbook "Molecular Cell Biology" published in 2008 by W. H. Freeman and Company. The chapter is titled "Cellular Energetics" and is authored by Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh, and Matsudaira.
This chapter discusses the transmembrane transport of ions and small molecules across cell membranes. It covers topics such as passive transport through membrane channels and pumps, as well as active transport using ATP. The chapter is from the 6th edition of the textbook Molecular Cell Biology and is copyrighted by W. H. Freeman and Company in 2008.
This document is the copyright information for Chapter 10, titled "Biomembrane Structure", from the sixth edition of the textbook "Molecular Cell Biology" published in 2008 by W. H. Freeman and Company. The chapter was written by a team of authors including Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh and Matsudaira.
This document is the copyright information for Chapter 9 from the 6th edition of the textbook "Molecular Cell Biology" published in 2008 by W. H. Freeman and Company. The chapter is titled "Visualizing, Fractionating, and Culturing Cells" and is authored by Lodish, Berk, Kaiser, Krieger, Scott, Bretscher, Ploegh, and Matsudaira.
it describes the bony anatomy including the femoral head , acetabulum, labrum . also discusses the capsule , ligaments . muscle that act on the hip joint and the range of motion are outlined. factors affecting hip joint stability and weight transmission through the joint are summarized.
A review of the growth of the Israel Genealogy Research Association Database Collection for the last 12 months. Our collection is now passed the 3 million mark and still growing. See which archives have contributed the most. See the different types of records we have, and which years have had records added. You can also see what we have for the future.
How to Setup Warehouse & Location in Odoo 17 InventoryCeline George
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Walmart Business+ and Spark Good for Nonprofits.pdfTechSoup
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Spark Good (walmart.com/sparkgood) is a charitable platform that enables nonprofits to receive donations directly from customers and associates.
Answers about how you can do more with Walmart!"
Main Java[All of the Base Concepts}.docxadhitya5119
This is part 1 of my Java Learning Journey. This Contains Custom methods, classes, constructors, packages, multithreading , try- catch block, finally block and more.
Leveraging Generative AI to Drive Nonprofit InnovationTechSoup
In this webinar, participants learned how to utilize Generative AI to streamline operations and elevate member engagement. Amazon Web Service experts provided a customer specific use cases and dived into low/no-code tools that are quick and easy to deploy through Amazon Web Service (AWS.)
Chapter wise All Notes of First year Basic Civil Engineering.pptxDenish Jangid
Chapter wise All Notes of First year Basic Civil Engineering
Syllabus
Chapter-1
Introduction to objective, scope and outcome the subject
Chapter 2
Introduction: Scope and Specialization of Civil Engineering, Role of civil Engineer in Society, Impact of infrastructural development on economy of country.
Chapter 3
Surveying: Object Principles & Types of Surveying; Site Plans, Plans & Maps; Scales & Unit of different Measurements.
Linear Measurements: Instruments used. Linear Measurement by Tape, Ranging out Survey Lines and overcoming Obstructions; Measurements on sloping ground; Tape corrections, conventional symbols. Angular Measurements: Instruments used; Introduction to Compass Surveying, Bearings and Longitude & Latitude of a Line, Introduction to total station.
Levelling: Instrument used Object of levelling, Methods of levelling in brief, and Contour maps.
Chapter 4
Buildings: Selection of site for Buildings, Layout of Building Plan, Types of buildings, Plinth area, carpet area, floor space index, Introduction to building byelaws, concept of sun light & ventilation. Components of Buildings & their functions, Basic concept of R.C.C., Introduction to types of foundation
Chapter 5
Transportation: Introduction to Transportation Engineering; Traffic and Road Safety: Types and Characteristics of Various Modes of Transportation; Various Road Traffic Signs, Causes of Accidents and Road Safety Measures.
Chapter 6
Environmental Engineering: Environmental Pollution, Environmental Acts and Regulations, Functional Concepts of Ecology, Basics of Species, Biodiversity, Ecosystem, Hydrological Cycle; Chemical Cycles: Carbon, Nitrogen & Phosphorus; Energy Flow in Ecosystems.
Water Pollution: Water Quality standards, Introduction to Treatment & Disposal of Waste Water. Reuse and Saving of Water, Rain Water Harvesting. Solid Waste Management: Classification of Solid Waste, Collection, Transportation and Disposal of Solid. Recycling of Solid Waste: Energy Recovery, Sanitary Landfill, On-Site Sanitation. Air & Noise Pollution: Primary and Secondary air pollutants, Harmful effects of Air Pollution, Control of Air Pollution. . Noise Pollution Harmful Effects of noise pollution, control of noise pollution, Global warming & Climate Change, Ozone depletion, Greenhouse effect
Text Books:
1. Palancharmy, Basic Civil Engineering, McGraw Hill publishers.
2. Satheesh Gopi, Basic Civil Engineering, Pearson Publishers.
3. Ketki Rangwala Dalal, Essentials of Civil Engineering, Charotar Publishing House.
4. BCP, Surveying volume 1
How to Manage Your Lost Opportunities in Odoo 17 CRMCeline George
Odoo 17 CRM allows us to track why we lose sales opportunities with "Lost Reasons." This helps analyze our sales process and identify areas for improvement. Here's how to configure lost reasons in Odoo 17 CRM
1. Chapter 14Chapter 14
Delocalized Pi SystemsDelocalized Pi Systems
TrigonalTrigonal
TheThe ππ bond is ebond is e--
rich:rich: EE++
attackattack,,
R∙R∙
addadd))
The lobes of theThe lobes of the pp--
orbitals:orbitals:
PerpendicularPerpendicular to theto the
sigma frame andsigma frame and
Recall the double bondRecall the double bond
2. 2-Propenyl (Allyl)2-Propenyl (Allyl)
Question:Question: What about adding aWhat about adding a thirdthird
pp-orbital adjacent to the double bond?-orbital adjacent to the double bond?
Is there something special?Is there something special?
Or: Is there any specialOr: Is there any special
reactivity at the carbonsreactivity at the carbons
adjacent to a double bond?adjacent to a double bond?
H
3. a.a.
b.b.
c.c.
SSNN1 reactivity of allylic carbon like that1 reactivity of allylic carbon like that
of Rof RsecsecX,X, even though it is primary!even though it is primary!
ppKKaa ~ 40:~ 40: Acidic!Acidic! 5050
SSNN11
87 kcal mol87 kcal mol-1-1
:: Weak!Weak! 101 kcal mol101 kcal mol-1-1
Replacing one of the hydrogens in ethene withReplacing one of the hydrogens in ethene with
anotheranother spsp22
-hybridized carbon gives an-hybridized carbon gives an allylicallylic
system.system.
Allylic positionAllylic position
Observations:Observations:
H
L
H
B B
H
H
5. MO Picture of 2-PropenylMO Picture of 2-Propenyl
(Allyl)(Allyl)
33 ppOs 3 MOsOs 3 MOs
RecallRecall: Bonds made by overlap: Bonds made by overlap
HH .. HH .. H HH H++
++HH ++ ++HH ++HH++HH
In phaseIn phase
++HH ++ --HH --HH++HH
Out ofOut of
phasephase
BondingBonding
Anti-Anti-
bondingbonding
NodeNode
Sign of the wave function,Sign of the wave function,
Not charge!Not charge!
EE
6. EE
ππ
σσ
σσ**
ππ**
CH2 CH2
What happens to this pictureWhat happens to this picture
when we interact with anotherwhen we interact with another
pp orbital?orbital?
7. 1)1) Interaction with theInteraction with the ππ
bonding orbital causesbonding orbital causes
energy splitting: theenergy splitting: the pp
orbital level moves up andorbital level moves up and
thethe ππ bonding level movesbonding level moves
down.down.
2)2) Interaction with theInteraction with the ππ
antibonding orbital causesantibonding orbital causes
the energy level of thethe energy level of the pp
orbital to move down toorbital to move down to
where it was originally andwhere it was originally and
the energy level of thethe energy level of the ππ
antibonding orbital to moveantibonding orbital to move
up. The two effects on theup. The two effects on the pp
orbital cancel each otherorbital cancel each other
out and the twoout and the two ππ orbitalsorbitals
are pushed apart.are pushed apart.
Interactions of a singly occupiedInteractions of a singly occupied pp--
orbital with each of theorbital with each of the ππ molecularmolecular
orbitalsorbitals
pp
EE
ππ
ππ**
00
ππ
ππ** upup
downdown
unchangedunchanged
EtheneEthene AllylAllyl pp OrbitalOrbital
NonbondingNonbonding
MOMO
8. H2C
H
C
CH2
pp
EE
# of e# of e
dependsdepends
onon ++,,∙∙,,--
ππ
ππ**
00
Resulting picture:Resulting picture:
AndAnd
locationlocation
atat
terminitermini
10. Termination:Termination:
3.3.
BrBr .. ++
..CHCH22CH CHCH CH22 BrCHBrCH22CH CHCH CH22
BrBr .. BrBr ..++ BrBr22
CHCH22CH CHCH CH22
..22 CHCH22CH CHCH CH22CHCH22 CHCHCHCH22
Anything that traps radicals, including the “dirt”Anything that traps radicals, including the “dirt”
on the walls of the flask, contributes toon the walls of the flask, contributes to
termination.termination.
12. Propene generates a symmetrical allylic radical,Propene generates a symmetrical allylic radical,
but this is not always the case. Forbut this is not always the case. For
unsymmetrical systems: mixtures. Ratiosunsymmetrical systems: mixtures. Ratios
depend on % radical character on each carbondepend on % radical character on each carbon
and TSs leading to products.and TSs leading to products.
Br2
Br· +
13. B. SB. SNN1: The Allylic Cation is Stabilized1: The Allylic Cation is Stabilized
CHCH33CH CHCHCH CHCH22ClCl
HH22OO
-- ClCl
--
CHCH33CH CH CHCH CH CH22
++
CHCH33CH CH CHCH CH CH22
++
CHCH33CH CHCHCH CHCH22OHOH CHCH33CHCH CHCHCH CH22
OHOH
fastfastslowslow
ThermodynamicThermodynamic
productproduct
Kinetic productKinetic product
ThermodynamicThermodynamic
KineticKinetic
CationCation
EE
14. C. SC. SNN2: The Allylic TS is Stabilized2: The Allylic TS is Stabilized
CHCH33CH CHCHCH CHCH22ClCl NaNaII CHCH33CH CHCH CH CC
ClCl
II
..
++
‡‡
CHCH33CH CHCHCH CHCH22II ++ ClCl
--
100 times faster100 times faster
thanthan Cl
....
δδ--
δδ--
15. D. Allylic OrganometallicsD. Allylic Organometallics
Li
CH3
CH3
++ RXRX
Allylic Grignard reagents:Allylic Grignard reagents:
Br MgMg++
X
Neutral analogs of allylic anions:Neutral analogs of allylic anions:
NMR shielded!NMR shielded!
X = OR, SR, NRX = OR, SR, NR22
H2C C
CH3
CH2
Li
H2C C
CH3
CH2R
MgBr
X
20. NMRNMR
H H
H
H
JJ = 10= 10
δδ = 5.06= 5.06
δδ = 6.27= 6.27 (effect of 2(effect of 2ndnd
double bond)double bond)
JJ ~1-2~1-2
δδ = 5.16= 5.16
JJtranstrans = 17= 17
JJciscis = 10= 10
H H
H
H
137.2137.2
116.6116.6
21. ConjugationConjugation stabilizes thermodynamically, but it also increasesstabilizes thermodynamically, but it also increases
reactivity, for example inreactivity, for example in electrophilic additionselectrophilic additions (review Chapter 12).(review Chapter 12).
1,2-Addition1,2-Addition
(kinetic)(kinetic)
Intermediate cation is also stabilizedIntermediate cation is also stabilized
++ HClHCl
ClCl
-- 1,4-Addition1,4-Addition
(thermodynamic)(thermodynamic)
CH3
ClCl CH3
ClCl
CH3
CH3
ClCl
--
+ cis+ cis
HClAddnHClAddn
24. Extended ConjugationExtended Conjugation
Thermo 1Thermo 1
Thermo 2Thermo 2
KineticKinetic
++ HHBrBr
BrBr--
Three productsThree products
CH3
CH3
CH3
Quite reactiveQuite reactive
The more double bonds, the more sensitiveThe more double bonds, the more sensitive
(reactive) is the polyene.(reactive) is the polyene.
25. Cyclohexatriene is Special -Cyclohexatriene is Special -
BenzeneBenzene
Cyclic arrayCyclic array ofof six electronssix electrons has special stability,has special stability,
calledcalled aromaticityaromaticity (Chapter 15).(Chapter 15).
Benzene is relatively inert to HBenzene is relatively inert to H22-cat, electrophiles,-cat, electrophiles,
oxidants, in comparison with hexatriene.oxidants, in comparison with hexatriene.
26. Extended Conjugation in NaturalExtended Conjugation in Natural
and Unnatural Productsand Unnatural Products
Orange color of carrotsOrange color of carrots
BiologicalBiological
degradationdegradation
VisionVision
29. Conjugated Systems UndergoConjugated Systems Undergo
Special Transformations:Special Transformations:
Pericyclic ReactionsPericyclic Reactions
The conjugatedThe conjugated ππ system can react as a unit,system can react as a unit,
involvinginvolving both endsboth ends. For example,. For example,
1. Cycloadditions:1. Cycloadditions: TheThe Diels-Alder reaction,Diels-Alder reaction,
a [4+2] cycloadditiona [4+2] cycloaddition
++
ΔΔ
44ππ-4C-4C
DieneDiene
22ππ-2C-2C
DienophileDienophile
20%20%
CycloadductCycloadduct
HC
HC
CH2
CH2
H2
C
C
H2
HC
CH2
HC
CH2
CH2
CH2
30. Diels-Alder reactions work best when we pair anDiels-Alder reactions work best when we pair an
e-riche-rich (push)(push) dienediene with anwith an e-poore-poor (pull)(pull) dienophiledienophile
e-poor dienee-poor diene with anwith an e-rich dienophilee-rich dienophile
or anor an
The Diels-Alder Reaction isThe Diels-Alder Reaction is
ChemoselectiveChemoselective
Depends on substituents:Depends on substituents:
e-Donating:e-Donating: Alkyl, alkoxy, alkylthioAlkyl, alkoxy, alkylthio
CHCH33,, CHCH33O,O, CHCH33CHCH22SS
HyperconjugationHyperconjugation
ResonanceResonance
Even though O is e-negative (inductive effect), resonance wins out.Even though O is e-negative (inductive effect), resonance wins out.
OCH3 OCH3 OCH3
31. e-Withdrawing:e-Withdrawing: CFCF33, CR, C N, NO, CR, C N, NO22
OO
Resonance:Resonance:
Example:Example:
Inductive:Inductive:
Does not compete with dienophileDoes not compete with dienophile
90%90%
++
ΔΔ
C
F
F
F
H2C C
CR
H
O
H2C C
CR
H
O
H2C C
CR
H
O
CR
O
CR
O
37. Alkynes as DienophilesAlkynes as Dienophiles
Generates 1,4-cyclohexadienesGenerates 1,4-cyclohexadienes
CO2CH3
CO2CH3
CO2CH3
CO2CH3
++
Can reactCan react
againagain
75%75%
CO2CH3
CO2CH3
38. ΔΔ
ΔΔ
hhυυ
ExothermicExothermic
(ring strain(ring strain
released)released) Light driven:Light driven: Can beat thermodynamicsCan beat thermodynamics..
Wavelength dependent (can go either way).Wavelength dependent (can go either way).ΔΔH °H ° = -9.7 kcal mol= -9.7 kcal mol-1-1
ExothermicExothermic
(C C better than C C, unless ring strain present)(C C better than C C, unless ring strain present)
ΔΔH °H ° = -14.7 kcal mol= -14.7 kcal mol-1-1
hhυυ
2. Electrocyclic Reactions:2. Electrocyclic Reactions:
Intramolecular ring closure and openingsIntramolecular ring closure and openings
43. ΔΔ = dis= dis
Even more startling: The hexatriene/cyclohexadieneEven more startling: The hexatriene/cyclohexadiene
interconversion is alsointerconversion is also stereospecific,stereospecific, but follows thebut follows the
oppositeopposite rules of sense of rotation, compared torules of sense of rotation, compared to
butadiene/cyclobutene system:butadiene/cyclobutene system:
45. Orbital Symmetry: An inkling of how this might go……Orbital Symmetry: An inkling of how this might go……
Conrotatory
Disrotatory
Controls thermalControls thermal
closureclosure
Controls photo-Controls photo-
chemical closurechemical closure
hhνν-provides e to-provides e to ππ33
The orbital signs at theThe orbital signs at the
termini alternate with #termini alternate with #
of double bonds.of double bonds.
47. UV-Vis spectroscopy requires much higher energy thanUV-Vis spectroscopy requires much higher energy than
NMR (kcals vs calories), does not need external “condition”NMR (kcals vs calories), does not need external “condition”
(magnet), built into molecule: electronic excitation from(magnet), built into molecule: electronic excitation from
bonding to antibonding levels, particularly easy forbonding to antibonding levels, particularly easy for ππ
systems, because occupiedsystems, because occupiedunoccupiedunoccupied ΔΔEE relatively small.relatively small.
NoNo ππ bond left!bond left!
Light causesLight causes
cis-transcis-trans
isomerization,isomerization,
radicalradical
reactionsreactions
SimpleSimple ππ bond, as in ethene:bond, as in ethene:
48. Spectrum of EtheneSpectrum of Ethene
Quoted asQuoted as λλmaxmax
Broad, because of rotational andBroad, because of rotational and
vibrational states. Electronicvibrational states. Electronic
spectroscopy is fast, nospectroscopy is fast, no
“averaging”“averaging”AA
171 nm171 nm
WavelengthWavelength λλ (given in(given in nmnm, units of 10, units of 10-9-9
m; not in frequencym; not in frequency
υυ = c/= c/λλ,, as we did in NMR, whereas we did in NMR, where λλ ~ 100 mm to 1m!)~ 100 mm to 1m!)
49. UV spectroscopy below 200 nm requires vacuum,UV spectroscopy below 200 nm requires vacuum,
because air absorbs. Normally (in atmosphere) one scansbecause air absorbs. Normally (in atmosphere) one scans
200-400 (UV), 400-800 nm (visible). This allows lower200-400 (UV), 400-800 nm (visible). This allows lower
energy tranisitons to be recorded, e.g. 1,3-butadiene:energy tranisitons to be recorded, e.g. 1,3-butadiene:
εε == AA//cc
EE
RelativelyRelatively
lowlow
energyenergy
Shoulder, sh
Peak heights are reported asPeak heights are reported as
εε :: Extinction coefficientExtinction coefficient,,
which iswhich is absorbanceabsorbance
normalized bynormalized by concentrationconcentration::
λmax
λλmaxmax = 222.5 nm (εε == 10,800)
50. AbsorptionAbsorption
in thein the
visiblevisible
450 nm450 nm orangeorange--redred
550 nm550 nm violetviolet
650 nm650 nm blueblue--greengreen
Color ofColor of
substancesubstance
Visible Absorption:Visible Absorption:
ColorColor
Light enters the prism from the top
right, and is refracted by the glass.
The violet is bent more than the
yellow and red, so the colors separate.
NewtonNewton
51. In extendedIn extended ππ systems many transitions aresystems many transitions are
possible, giving rise to more complex and notpossible, giving rise to more complex and not
readily interpretable spectra, but HOMO-LUMOreadily interpretable spectra, but HOMO-LUMO
gap gets smaller: Longest wavelength absorptiongap gets smaller: Longest wavelength absorption
is indicative of theis indicative of the extentextent of conjugation, e.g.of conjugation, e.g.
CH3
λλ max = 271 nmmax = 271 nm
ConjugatedConjugated
λλ max = 217 nmmax = 217 nm
UnconjugatedUnconjugated
Greater conjugation:Greater conjugation:
Smaller HOMO/LUMO gapSmaller HOMO/LUMO gap