This document provides an introduction to stereochemistry. It discusses the scope of stereochemistry, which includes static stereochemistry dealing with stereoisomers and their properties, and dynamic stereochemistry dealing with stereochemical outcomes of reactions. The history of stereochemistry is outlined, beginning with the discovery of plane-polarized light in the early 1800s by scientists like Malus and Biot, culminating in Pasteur's separation of tartaric acid crystals and establishing the concept of chirality in 1848. Key concepts introduced include chiral and achiral molecules, ordinary and plane-polarized light, and different types of isomers such as constitutional/structural isomers and stereoisomers.
Chain reactions involve reactive intermediates called chain carriers that propagate the reaction by producing more reactive intermediates. Chain reactions consist of initiation, propagation, and termination steps. The initiation step produces the first reactive intermediates. The propagation step produces more reactive intermediates from reaction of the previous intermediates. Termination stops the chain by deactivating the chain carriers. Chain reactions for forming HCl can occur thermally or photochemically. In the photochemical reaction, light initiates the production of chlorine atoms from Cl2, which then react with H2 through a series of propagation and termination steps to ultimately form HCl. The presence of oxygen complicates the reaction mechanism.
This document discusses various spectral methods used to analyze polymer structure, including infrared spectroscopy, Raman spectroscopy, UV-visible spectroscopy, NMR spectroscopy, and X-ray spectroscopy. Infrared spectroscopy identifies chemical bonds and structures based on vibrational transitions. Raman spectroscopy detects symmetric vibrational modes and is useful for conformational studies. UV-visible spectroscopy identifies impurities based on electronic transitions. NMR spectroscopy determines proton environments and stereochemistry. X-ray spectroscopy identifies crystalline structure through diffraction patterns. These spectral methods provide information on polymer morphology, structure, and composition.
This document describes the preparation of p-nitro acetanilide from acetanilide. Acetanilide is nitrated using nitric and sulfuric acid. This produces p-nitro acetanilide as the major product along with a minor amount of o-nitro acetanilide. The p-nitro acetanilide product is purified by recrystallization from ethanol, yielding colorless crystals. Percent yield of the product is calculated and the melting point is obtained and compared to literature values.
Basic inorganic chemistry part 2 organometallic chemistryssuser50a397
The document provides an overview of organometallic chemistry including:
- Key concepts such as the 18 electron rule, metal carbonyls, and sandwich compounds.
- Important discoveries such as Zeise's salt (first transition metal organometallic compound) and ferrocene (first sandwich compound).
- Industrial applications of organometallic catalysts in homogeneous catalysis including hydroformylation and hydrocarbon conversions.
- Methods for counting electrons in organometallic complexes using the neutral atom and oxidation state methods.
Nucleophilic aromatic substitution is a reaction where a nucleophile displaces a good leaving group such as a halide on an aromatic ring. The document discusses several mechanisms for nucleophilic aromatic substitution including SNAr, SN1, benzyne, SRN1, and examples like the Von Richter and Smiles rearrangements. The rate is facilitated by electron-withdrawing groups on the aromatic ring that stabilize the cyclohexadienyl anion intermediate.
Thermogravimetric analysis (TGA) measures the change in weight of a sample as it is heated. It can be used to detect decomposition, oxidation, and solvent loss. Some key applications of TGA include analyzing ceramics, metals, polymers, pharmaceuticals, foods, and printed circuit boards. For example, TGA can measure the thermal stability and oxidation kinetics of ceramic materials like silicon carbide, determine the composition of metal alloys, and analyze the effects of additives and optimization of polymer materials.
The document discusses the Octant Rule, which relates the sign and intensity of the cotton effect exhibited by optically active saturated ketones to the spatial orientation of atoms around the carbonyl group.
The Octant Rule states that substituents in the back upper left and back lower right octants make a positive contribution to the cotton effect, while those in the upper right and back lower left octants make a negative contribution. Substituents in the nodal planes make no contribution.
The rule can be used to predict the sign of the cotton effect, determine stereochemistry, and study conformational mobility in compounds. Examples of chiral ketones are analyzed using octant diagrams to show how the rule is applied.
These are chemical shift reagents and solvent induced shifts have their application in resolving the NMR Spectra of complex structures by inducing shift with respect to reference compound. Thus useful in interpretation of structures of complex organic compounds.
Chain reactions involve reactive intermediates called chain carriers that propagate the reaction by producing more reactive intermediates. Chain reactions consist of initiation, propagation, and termination steps. The initiation step produces the first reactive intermediates. The propagation step produces more reactive intermediates from reaction of the previous intermediates. Termination stops the chain by deactivating the chain carriers. Chain reactions for forming HCl can occur thermally or photochemically. In the photochemical reaction, light initiates the production of chlorine atoms from Cl2, which then react with H2 through a series of propagation and termination steps to ultimately form HCl. The presence of oxygen complicates the reaction mechanism.
This document discusses various spectral methods used to analyze polymer structure, including infrared spectroscopy, Raman spectroscopy, UV-visible spectroscopy, NMR spectroscopy, and X-ray spectroscopy. Infrared spectroscopy identifies chemical bonds and structures based on vibrational transitions. Raman spectroscopy detects symmetric vibrational modes and is useful for conformational studies. UV-visible spectroscopy identifies impurities based on electronic transitions. NMR spectroscopy determines proton environments and stereochemistry. X-ray spectroscopy identifies crystalline structure through diffraction patterns. These spectral methods provide information on polymer morphology, structure, and composition.
This document describes the preparation of p-nitro acetanilide from acetanilide. Acetanilide is nitrated using nitric and sulfuric acid. This produces p-nitro acetanilide as the major product along with a minor amount of o-nitro acetanilide. The p-nitro acetanilide product is purified by recrystallization from ethanol, yielding colorless crystals. Percent yield of the product is calculated and the melting point is obtained and compared to literature values.
Basic inorganic chemistry part 2 organometallic chemistryssuser50a397
The document provides an overview of organometallic chemistry including:
- Key concepts such as the 18 electron rule, metal carbonyls, and sandwich compounds.
- Important discoveries such as Zeise's salt (first transition metal organometallic compound) and ferrocene (first sandwich compound).
- Industrial applications of organometallic catalysts in homogeneous catalysis including hydroformylation and hydrocarbon conversions.
- Methods for counting electrons in organometallic complexes using the neutral atom and oxidation state methods.
Nucleophilic aromatic substitution is a reaction where a nucleophile displaces a good leaving group such as a halide on an aromatic ring. The document discusses several mechanisms for nucleophilic aromatic substitution including SNAr, SN1, benzyne, SRN1, and examples like the Von Richter and Smiles rearrangements. The rate is facilitated by electron-withdrawing groups on the aromatic ring that stabilize the cyclohexadienyl anion intermediate.
Thermogravimetric analysis (TGA) measures the change in weight of a sample as it is heated. It can be used to detect decomposition, oxidation, and solvent loss. Some key applications of TGA include analyzing ceramics, metals, polymers, pharmaceuticals, foods, and printed circuit boards. For example, TGA can measure the thermal stability and oxidation kinetics of ceramic materials like silicon carbide, determine the composition of metal alloys, and analyze the effects of additives and optimization of polymer materials.
The document discusses the Octant Rule, which relates the sign and intensity of the cotton effect exhibited by optically active saturated ketones to the spatial orientation of atoms around the carbonyl group.
The Octant Rule states that substituents in the back upper left and back lower right octants make a positive contribution to the cotton effect, while those in the upper right and back lower left octants make a negative contribution. Substituents in the nodal planes make no contribution.
The rule can be used to predict the sign of the cotton effect, determine stereochemistry, and study conformational mobility in compounds. Examples of chiral ketones are analyzed using octant diagrams to show how the rule is applied.
These are chemical shift reagents and solvent induced shifts have their application in resolving the NMR Spectra of complex structures by inducing shift with respect to reference compound. Thus useful in interpretation of structures of complex organic compounds.
This document discusses theories of unimolecular reaction kinetics, including the Lindemann-Christiansen theory, Hinshelwood theory, RRK theory, and RRKM theory. It notes limitations of earlier theories in explaining experimental data. The RRKM theory, developed by Marcus in 1951-1952, redefined the RRK treatment and addressed prior limitations. RRKM theory is now widely used to interpret thermal and photochemical reactions and allows calculating reaction rates from known vibrational frequencies of molecules.
Crown ethers are cyclic chemical compounds consisting of a ring containing several ether groups. Common crown ethers include tetramer, pentamer, and hexamer of ethylene oxide. The term "crown" refers to their resemblance to a crown sitting on a person's head when bound to a cation. Crown ethers have applications in synthesis such as esterification and aromatic substitution reactions. They also have analytical applications such as determination of metals in geological samples and use as phase transfer catalysts.
Solid State Synthesis of Mixed-Metal Oxidesanthonyhr
The document discusses solid-state synthesis of mixed metal oxides. It introduces solid state chemistry and synthesis, which involves producing solids by combining substances through high-temperature reactions. Specific aims are to synthesize new mixed metal oxide compounds with distinct properties for various applications. The methodology described involves using silica tubes lined with carbon and heating powdered metal reactants at high temperatures for 1-2 weeks to form novel crystals. Future work plans to carry out reactions combining tin, lead, antimony and bismuth, and synthesize new mixed metal oxides according to predicted products.
C13 NMR spectroscopy provides information about carbon atoms in molecules. It works based on the absorption of radio waves by carbon-13 nuclei in a magnetic field. There are a few key points:
1) C13 NMR is difficult to analyze due to the low natural abundance of C13 and its weaker magnetic resonance compared to protons.
2) Different types of carbon atoms (CH, CH2, CH3) can be distinguished based on their chemical shifts and coupling patterns. Proton decoupling is used to simplify spectra.
3) DEPT experiments analyze carbon types by enhancing signals from different hybridized carbons (CH, CH2, CH3) in different ways. This allows determining the number and type
This document provides procedures for preparing several transition metal complexes. It describes preparing hexaamminecobalt(III)chloride from cobaltous chloride hexahydrate and ammonium chloride. It also describes preparing hexaamminenickel(II)chloride from nickel chloride hexahydrate and aqueous ammonia, as well as potassium tris(oxalato)ferrate(III) trihydrate from ferrous ammonium sulfate and oxalic acid. The document gives the name, structure, properties and theoretical yield calculations for each complex prepared.
The document discusses charge transfer complexes and the different types of charge transfer that can cause color in transition metal complexes. It explains that ligand to metal charge transfer and metal to ligand charge transfer can produce color when pi donor or accepting ligands are present with metals lacking or having low oxidation state d-electrons, respectively. As an example, it describes the metal to ligand charge transfer observed in the spectra of the tris(bipyridine)ruthenium(II) dichloride complex.
This document discusses the gas adsorption technique for determining surface area of solids. It works based on the BET theory of gas molecules physically adsorbing onto surfaces. The technique involves pretreating a solid sample under heat and vacuum to remove contaminants, then exposing it to incremental doses of an adsorptive gas like nitrogen at cryogenic temperatures. By measuring the quantity of gas adsorbed at each pressure, an adsorption isotherm can be generated to determine the monolayer capacity and calculate the surface area based on the area each adsorbed gas molecule covers. The gas adsorption technique can measure pores between 0.4-50nm and is an established, easy method for surface area analysis.
C13 NMR spectroscopy provides information about carbon structures. It detects the less abundant C13 isotope. Though less sensitive than proton NMR, C13 NMR spectra are easier to interpret due to fewer splitting patterns. Each non-equivalent carbon absorbs at a different chemical shift depending on its electronic environment. Chemical shifts typically range from 0-250 ppm downfield from TMS. Factors like hybridization, electronegativity of substituents, and substituent effects influence the chemical shift. C13 NMR is useful for determining carbon skeletons and functional groups.
Thermal analysis techniques such as differential thermal analysis (DTA) measure the temperature difference between a sample and an inert reference material as they undergo identical thermal cycles. DTA provides information about physical and chemical changes in a material as it is heated, such as melting, crystallization, and decomposition, by detecting endothermic or exothermic reactions. The DTA instrument consists of sample and reference holders connected to thermocouples within a furnace. Changes in the sample are detected as differences in temperature compared to the unreactive reference. DTA is useful for characterizing materials like minerals, polymers, and pharmaceuticals.
The document discusses protecting groups, focusing on protecting alcohols. It defines protecting groups as functional groups that are stable to reaction conditions but can be easily removed to regenerate the original functional group. The document outlines criteria for protecting groups and then discusses various methods for protecting alcohols, including using acetals, ethers, and silyl ethers. It provides examples of specific protecting groups like THP, MEM, benzyl ethers, and trialkylsilyl ethers.
This document summarizes the principles and applications of Mossbauer spectroscopy, also known as nuclear gamma resonance spectroscopy. It discusses how Mossbauer spectroscopy probes nuclei using gamma rays and measures gamma absorption spectra. It explains how nuclei in solid crystals can undergo nuclear resonance because they are bound and not free to recoil. The document also outlines several key parameters that must be satisfied for Mossbauer spectroscopy to be effective, including the energy of nuclear transitions and lifetimes of excited states. Finally, it provides examples of how Mossbauer spectroscopy has been used to identify iron oxide nanoparticles in magnetotactic bacteria.
This document discusses proton magnetic resonance spectroscopy (NMR spectroscopy), specifically focusing on spin-spin coupling, coupling constants, and the different types of coupling that can occur including geminal, vicinal, and long range coupling. It explains that the coupling constant value increases with increasing bond angle and electronegativity. It also discusses first order spectra and provides examples of geminal, vicinal, and long range coupling, as well as factors that affect coupling constant values.
Photochemistry is the branch of chemistry concerned with chemical reactions caused by light absorption. Photochemical reactions proceed differently than thermal reactions and can form thermodynamically disfavored products or overcome large activation barriers. When a molecule absorbs light, it is elevated to an excited state. The Grotthuss–Draper law states that light must be absorbed for a photochemical reaction to occur. Absorbed light can excite a molecule to different singlet or triplet states, which can then relax through radiationless or radiative processes like fluorescence or phosphorescence. Experimental factors like light sources, reactors, solvents, and wavelength selection influence photochemical reactions.
This document discusses double resonance in nuclear magnetic resonance (NMR) spectroscopy. It explains spin decoupling techniques that are used to simplify complex NMR spectra. By irradiating coupled protons, decoupling can eliminate splitting of signals and cause multiplets to collapse into doublets or singlets. This produces easier to interpret spectra. Decoupling is demonstrated on an ethanol sample, where exchanging hydrogens for deuterium causes signals to disappear. Irradiating methyl hydrogens in a molecule can also simplify signals by removing coupling to adjacent protons. Decoupling enhances spectral signals and allows clearer distinction between them.
This document provides an overview of Fourier transform infrared (FT-IR) spectroscopy. It discusses the electromagnetic spectrum and how infrared radiation lies between visible light and microwaves. Infrared spectroscopy works by detecting the vibrations of bonds between atoms in molecules as they absorb infrared light. An FT-IR uses an interferometer to measure an infrared spectrum with advantages of high sensitivity, accuracy, and resolution compared to other methods. The document outlines applications of infrared spectroscopy such as pharmaceutical analysis and environmental monitoring.
The document introduces the Heck reaction, which is a coupling reaction where a metal catalyst aids in coupling two hydrocarbon fragments. Specifically, the Heck reaction involves converting a terminal alkene to an internal alkene. Richard Heck, Ei-ichi Negishi, and Akira Suzuki were jointly awarded the Nobel Prize in 2010 for their work developing palladium-catalyzed C-C cross coupling reactions, including the Heck reaction. The mechanism of the Heck reaction involves oxidative addition, insertion, β-H elimination, and reductive elimination steps.
The document discusses nuclear magnetic resonance (NMR) spectroscopy, specifically proton (1H) and carbon-13 (13C) NMR. It provides information on why NMR is used, the types of information it can provide about compounds, and the physical properties of 1H and 13C nuclei that influence their NMR spectra. It also discusses factors that affect chemical shifts, common chemical shift ranges, coupling behaviors, and how to determine the number of signals expected for given compounds from their carbon environments. The document aims to explain the fundamentals and applications of 1H and 13C NMR spectroscopy.
Mossbauer spectroscopy involves the resonant absorption of gamma rays by atomic nuclei. It was first observed by Mossbauer in 1958, for which he received the Nobel Prize. The basic principles are that nuclei emitting gamma rays lose a small amount of energy to recoil, while absorbing nuclei must have slightly higher energy for resonance to occur. Doppler shift is used to scan the gamma ray energy through a range and bring the source and sample nuclei into resonance by accelerating the source. The technique provides information about oxidation states, spin states, and local environments of atoms in samples.
The document summarizes the Tiffeneau–Demjanov rearrangement reaction. It was discovered in the early 1900s by French chemist Marc Émile Pierre Adolphe Tiffeneau and Russian chemist Nikolay Yakovlevich Demyanov. The reaction involves treating 1-aminomethyl-cycloalkanol with nitrous acid to form an enlarged cycloketone through a 1,2-carbon migration. This ring expansion reaction is useful for increasing the size of amino-substituted cyclic compounds from four to eight-membered rings. The mechanism involves diazotization of the amine to form a diazonium ion that undergoes 1,2-alkyl shift accompanied by nitrogen loss to form
This document provides an overview of stereochemistry. It discusses the history of stereochemistry beginning with Pasteur's discovery of optical isomerism in tartaric acid in 1849. Van't Hoff and LeBel later explained optical activity in terms of tetrahedral carbon atom arrangements. The document defines types of stereoisomers including enantiomers, which are non-superimposable mirror images, and diastereomers. It also discusses concepts like chirality, optical activity, and racemic mixtures. Baeyer strain theory is explained as it relates to stability and reactivity of cycloalkanes based on bond angle deviations from ideal values. Conformational analysis of ethane and cyclohexane are also summarized.
This document discusses different types of isomerism in organic chemistry, including structural isomerism, stereoisomerism, and optical isomerism. It defines isomerism as compounds with the same molecular formula but different properties. The main types of structural isomerism are chain, position, functional, metamerism, and tautomerism. Stereoisomerism includes conformational and configurational isomers, with the latter including optical isomers and geometric isomers. Optical activity and how it relates to chirality and asymmetric carbons is also explained. Different projection formulas used to depict three-dimensional chiral molecules in two dimensions are also presented.
This document discusses theories of unimolecular reaction kinetics, including the Lindemann-Christiansen theory, Hinshelwood theory, RRK theory, and RRKM theory. It notes limitations of earlier theories in explaining experimental data. The RRKM theory, developed by Marcus in 1951-1952, redefined the RRK treatment and addressed prior limitations. RRKM theory is now widely used to interpret thermal and photochemical reactions and allows calculating reaction rates from known vibrational frequencies of molecules.
Crown ethers are cyclic chemical compounds consisting of a ring containing several ether groups. Common crown ethers include tetramer, pentamer, and hexamer of ethylene oxide. The term "crown" refers to their resemblance to a crown sitting on a person's head when bound to a cation. Crown ethers have applications in synthesis such as esterification and aromatic substitution reactions. They also have analytical applications such as determination of metals in geological samples and use as phase transfer catalysts.
Solid State Synthesis of Mixed-Metal Oxidesanthonyhr
The document discusses solid-state synthesis of mixed metal oxides. It introduces solid state chemistry and synthesis, which involves producing solids by combining substances through high-temperature reactions. Specific aims are to synthesize new mixed metal oxide compounds with distinct properties for various applications. The methodology described involves using silica tubes lined with carbon and heating powdered metal reactants at high temperatures for 1-2 weeks to form novel crystals. Future work plans to carry out reactions combining tin, lead, antimony and bismuth, and synthesize new mixed metal oxides according to predicted products.
C13 NMR spectroscopy provides information about carbon atoms in molecules. It works based on the absorption of radio waves by carbon-13 nuclei in a magnetic field. There are a few key points:
1) C13 NMR is difficult to analyze due to the low natural abundance of C13 and its weaker magnetic resonance compared to protons.
2) Different types of carbon atoms (CH, CH2, CH3) can be distinguished based on their chemical shifts and coupling patterns. Proton decoupling is used to simplify spectra.
3) DEPT experiments analyze carbon types by enhancing signals from different hybridized carbons (CH, CH2, CH3) in different ways. This allows determining the number and type
This document provides procedures for preparing several transition metal complexes. It describes preparing hexaamminecobalt(III)chloride from cobaltous chloride hexahydrate and ammonium chloride. It also describes preparing hexaamminenickel(II)chloride from nickel chloride hexahydrate and aqueous ammonia, as well as potassium tris(oxalato)ferrate(III) trihydrate from ferrous ammonium sulfate and oxalic acid. The document gives the name, structure, properties and theoretical yield calculations for each complex prepared.
The document discusses charge transfer complexes and the different types of charge transfer that can cause color in transition metal complexes. It explains that ligand to metal charge transfer and metal to ligand charge transfer can produce color when pi donor or accepting ligands are present with metals lacking or having low oxidation state d-electrons, respectively. As an example, it describes the metal to ligand charge transfer observed in the spectra of the tris(bipyridine)ruthenium(II) dichloride complex.
This document discusses the gas adsorption technique for determining surface area of solids. It works based on the BET theory of gas molecules physically adsorbing onto surfaces. The technique involves pretreating a solid sample under heat and vacuum to remove contaminants, then exposing it to incremental doses of an adsorptive gas like nitrogen at cryogenic temperatures. By measuring the quantity of gas adsorbed at each pressure, an adsorption isotherm can be generated to determine the monolayer capacity and calculate the surface area based on the area each adsorbed gas molecule covers. The gas adsorption technique can measure pores between 0.4-50nm and is an established, easy method for surface area analysis.
C13 NMR spectroscopy provides information about carbon structures. It detects the less abundant C13 isotope. Though less sensitive than proton NMR, C13 NMR spectra are easier to interpret due to fewer splitting patterns. Each non-equivalent carbon absorbs at a different chemical shift depending on its electronic environment. Chemical shifts typically range from 0-250 ppm downfield from TMS. Factors like hybridization, electronegativity of substituents, and substituent effects influence the chemical shift. C13 NMR is useful for determining carbon skeletons and functional groups.
Thermal analysis techniques such as differential thermal analysis (DTA) measure the temperature difference between a sample and an inert reference material as they undergo identical thermal cycles. DTA provides information about physical and chemical changes in a material as it is heated, such as melting, crystallization, and decomposition, by detecting endothermic or exothermic reactions. The DTA instrument consists of sample and reference holders connected to thermocouples within a furnace. Changes in the sample are detected as differences in temperature compared to the unreactive reference. DTA is useful for characterizing materials like minerals, polymers, and pharmaceuticals.
The document discusses protecting groups, focusing on protecting alcohols. It defines protecting groups as functional groups that are stable to reaction conditions but can be easily removed to regenerate the original functional group. The document outlines criteria for protecting groups and then discusses various methods for protecting alcohols, including using acetals, ethers, and silyl ethers. It provides examples of specific protecting groups like THP, MEM, benzyl ethers, and trialkylsilyl ethers.
This document summarizes the principles and applications of Mossbauer spectroscopy, also known as nuclear gamma resonance spectroscopy. It discusses how Mossbauer spectroscopy probes nuclei using gamma rays and measures gamma absorption spectra. It explains how nuclei in solid crystals can undergo nuclear resonance because they are bound and not free to recoil. The document also outlines several key parameters that must be satisfied for Mossbauer spectroscopy to be effective, including the energy of nuclear transitions and lifetimes of excited states. Finally, it provides examples of how Mossbauer spectroscopy has been used to identify iron oxide nanoparticles in magnetotactic bacteria.
This document discusses proton magnetic resonance spectroscopy (NMR spectroscopy), specifically focusing on spin-spin coupling, coupling constants, and the different types of coupling that can occur including geminal, vicinal, and long range coupling. It explains that the coupling constant value increases with increasing bond angle and electronegativity. It also discusses first order spectra and provides examples of geminal, vicinal, and long range coupling, as well as factors that affect coupling constant values.
Photochemistry is the branch of chemistry concerned with chemical reactions caused by light absorption. Photochemical reactions proceed differently than thermal reactions and can form thermodynamically disfavored products or overcome large activation barriers. When a molecule absorbs light, it is elevated to an excited state. The Grotthuss–Draper law states that light must be absorbed for a photochemical reaction to occur. Absorbed light can excite a molecule to different singlet or triplet states, which can then relax through radiationless or radiative processes like fluorescence or phosphorescence. Experimental factors like light sources, reactors, solvents, and wavelength selection influence photochemical reactions.
This document discusses double resonance in nuclear magnetic resonance (NMR) spectroscopy. It explains spin decoupling techniques that are used to simplify complex NMR spectra. By irradiating coupled protons, decoupling can eliminate splitting of signals and cause multiplets to collapse into doublets or singlets. This produces easier to interpret spectra. Decoupling is demonstrated on an ethanol sample, where exchanging hydrogens for deuterium causes signals to disappear. Irradiating methyl hydrogens in a molecule can also simplify signals by removing coupling to adjacent protons. Decoupling enhances spectral signals and allows clearer distinction between them.
This document provides an overview of Fourier transform infrared (FT-IR) spectroscopy. It discusses the electromagnetic spectrum and how infrared radiation lies between visible light and microwaves. Infrared spectroscopy works by detecting the vibrations of bonds between atoms in molecules as they absorb infrared light. An FT-IR uses an interferometer to measure an infrared spectrum with advantages of high sensitivity, accuracy, and resolution compared to other methods. The document outlines applications of infrared spectroscopy such as pharmaceutical analysis and environmental monitoring.
The document introduces the Heck reaction, which is a coupling reaction where a metal catalyst aids in coupling two hydrocarbon fragments. Specifically, the Heck reaction involves converting a terminal alkene to an internal alkene. Richard Heck, Ei-ichi Negishi, and Akira Suzuki were jointly awarded the Nobel Prize in 2010 for their work developing palladium-catalyzed C-C cross coupling reactions, including the Heck reaction. The mechanism of the Heck reaction involves oxidative addition, insertion, β-H elimination, and reductive elimination steps.
The document discusses nuclear magnetic resonance (NMR) spectroscopy, specifically proton (1H) and carbon-13 (13C) NMR. It provides information on why NMR is used, the types of information it can provide about compounds, and the physical properties of 1H and 13C nuclei that influence their NMR spectra. It also discusses factors that affect chemical shifts, common chemical shift ranges, coupling behaviors, and how to determine the number of signals expected for given compounds from their carbon environments. The document aims to explain the fundamentals and applications of 1H and 13C NMR spectroscopy.
Mossbauer spectroscopy involves the resonant absorption of gamma rays by atomic nuclei. It was first observed by Mossbauer in 1958, for which he received the Nobel Prize. The basic principles are that nuclei emitting gamma rays lose a small amount of energy to recoil, while absorbing nuclei must have slightly higher energy for resonance to occur. Doppler shift is used to scan the gamma ray energy through a range and bring the source and sample nuclei into resonance by accelerating the source. The technique provides information about oxidation states, spin states, and local environments of atoms in samples.
The document summarizes the Tiffeneau–Demjanov rearrangement reaction. It was discovered in the early 1900s by French chemist Marc Émile Pierre Adolphe Tiffeneau and Russian chemist Nikolay Yakovlevich Demyanov. The reaction involves treating 1-aminomethyl-cycloalkanol with nitrous acid to form an enlarged cycloketone through a 1,2-carbon migration. This ring expansion reaction is useful for increasing the size of amino-substituted cyclic compounds from four to eight-membered rings. The mechanism involves diazotization of the amine to form a diazonium ion that undergoes 1,2-alkyl shift accompanied by nitrogen loss to form
This document provides an overview of stereochemistry. It discusses the history of stereochemistry beginning with Pasteur's discovery of optical isomerism in tartaric acid in 1849. Van't Hoff and LeBel later explained optical activity in terms of tetrahedral carbon atom arrangements. The document defines types of stereoisomers including enantiomers, which are non-superimposable mirror images, and diastereomers. It also discusses concepts like chirality, optical activity, and racemic mixtures. Baeyer strain theory is explained as it relates to stability and reactivity of cycloalkanes based on bond angle deviations from ideal values. Conformational analysis of ethane and cyclohexane are also summarized.
This document discusses different types of isomerism in organic chemistry, including structural isomerism, stereoisomerism, and optical isomerism. It defines isomerism as compounds with the same molecular formula but different properties. The main types of structural isomerism are chain, position, functional, metamerism, and tautomerism. Stereoisomerism includes conformational and configurational isomers, with the latter including optical isomers and geometric isomers. Optical activity and how it relates to chirality and asymmetric carbons is also explained. Different projection formulas used to depict three-dimensional chiral molecules in two dimensions are also presented.
This document discusses the properties of solid state materials. It defines crystalline and amorphous solids, and describes the different types of crystal structures including simple cubic, body-centered cubic, and face-centered cubic. It also discusses crystal symmetry, unit cells, Bravais lattices, coordination number, X-ray crystallography, Bragg's law, and the different classifications of crystals based on bonding.
The document discusses the topic of stereochemistry. It defines stereoisomers as isomers that have the same molecular formula and structural formula but differ in the spatial arrangement of atoms. There are two main types of stereoisomers - configurational isomers and conformational isomers. Configurational isomers cannot be interconverted without breaking chemical bonds, while conformational isomers can rapidly interconvert. Specific examples of configurational isomers discussed are enantiomers, which are non-superimposable mirror images, and geometric isomers, which differ in geometry about a double bond. Methods for separating enantiomers like formation of diastereomeric salts are also summarized.
The document provides an introduction to stereochemistry, which is the study of three-dimensional arrangements of atoms in molecules. It discusses how stereoisomers can have the same molecular formula but different spatial arrangements. The importance of stereochemistry is highlighted using the examples of starch and cellulose, which are stereoisomers that have different properties. The document also summarizes the thalidomide disaster which demonstrated the significance of stereochemistry due to different biological effects of stereoisomers. Key concepts like chiral carbon, enantiomers, diastereomers, and optical activity are defined.
The document discusses chiral molecules and enantiomers. It explains that chiral molecules are nonsuperimposable on their mirror images and thus have "handedness." Enantiomers are a type of stereoisomer that are mirror images of each other. The document uses 2-butanol as an example to illustrate that molecules containing a tetrahedral carbon with four different groups attached can exist as a pair of enantiomers. Interchanging any two groups at this stereocenter results in the other enantiomer. Enantiomers do not spontaneously interconvert as it requires breaking chemical bonds.
1. Stereoisomers differ in how atoms or groups of atoms are oriented in space, even if they have the same molecular formula and bonding. There are two types: conformational isomers, which rapidly interconvert, and configurational isomers, which do not.
2. Enantiomers are non-superimposable mirror images of each other and are examples of configurational isomers. A mixture of equal parts of both enantiomers is called a racemic mixture.
3. Chiral molecules have asymmetric carbon atoms bonded to four different groups and can exist as enantiomers. Common methods to represent chiral molecules include wedge diagrams, Fischer projections, and Newman projections.
Best PowerPoint presentation on NCERT class 9 Atoms and Molecules as per CBSE syllabus it covers full chapter with all information.
By Raxit Gupta
9C
KENDRIYA VIDYALAYA BALLYGUNGE
The document discusses several key concepts in chemistry including:
- Laws of chemical combination and conservation of matter discovered by scientists like Lavoisier and Proust through quantitative experiments.
- Proust's law of constant proportions which states that elements are always present in a definite proportion by weight in a compound.
- Atoms being the fundamental units of matter and their structure including subatomic particles. Atoms are extremely small but their masses can be measured by comparison to hydrogen atoms.
- Chemical symbols used to represent elements, including early systems and current IUPAC symbols. Molecules can be monoatomic or polyatomic.
- Concepts of mole, molar mass, and Avogadro
This document provides an overview of stereochemistry and stereoisomers. It begins by defining stereochemistry and noting that it refers to the three-dimensional arrangement of atoms in a molecule. It then discusses Louis Pasteur's 1848 discovery of chirality and enantiomers through his experiments with tartaric acid crystals. The document defines key terms like chiral, achiral, enantiomers, and diastereomers. It explains the different types of stereoisomers including those arising from chiral centers and geometric isomers like cis-trans. The document emphasizes that stereoisomers can have different physical and chemical properties despite having the same molecular formula.
This document provides an overview of atomic theory and the laws of chemical combination. It discusses the early Greek philosophers' debates on the nature of matter and whether it is continuous or made of discrete particles. John Dalton developed the modern atomic theory in the early 19th century, which included five main points. The document outlines the contributions of scientists like Thomson, Rutherford, and Bohr to models of atomic structure. It describes the three states of matter and defines the fundamental laws of conservation of mass, definite proportions, and multiple proportions discovered by scientists like Lavoisier, Proust, and Dalton. Examples are provided to illustrate applications of these laws.
This document discusses stereochemistry and isomerism. It defines constitutional and stereoisomers, and describes different types of constitutional isomers like chain, position, functional, and tautomeric isomers. It also discusses configurational isomerism including optical isomers like enantiomers and diastereomers. Chirality and chiral centers are explained. Methods to represent 3D structures in 2D like Fischer projections are introduced. The document also covers topics like optical activity, polarimetry and racemic mixtures.
The document discusses several nuclear fusion reactions that occur in stars, including the proton-proton chain reaction, alpha process, CNO cycle, and triple-alpha process. The proton-proton chain reaction fuses hydrogen into helium. The alpha process fuses helium into heavier elements. The CNO cycle is another reaction that fuses hydrogen into helium using carbon, nitrogen, and oxygen as catalysts. The triple-alpha process fuses three helium nuclei into carbon.
Atomic Structure, Sub atomic particles named as electrons, protons and neutronsNaveedAhmad717735
Atom is composed of Sub atomic particles named as electrons, protons and neutrons. For further details https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_A_Molecular_Approach_(Tro)/02%3A_Atoms_and_Elements/2.04%3A_The_Discovery_of_the_Electron
LESSON 2 THE DEVELOPMENT OF THE ATOMIC THEORY.pptxMaryAnnFrias3
1. The document traces the development of atomic theory from ancient Greek philosophers Democritus and Aristotle to modern scientists like Dalton, Thomson, Rutherford, and Bohr.
2. Rutherford's gold foil experiment disproved Thomson's plum pudding model of the atom and led him to propose the nuclear model with electrons orbiting a small, dense nucleus.
3. The discovery of the proton, neutron, and Bohr's model of electron orbits further refined scientific understanding of atomic structure.
This document discusses the development of atomic theory from ancient Greece to modern times. It begins with Democritus' idea in 400 BC that matter is made of indivisible atoms. John Dalton expanded on this in 1803 with his Billiard Ball Model, proposing atoms as tiny invisible particles that make up elements. Ernest Rutherford discovered the nucleus in 1911 and protons in 1920 with his Planetary Model. Niels Bohr proposed fixed electron energy levels around the nucleus in 1913. Modern atomic theory incorporates Erwin Schrodinger's 1926 Electron Cloud Model and James Chadwick's 1932 discovery of neutrons in the nucleus.
This document discusses Dalton's atomic theory from the early 1800s. It introduces some key ideas:
1) Dalton proposed that matter is made of indivisible atoms and that atoms of different elements have different masses.
2) His theory explained laws of conservation of mass and constant proportions from chemical experiments.
3) It introduced ideas that in compounds, elements combine in small whole number ratios and that during chemical reactions atoms are rearranged but not destroyed.
1) John Dalton proposed the first atomic theory in 1803 which described atoms as indivisible particles and that elements are made of unique atoms that combine in whole number ratios.
2) In the early 1900s, experiments revealed atoms have subatomic particles including electrons, protons, and neutrons. Protons and neutrons are in the tiny nucleus while electrons surround it.
3) The number of protons determines an element's identity. Atoms are neutral due to equal numbers of protons and electrons.
Structure of matter atoms and moleculesSuman Tiwari
- An atom is the smallest particle of an element that retains the chemical properties of that element. All atoms of the same element are identical.
- Atoms are very small, not visible even under a powerful microscope. Models like the ball-and-stick model are used to represent atoms and molecules.
- Atoms consist of even smaller subatomic particles - protons, neutrons, and electrons. Protons and neutrons are located in the nucleus, while electrons orbit the nucleus. The number of protons determines the element.
Similar to PPT-1P-Stereochemistry-Part-1-1.pdf (20)
This document announces the winners of the 2024 Youth Poster Contest organized by MATFORCE. It lists the grand prize and age category winners for grades K-6, 7-12, and individual age groups from 5 years old to 18 years old.
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3. Scope
• Stereochemistry (from the Greek stereos, meaning solid) refers to
chemistry in space i.e., in three dimensions and describes chemistry
as a function of molecular geometry. Since most molecules are
three-dimensional (3D), stereochemistry, in fact, pervades all of
chemistry.
• Stereochemistry can be factorised into its static and dynamic
aspects. Static stereochemistry (stereochemistry of molecules) deals
with the counting of stereoisomers (isomeric compounds of
identical structure but differing in the arrangement of the atoms in
three-dimensional space), with their structure (i.e., molecular
architecture), with their energy, and with their physical and most of
their spectral properties.
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
4. Scope
• Dynamic stereochemistry (or stereochemistry of reactions) deals
with the stereochemical requirements and the stereochemical
outcome of chemical reactions, including interconversion of
conformational isomers or topomers; this topic is deeply interwoven
with the study and understanding of reaction mechanisms.
• Today, the scope of stereochemistry extends considerably beyond
the static description of molecular geometry and of the physical
properties related to such geometry; stereochemistry is concerned
also with the relationships in space between the different atoms and
groups in a molecule during chemical reactions and the way in
which chemical equilibria and rates of reaction are affected by those
spatial relationships.
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
5. History
• The origins of sterochemistry stem from the discovery of plane-
polarized light by the French physicist Malus (1809). In 1812
another French scientist, Biot discovered that a quartz plate, cut at
right angles to its crystal axis, rotates the plane of polarized light
through an angle proportional to the thickness of the plate; this
constitutes the phenomenon of optical rotation.
• Some quartz crystals turn the plane of polarisation to the right,
while others turn it to the left. Biot (1815) extended these
observations to organic substances-both liquids (such as
turpentine) and solutions of solids (such as sucrose, camphor, and
tartaric acid). Biot recognized the difference between the rotation
produced by quartz and that produced by the organic substances he
studied.
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
6. History
• According to Biot, the rotation produced by quartz is a property of
the crystal. It is observed only in the solid state and depends on the
direction in which the crystal is viewed, whereas the latter (rotation
produced by the organic substances) is a property of the individual
molecules, and may, therefore, be observed not only in the solid,
but in the liquid and gaseous states, as well as in solution.
• With respect to the question of the cause of optical rotation, the
French mineralogist Hauy had already noticed in 1801 that quartz
crystals exhibit the phenomenon of hemihedrism. Hemihedrism
may be defined as the absence of a plane, centre, or altenating axis
of symmetry in the crystal. In crystals presenting hemihedrism,
there are faces that make such crystals non-superposable with their
mirror images. Such mirror-image crystals are called
“enantiomorphous,” from the Greek enantios meaning opposite
and morphe form.
7. History
• In 1822, Sir John Herschel, a British astronomer, observed that
there was a relation between hemihedrism and optical rotation. All
the quartz crystals having the odd faces inclined in one direction
rotate the plane of polarized light in one and the same sense,
whereas the enantiomorphous crystals rotate polarized light in the
opposite sense.
• Louis Pasteur extended this correlation from the realm of crystals,
such as quartz, which rotate polarized light only in the solid state,
to the realm of molecules, such as dextro-tartaric acid, which rotate
both as the solid and in solution. [dextro-Tartaric acid, henceforth
denoted as (+)-tartaric acid, rotates the plane of polarized light to
the right.
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
8. History
• In 1848 Pasteur had succeeded in separating crystals of the sodium
ammonium salts of (+)- and (-)-tartaric acid from the racemic
(nonrotating) mixture. When the salt of the mixed (racemic) acid,
which is found in wine caskets, was crystallized by slow
evaporation of its aqueous solution, large crystals formed which
displayed hemihedric crystals similar to those found in quartz.
• By looking at these crystals with a lens, Pasteur was able to separate
the two types (with their dissymmetric facets inclined to the right or
left) by means of a pair of tweezers. When he then separately
redissolved the two kinds of crystals, he found that one solution
rotated polarized light to the right [the crystals being identical with
those of the salt of the natural (+)-acid], whereas the other rotated to
the left. [(-)-Tartaric acid had never been encountered up to that
time.]
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
9. History
• Pasteur (1860) soon came to realize the analogy between crystals
and molecules. In both cases the power to rotate polarized light was
caused by dissymmetry, that is the non-identity of the crystal or
molecule with its mirror image, expressed in the case of the
ammonium sodium tartrate crystal by the presence of the
hemihedric faces.
• Similarly, Pasteur postulated, the molecular structures of (+)- and
(-)-tartaric acids must be related as an object to its mirror image.
The two acids are thus enantiomorphous at the molecular level.
They are called as enantiomers. [The ending -mer (as in isomer,
polymer, etc., come from the Greek meros meaning part) usually
refers to a molecular species.]
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
10. History
• In 1874, van't Hoff (1874, 1875) and Le Be1 (1874) independently
and almost simultaneously proposed the case for enantiomerism in a
substance of the type Cabcd: the four substituents are arranged
tetrahedrally around the central carbon atom to which they are
linked.
• The four linkages to a carbon atom point
toward the corners of a regular
tetrahedron (Figure 1) and two
nonsuperposable arrangements of atoms
or groups (enantiomers) are thus
possible.
• The model corresponding to a given enantiomer (e.g., Figure 1; A)
and the molecule that it represents are called “chiral” (meaning
handed, from Greek cheir, hand) because, like hands, the molecules
are not superposable with their mirror images.
11. Chiral Molecules and Chiral Samples
• When a molecule is chiral, it must be either “right-handed” or “left-
handed”. But if a substance or sample is said to be chiral, this
merely means that it is made up of chiral molecules; it does not
necessarily imply that all the constituent molecules have the same
“sense of chirality”.
• The statement that a macroscopic sample (as distinct from an
individual molecule) is chiral is ambiguous. It may be racemic or
non-racemic.
• Chiral and non-racemic sample: The sample is made up of
molecules that all have the same sense of chirality (homochiral
molecules).
• Chiral but racemic sample: The sample is made up of equal (or
very nearly equal) numbers of molecules of opposite sense of
chirality (heterochiral molecules).
12. Chiral Molecules and Chiral samples
• There is, however, little ambiguity about the meaning of “chiral,
racemic”: Chiral, racemic means that the sample is made up of
equal numbers of molecules of opposite sense of chirality. But in a
“chiral, non-racemic” sample there can be some molecules of a
sense of chirality opposite to that of the majority; that is, the sample
may not be enantiomerically pure (or enantiopure).
• Everything has a mirror image. What’s important in chemistry is
whether a molecule is identical to or different from its mirror image.
Some molecules are like hands. Left and right hands are mirror
images of each other, but they are not identical (Figure 2). If one
hand is placed on the other, they can never superimpose either all
the fingers, or the tops and palms. Socks, on the contrary, are
superposable to each other (Figure 2).
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
13. Chiral and Achiral Molecules
• To superimpose an object on its mirror image means to align all
parts of the object with its mirror image. With molecules, this
means aligning all atoms and all bonds.
• A molecule (or object) that is not superimposable on its mirror
image is said to be chiral.
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
14. Chiral and Achiral Molecules
• Other molecules are like socks. Two socks from a pair are mirror
images that are superimposable. One sock can fit inside another. A
sock and its mirror image are identical.
• A molecule (or object) that is superimposable on its mirror image is
said to be achiral.
Answer the Following Questions
1. There are twenty-six letters in English language. How many of
them are symmetric and how many of them are non-symmetric,
considering them as two-dimensional.
2. Classify the following as chiral or achiral. Give reasons.
(a) H2O (ii) CH2BrCl (iii) CHBrClF
15. Ordinary Light and Plane Polarised Light
• An ordinary light beam consists of a group of electromagnetic
waves of a range of different wavelengths that vibrate in many
different planes at right angles to the direction of propagation of the
light ray. It vibrates in all directions as in Figure 4A.
• When such a beam strikes a polarising film or a Nicol prism (made
from a crystal of calcium carbonate) only those waves vibrating in a
specific plane with respect to the axis of the film or prism may pass
through; all others are blocked out. Upon emergence the light beam
is plane polarised as in Figure 4B. Here, all of its waves vibrate in a
single plane (or, more precisely, in parallel planes). Light of this
kind is said to be polarised. French physicist Malus discovered this
light in 1809.
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
16. Ordinary Light and Plane Polarised Light
• Monochromatic light: Monochromatic light, such as emitted by a
sodium lamp (λ = 589 nm), is of discrete wavelength but still
vibrates in an infinite number of planes.
• The term monochromatic derives from the Greek words monos,
meaning one or sole, and chromos, meaning color.
17. Isomers
• In organic chemistry, isomers are molecules with the same
molecular formula (i.e. the same number of atoms of each element),
but different structural or spatial arrangements of the atoms within
the molecule. Therefore, isomers are the different compounds with
the same molecular formula.
• On the basis of bonding connectivity (The term connectivity, or
bonding sequence, describes the way atoms are connected together,
or their bonding relationships to one another, in covalent
compounds. For example, in the methane molecule one carbon is
connected to four hydrogen atoms simultaneously, while each
hydrogen atom is connected to only one carbon.), isomers are
divided into two major classes: constitutional or structural isomers
and stereoisomers.
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
18. Constitutional or Structural Isomers
• Constitutional or structural isomers are compounds with the same
molecular formula but different structural formulae. In isomerism,
constitutional isomers are molecules of different connectivity.
Therefore, constitutional isomers differ in the way the atoms are
connected to each other.
• Constitutional isomers have:
1. different IUPAC names
2. different bonding connectivity
3. the same or different functional groups
4. different physical properties, so they are separable by physical
techniques such as distillation.
5. different chemical properties. They behave differently or give
different products in chemical reactions.
19. Constitutional or Structural Isomers
• Structural isomers can be split again into three main subgroups:
chain isomers, position isomers, and functional group isomers.
• Chain isomers are molecules with the same molecular formula, but
different arrangements of the carbon ‘skeleton’. Organic molecules
are based on chains of carbon atoms, and for many molecules this
chain can be arranged differently (Figure 5): either as one,
continuous chain, or as a chain with multiple side groups of carbons
branching off.
• For example, there are two isomers of
butane, C4H10. In one of them (A), the
carbon atoms lie in a “straight chain”
whereas in the other (B) the chain is
branched.
20. Constitutional or Structural Isomers
• Positional isomers are constitutional
isomers that have the same carbon
skeleton and the same functional
groups but differ from each other in
the location of the functional groups
on or in the carbon chain (Figure 6).
• Functional isomerism occurs when
substances have the same molecular
formula but different functional groups.
This means that functional isomers belong
to different homologous series. They can
be alcohols and ethers; aldehydes and
ketones; carboxylic acids and esters, etc.
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
21. Stereoisomers
• In stereochemistry, stereoisomerism, or spatial isomerism, is a form
of isomerism in which molecules have the same molecular formula
and sequence of bonded atoms (bonding connectivity), but differ in
the three-dimensional orientations of their atoms in space. This
contrasts with structural isomers, which share the same molecular
formula, but the bond connections or their order differs.
• Stereoisomers have identical IUPAC names (except for a prefix like
cis or trans). Because they differ only in the three-dimensional
arrangement of atoms, stereoisomers always have the same
functional group(s).
• There are two main types of stereoisomerism-geometric isomerism,
and optical isomerism.
22. Geometrical Isomers
• Stereoisomerism ascribed to different directional arrangements of
specifically located groups in the molecule and usually considered
to be caused by prevention of free rotation in parts of the molecule
(as by a double bond or a ring).
• This type of isomerism most frequently involves in compounds
containing carbon-carbon double bonds with suitable substituents.
Rotation of these bonds is restricted, compared to single bonds,
which can rotate freely.
• This means that, if there are two different
atoms, or groups of atoms, attached to each
carbon of the carbon carbon double bond,
they can be arranged in different ways to
give different molecules (Figure 8).
This Lecture is prepared by Dr. K. K. Mandal, SPCMC, Kolkata
23. Optical Isomers
• Optical isomers are two compounds which contain the same
number and kinds of atoms, and bonds (i.e., the connectivity
between atoms is the same), and different spatial arrangements of
the atoms, but which have non-superimposable mirror images. Each
non-superimposable mirror image structure is called an enantiomer.
• Optical isomers are so named due to their effect on plane-polarised
light, and come in pairs. They usually (although not always) contain
a chiral centre – this is a carbon atom, with four different atoms (or
groups of atoms) attached to it.
• These atoms or groups can be arranged
differently around the central carbon, in
such a way that the molecule can’t be
rotated to make the two arrangements
align (Figure 9).
25. The Importance of Isomerism
• Isomers of the same molecule have the potential to have different physical or
chemical properties. These differences can have some important implications.
• Thalidomide (Figure 10), a drug was prescribed in the 1950s and 60s to treat
morning sickness in pregnant women; however, unknown then was that the
(S)-enantiomer could be transformed in the body into compounds that caused
deformities in embryos. The two enantiomers also interconvert in the body,
meaning that even if just the (R)-enantiomer could be isolated, it would still
produce the same effects.
• This emphasised the importance of testing all of the optical isomers of drugs for
effects, and is part of the reason why present-day pharmaceuticals have to go
through years of rigorous tests, to ensure that they are safe.