Stereochemistry Stereo Chemistry

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SHRI VISHNU ENGINEERING COLLEGE FOR WOMEN::BHIMAVRAM (AUTONOMOUS) DEPARTMENT OF BASIC SCIENCE APPLIED CHEMISTRY/ENGINEERING CHEMISTRY UNIT-6 HAND OUT ON STEREOCHEMISTRY STEREO CHEMISTRY ISOMERS & ISOMERISM Compounds posses same molecular formula but differ from each other in physical or chemical properties and are called isomers and the phenomenon is called isomerism. ISOs = equal Meros = parts When isomerism is due to the difference in the arrangement of atoms within the molecule, without any reference to space, the phenomenon is referred to as “Structural Isomerism”. Structural Isomerism is of five types: 1. Chain Isomers. 2. Position Isomers. 3. Functional Isomers. 4. Metamerism. 5. Tautomerism. Chain Isomerism Isomers are chain isomers when two or more compounds have the same molecular formula but differ in the branching of carbon atoms. For example, we can represent C5H12 as three compounds: CH3CH2CH2CH2CH3– pentane Guess the remaining two structure possible by C5H12 Position Isomerism Isomers are position isomers when the two or more compounds differ in the position of the functional group or substituent atoms. For example, we can represent C3H7OH in two arrangements: CH3CH2CH2OH -Propan-1-ol CH3CHOHCH3 -Propan-2-ol Functional Isomerism Isomers are functional isomers when the two or more compounds have an identical molecular formula but differ in the functional group present. These isomers are the functional isomers. For example, we can represent C3H6O as a ketone and as an aldehyde. Aldehyde Ketone v) Tautomerism Stereo Isomerism Stereoisomerism is a phenomenon in which compounds have the same molecular formula but differ in the relative positioning or orientation of atoms in space. Stereoisomers are the compounds exhibiting stereoisomerism. We can further classify stereoisomerism into: Geometric Isomerism: it is shown by molecules in which their spatial positions are locked to each other due to the presence of a ring structure or a double bond. Optical Isomerism: Two or more compounds which have the same molecular arrangement but differ in the optical activity are optical isomers. Conformational isomerism Optical isomerism Types of Symmetry A meso compound or meso isomer is a stereoisomer with an identical or superposable mirror image i.e., a non-optically active member of a set of stereoisomers, at least two of which are optically active. This means that despite containing two or more stereogenic centers, the molecule is not chiral Plane of symmetry A plane of symmetry is an imaginary plane that bisects a molecule into halves that are mirror images to each other. A symmetry plane can also be identified by its Cartesian orientation, e.g., (xz) or (yz). Center of symmetry or inversion center, abbreviated i. A molecule has a center of symmetry when, for any atom in the molecule, an identical atom exists diametrically opposite this center an equal distance from it..

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A Practical Approach to Chiral Separations by Liquid Chromatography
A Practical Approach to Chiral Separations by Liquid Chromatography Edited by G. Subramanian Weinheim • New York VCH Basel • Cambridge • Tokyo Contents 1 An Introduction to Enantioseparation by Liquid Chromatography Charles A. White and Ganapathy Subramanian 1.1 Introduction 1 1.1.1 What is Chirality? 1 1.1.2 What Causes Chirality? 2 1.1.3 Why is Chirality Important? 4 1.2 Industries which Require Enantioseparations 4 1.2.1 Pharmaceutical Industry 4 1.2.2 Agrochemical Industry 5 1.2.3 Food and Drink Industry 6 1.2.4 Petrochemical Industry 6 1.3 Chiral Liquid Chromatography 7 1.3.1 Type I Chiral Phases 8 1.3.2 Type II Chiral Stationary Phases 10 1.3.3 Type III Chiral Stationary Phases 10 1.3.3.1 Microcrystalline Cellulose Triacetate and Tribenzoate 10 1.3.3.2 Cyclodextrins 11 1.3.3.3 Crown Ethers 11 1.3.3.4 Synthetic Polymers •. 12 1.3.4 Type IV Chiral Stationary Phases 13 1.3.5 Type V Chiral Stationary Phases 13 1.3.6 Mobile Phase Additives 14 1.3.6.1 Metal Complexes 14 1.3.6.2 Ion-pair Formation 15 1.3.6.3 Uncharged Chiral Additives 15 1.4 The Future 16 2 Modeling Enantiodifferentiation in Chiral Chromatography Kenny B. Lipkowitz 2.1 Introduction 19 2.2 Modeling 19 # VIII Contents 2.3 Computational Tools 22 2.3.1 Quantum Mechanics 22 2.3.2 Molecular Mechanics 23 2.3.3 Molecular Dynamics 24 2.3.4 Monte Carlo Simulations 24 2.3.5 Graphics 25 2.4 Modeling Enantioselective Binding in Chromatography 26 2.4.1 Type I CSPs 26* 2.4.2 Type II CSPs 41 2.4.3 Type III CSPs 44 2.5 Related Studies 49 2.6 Summary 50 3 Regulatory Implications and Chiral Separations Jeffrey R.
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A Reminder… Chirality: a Type of Stereoisomerism
A Reminder… Same molecular formula, isomers but not identical. constitutional isomers stereoisomers Different in the way their Same connectivity, but different atoms are connected. spatial arrangement. and trans-2-butene cis-2-butene are stereoisomers. Chirality: A Type of Stereoisomerism Any object that cannot be superimposed on its mirror image is chiral. Any object that can be superimposed on its mirror image is achiral. Chirality: A Type of Stereoisomerism Molecules can also be chiral or achiral. How do we know which? Example #1: Is this molecule chiral? 1. If a molecule can be superimposed on its mirror image, it is achiral. achiral. Mirror Plane of Symmetry = Achiral Example #1: Is this molecule chiral? 2. If you can find a mirror plane of symmetry in the molecule, in any achiral. conformation, it is achiral. Can subject unstable conformations to this test. ≡ achiral. Finding Chirality in Molecules Example #2: Is this molecule chiral? 1. If a molecule cannot be superimposed on its mirror image, it is chiral. chiral. The mirror image of a chiral molecule is called its enantiomer. Finding Chirality in Molecules Example #2: Is this molecule chiral? 2. If you cannot find a mirror plane of symmetry in the molecule, in any conformation, it is chiral. chiral. (Or maybe you haven’t looked hard enough.) Pharmacology of Enantiomers (+)-esomeprazole (-)-esomeprazole proton pump inhibitor inactive Prilosec: Mixture of both enantiomers. Patent to AstraZeneca expired 2002. Nexium: (+) enantiomer only. Process patent coverage to 2007. More examples at http://z.umn.edu/2301drugs. (+)-ibuprofen (-)-ibuprofen (+)-carvone (-)-carvone analgesic inactive (but is converted to spearmint oil caraway oil + enantiomer by an enzyme) Each enantiomer is recognized Advil (Wyeth) is a mixture of both enantiomers.
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Pyrethroid Stereoisomerism: Diastereomeric and Enantiomeric Selectivity in Environmental Matrices – a Review
Orbital: The Electronic Journal of Chemistry journal homepage: www.orbital.ufms.br e-ISSN 1984-6428 | Vol 10 | | No. 4 | | Special Issue June 2018 | REVIEW Pyrethroid Stereoisomerism: Diastereomeric and Enantiomeric Selectivity in Environmental Matrices – A Review Cláudio Ernesto Taveira Parente*, Claudio Eduardo Azevedo-Silva, Rodrigo Ornellas Meire, and Olaf Malm Laboratório de Radioisótopos, Instituto de Biofísica, Universidade Federal do Rio de Janeiro. Av. Carlos Chagas Filho s/n, bloco G, sala 60, subsolo - 21941-902. Cidade Universitária, Rio de Janeiro, RJ. Brasil. Article history: Received: 30 July 2017; revised: 10 October 2017; accepted: 08 March 2018. Available online: 11 March 2018. DOI: http://dx.doi.org/10.17807/orbital.v10i4.1057 Abstract: Pyrethroids are chiral insecticides characterized by stereoisomerism, which occurs due to the presence of one to three asymmetric (chiral) carbons, generating one or two pairs of cis/trans diastereomers, and two or four pairs of enantiomers. Diastereomers have equal chemical properties and different physical properties, while enantiomer pairs, have the same physicochemical properties, with exception by the ability to deviate the plane of polarized light to the right or to the left. However, stereoisomers exhibit different toxicities at the metabolic level, presenting enzyme and receptor selectivity in biological systems. Studies in aquatic organisms have shown that toxic effects are caused by specific enantiomers (1R-cis and 1R-trans) and that those cause potential estrogenic effects (1S-cis and 1S- trans). In this context, the same compound can have wide-ranging effects in organisms. Therefore, several studies have highlighted pyrethroid stereochemical selectivity in different environmental matrices. The analytical ability to distinguish the diastereomeric and enantiomeric patterns of these compounds is fundamental for understanding the processes of biotransformation, degradation environmental behavior and ecotoxicological impacts.
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Chapter 5: Stereoisomerism [Sections: 5.1-5.9]
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University of Warwick Institutional Repository
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Application of Chiral Sulfoxides in Asymmetric Synthesis
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A Review on Chiral Chromatography and Its Application to the Pharmaceutical Industry
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Nonlinear Effects in Enantioselective Organometallic Catalysis H
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1 the Historical Development of Asymmetric Hydrogenation
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