DOCSLIB.ORG

1515564961CHE P1 M23 Etext.Pdf

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
1515564961CHE P1 M23 Etext.Pdf ____________________________________________________________________________________________________ Subject Chemistry Paper No and Title 1: Organic Chemistry I (Nature of Bonding & Stereochemistry) Module No and Title 23: Enantiotopic & Diastereotopic atoms , groups and faces Module Tag CHE_P1_M23 TABLE OF CONTENTS 1. Learning Outcomes 2. Introduction 3. Topicity and Prostereoisomerism 4. Homotopic ligand and faces 4.1. Substitution-addition criterion 4.2. Symmetry criterion 5. Stereoheterotopic ligands and faces 5.1. Enantiotopic ligands and faces CHEMISTRY PAPER 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) MODULE 23: Enantiotopic and diastereotopic atoms, groups and faces ____________________________________________________________________________________________________ 5.1.1. Substitution-addition criterion 5.1.2. Symmetry criterion 5.2. Diastereotopic ligands and faces 5.2.1. Substitution-addition criterion 5.2.2. Symmetry criteron 6. Nomenclature 6.1. Symbols for Stereoheterotopic ligands 6.1.1. Molecule with single prochiral centre 6.1.2. Molecules with pre-pseudoasymmetric centre 6.1.3. Molecules with prochiral axis 6.1.4. Molecules with prochiral plane 6.2. Symbols for Stereoheterotopic faces 6.2.1. Enantiotopic faces 6.2.2. Diastereotopic faces 7. Summary CHEMISTRY PAPER 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) MODULE 23: Enantiotopic and diastereotopic atoms, groups and faces ____________________________________________________________________________________________________ 1. Learning Outcomes Learn what are homotopic and heterotopic ligands. Understand about the “Topicity” and “Prostereoisomerism” Study about homotopic ligands and faces by using substitution-addition and symmetric criteria. Know about enantiotopic ligands and faces by using substitution-addition and symmetric criteria. Know about diastereotopic ligands and faces by using substitution-addition and symmetric criteria. Learn the nomenclature of stereoheterotopic ligands and faces. 2. Introduction As we know, when the atoms or group of atoms in the molecule are superimposable then they are homomorphic. These homomorphic atoms or groups can be distinguished if they are bonded to constitutionally different centres or if they have different spacial relation to the rest of the molecule. This can be clearly understood by taking an example of n- pentane (Figure 1.). Figure 1. Homotopic and Heterotopic atoms CHEMISTRY PAPER 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) MODULE 23: Enantiotopic and diastereotopic atoms, groups and faces ____________________________________________________________________________________________________ In this case the H-atoms at C-2 are constitutionally heterotopic (‘topos’ means ‘place’ in Greek). These C-2 H’s are stereoheterotopic as their spacial relation is different with the rest of the molecule. In this molecule, the plane Me-C-Pr divides it into two halves, the right and the left which are stereochemically distinguishable (enantiomorphic in present case), actually making two H’s stereochemically non equivalent i.e., stereoheterotopic. These H’s can be recognized hypotheically by replacing them with other atoms say Br in this case, this results in two enantiomers as shown in the Figure 1. Similarly, if the replacement is by constitutionally heterotopic ligands this would results to constitutional isomers e.g., if Me or Pr are replaced by chiral groups then it becomes diastereomorphic with respect to the plane and bromination at the C-2 leads to two diastereomers which also makes the two H’s stereoheterotopic. Whereas the geminal H’s of C-3 cannot distinguish two halves, as it resides in Et-C-Et plane which is two-dimentionally achiral. So, the replacement by Br at C-3 gives the identical products. So, these H’s are considered as homotopic. All these are discussed in more detail in later section of this module. 3. Topicity and Prostereoisomerism In 1967, Mislow and Raban explained the concept of stereoheterotopicity and in 1966 Hanson gave the concept of prochirality which is reviewed by Eliel in 1982. Stereoheterotopicity and prostereoisomerism are related phenomena as the molecules which have stereoheterotopic ligands must exhibits prostereoisomersim (only when the ligands can be reacted on). The term chirality in prostereoisomersim is replaced by the term prochirality. Prochirality is defined as “if two homomorphic ligands at a prochiral centre (or axis or plane) be made different, a chiral center (or axis or plane) would result. In general, a molecule with formula Xaabc represents prochiral centre. As discussed in n- pentane which exhibits prostereoisomersim, with C-2 & C-4 as prostereogenic centres. Like in stereoisomerism we discussed about stereogenic elements such as centres, axes CHEMISTRY PAPER 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) MODULE 23: Enantiotopic and diastereotopic atoms, groups and faces ____________________________________________________________________________________________________ and planes similarly prostereoisomersim is also described in terms of analogous prostereogenic elements, i.e., prostereocentres, prosteroaxes, and prostereoplanes. Also two faces of appropriate molecules may also be stereoheterotopic and reactions on either face would lead to different stereoisomers. Topicity describe the relationship of two or more homomorphic ligands (or faces) which together constitute a set. Hence, a ligand cannot by itself be called homotopic or heterotopic; in order to use this terminology, a comparison with other homomorphic ligand or ligands present either in the same molecule (internal comparison) or in a different molecule (external comparison) is necessary. 4. Homotopic ligands and faces Two criteria, namely, substitution-addition criterion and (or) a symmetry criterion are used to determine the relationships of homomorphic ligands and faces (only one test adequate). 4.1 Substitution-addition criterion Two homomorphic ligands are homotopic if substitution of first one and then the other by an atom or a group which is not already attached to the ligating centre gives identical product. For example, all hydrogen atoms in methylene dichloride methyl chloride, ethylene, and allene (Figure 2.) are homotopic. (Substitution of hydrogen atoms in each set gives a single product) Figure 2. Homotopic ligands CHEMISTRY PAPER 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) MODULE 23: Enantiotopic and diastereotopic atoms, groups and faces ____________________________________________________________________________________________________ The two methine hydrogens in (+), - tartaric acid (I) [as also in the (-)-enantiomer] are also homotopic since their respective replacement by deuterium leads to identical product (Figure 3.). Figure 3. Homotopicity in tartaric acid Two faces of a double bond are homotopic if addition to either face gives identical product, e.g., formation of ethanol by addition of MeMgI to either face of formaldehyde (Figure 4). The two faces of the dialkyl sulphide (IV) are homotopic by the same manner. Alternatively, the two lone pairs may be considered to be homotopic. Figure 4. Homotopic faces 4.2 Symmetry criterion Ligands are homotopic (by internal comparison) if they can interchange positions by rotation around a simple axis Cn ( > n > 1). Thus the two hydrogen in methylene dichloride, the three hydrogens of methyl chloride, and the four hydrogens of ethylene can interchange positions through rotations around C2, C3 and C2 axes respectively (Figure 2). In allene, the geminal hydrogens are interchangeable in pairs by rotation around the molecular axis (C2 axis) while the non-geminal hydrogens are interchangeable CHEMISTRY PAPER 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) MODULE 23: Enantiotopic and diastereotopic atoms, groups and faces ____________________________________________________________________________________________________ through rotation around the two C2 axis perpendicular to the former. All the four hydrogen atoms are thus homotopic. Similarly, for (+)- tartaric acid the two methine protons are interchangeable through rotation around a C2 axis either in the eclipsed conformation or in a staggered conformation. This pairs of ligands are, therefore, homotopic. The following points may be noted: (1) Any achiral or chiral molecule with a Cn axis ( > n >1) must contain at least one set of homotopic. (2) Molecules belonging to non-axial point groups, such as C1, CS and Ci and also Cv do not possess any Cn axis cannot have homotopic ligands. (3) For conformationally mobile systems, if the structural change is rapid on the time scale of observation, homomorphic ligands (interchanged under condition of fast rotation) are homotopic (e.g., H’s in cyclohexane). (4) In a rigid molecule, the number of homotopic ligands belonging to a set cannot be greater than (although it may be equal to) its symmetry number (). (5) Faces of double bonds, carbonium ions, and molecules with disubstituted atoms capable of accepting a third ligand (e.g., R-S-R) are homotopic if they interchange through a C2 axis. 5. Stereoheterotopic ligands The stereoheterotopic ligands are of two types: enantiotopic if their positions in the molecule are related in mirror-image fashion and diastereotopic if their positions do not bear a mirror-image relationship. 5.1 Enantiotopic ligands and faces Enantiotopic ligands and faces may be recognized by the application of the substitution-
Load more

Recommended publications
  • Enantiotopicity, Diastereotopicity
    Stereochemistry and stereocontrolled synthesis (OC 8) A lecture from Prof. Paul Knochel, Ludwig-Maximilians-Universität München WS 2015-16 1 Wichtig! • Prüfung Stereochemistry 02. Februar 2016 8:00 – 10:00 Willstätter-HS • Nachholklausur Stereochemistry 5. April 2016 9:00 – 11:00 Willstätter-HS 2 Problem set part I 3 Problem set part II 4 Problem set part III 5 Recommended Literature • E. Juaristi, Stereochemistry and Conformational Analysis, Wiley, 1991. • E. Eliel, Stereochemistry of Organic Compounds, Wiley, 1994. • A. Koskinen, Asymmetric Synthesis of Natural Products, Wiley, 1993. • R. Noyori, Asymmetric Catalysis, Wiley, 1994. • F. A. Carey, R. J. Sundberg, Advanced Organic Chemistry, 5th Edition, Springer, 2007. • A. N. Collins, G. N. Sheldrake, J. Crosby, Chirality in Industrie, Vol. I and II, Wiley, 1995 and 1997. • G.Q. Lin, Y.-M. Li, A.S.C. Chan, Asymmetric Synthesis, 2001, ISBN 0-471-40027-0. • P. Deslongchamps, Stereoelectronic Effects in Organic Chemistry, Pergamon, 1983. • M. Nogradi, Stereoselective Synthesis, VCH, 1995. • E. Winterfeldt, Stereoselective Synthese, Vieweg, 1988. • R. Mahrwald (Ed.), Modern Aldol Reactions, Vol. I and II, Wiley, 2004. • C. Wolf, Dynamic Stereochemistry of Chiral Compounds, RSC Publishing, 2008. • A. Berkessel, H. Gröger, Asymmetric Organocatalysis, Wiley-VCH, 2005. • J. Christoffers, A. Baro (Eds.), Quaternary Stereocenters, Wiley-VCH, 2005. • Catalytic Asymmetric Synthesis, I. Oshima (Ed.), Wiley, 2010. 6 Recent advances of asymmetric catalysis 7 Asymmetric Hydrogenation of Heterocyclic Compounds 8 R. Kuwano, N. Kameyama, R. Ikeda, J. Am. Chem. Soc. 2011, 133, 7312-7315. Camphor-Derived Organocatalytic Synthesis of Chromanones 9 Z.-Q. Rong, Y. Li, G.-Q. Yang, S.-L. You, Synlett 2011, 1033-1037.
    [Show full text]
  • Enantiotopic Discrimination in the NMR Spectrum of Prochiral Solutes in Chiral Liquid Crystals
    Chemical Society Reviews Enantiotopic Discrimination in the NMR Spectrum of Prochiral Solutes in Chiral Liquid Crystals Journal: Chemical Society Reviews Manuscript ID: CS-REV-07-2014-000260 Article Type: Review Article Date Submitted by the Author: 29-Jul-2014 Complete List of Authors: Lesot, Phillippe; Universite Paris Sud (Paris XI), LRMN, ICMMO, UMR 8182 Aroulanda, Christie; Universite Paris Sud (Paris XI), LRMN, ICMMO, UMR 8182 Zimmermann, Herbert; Abteilung Biophysik, Max-Planck-Institut für Medizinische Forschung, Luz, Zeev; Weizmann Institute of Science, Department of Chemical Physics Page 1 of 117 Chemical Society Reviews Chem. Soc. Rev. (2014) - 1 - Enantiotopic Discrimination in the NMR Spectrum of Prochiral Solutes in Chiral Liquid Crystals Philippe Lesot* ,a , Christie Aroulanda a, Herbert Zimmermann b and Zeev Luz c a Laboratoire de RMN en Milieu Orienté CNRS UMR 8182, ICMMO, Bât. 410, Université de Paris-Sud, 91405 Orsay cedex, France. bAbteilung Biophysik, Max-Planck-Institut für Medizinische Forschung, Jahnstrasse 29, 69120 Heidelberg, Germany. c Weizmann Institute of Science, Department of Chemical Physics, Rehovot 76100, Israel. Corresponding author : Philippe Lesot: [email protected] Keywords : Prochirality, Enantiotopic sites, NMR, Chiral Liquid Crystals, Dynamics. Type of article : (comprehensive) review Chemical Society Reviews Page 2 of 117 Chem. Soc. Rev. (2014) - 2 - Abstract The splitting of signals in the NMR spectra originating from enantiotopic sites in prochiral molecules when dissolved in chiral solvents is referred to as spectral enantiotopic discrimination. The phenomenon is particularly noticeable in chiral liquid crystals (CLC) due to the combined effect of the anisotropic magnetic interactions and the ordering of the solute in the mesophase.
    [Show full text]
  • The Control of Stereochemistry by the Pentafluorosulfanyl Group
    Organic & Biomolecular Chemistry View Article Online PAPER View Journal | View Issue The control of stereochemistry by the pentafluorosulfanyl group† Cite this: Org. Biomol. Chem., 2018, 16, 3151 Paul R. Savoie, Cortney N. von Hahmann, Alexander Penger, Zheng Wei and John T. Welch * The influence of pentafluorosulfanylation on biological activity has been revealed in numerous compara- tive studies of biologically active compounds, but considerably less is known about the influence of pen- tafluorosulfanylation on reactivity. Among the distinctive properties of the pentafluorosulfanyl group is the profound dipole moment that results from introduction of this substituent. It has been shown that dipolar Received 20th December 2017, effects coupled with the steric demand of the SF5 group may be employed to influence the stereo- Accepted 3rd April 2018 chemistry of reactions, especially those processes with significant charge separation in the transition DOI: 10.1039/c7ob03146g state. The Staudinger ketene-imine cycloaddition reaction is an ideal platform for investigation of dipolar rsc.li/obc control of diastereoselectivity by the pentafluorosulfanyl group. Introduction ation into a hydrocarbon chain, the restricted rotation about the carbon–sulfur bond that results from interactions with Numerous pentafluorosulfanyl(SF5)-containing organic nearby methylene groups, can lead to localized conformational – compounds1 10 have been prepared that have potential utility rigidity of the alkyl chain.21,22 in drug discovery, agrochemical synthesis and materials
    [Show full text]
  • Chapter 8. Chiral Catalysts José M
    Chapter 8. Chiral Catalysts José M. Fraile, José I. García, José A. Mayoral 1. The Origin of Enantioselectivity in Catalytic Processes: the Nanoscale of Enantioselective Catalysis. Enantiomerically pure compounds are extremely important in fields such as medicine and pharmacy, nutrition, or materials with optical properties. Among the different methods to obtain enantiomerically pure compounds, asymmetric catalysis1 is probably the most interesting and challenging, in fact one single molecule of chiral catalyst can transfer its chiral information to thousands or even millions of new chiral molecules. Enantioselective reactions are the result of the competition between different possible diastereomeric reaction pathways, through diastereomeric transition states, when the prochiral substrate complexed to the chiral catalyst reacts with the corresponding reagent. The efficiency of the chirality transfer, measured as enantiomeric excess [% ee = (R−S)/(R+S) × 100], depends on electronic and steric factors in a very subtle form. A simple calculation shows that differences in energy of only 2 kcal/mol between these transition states are enough to obtain more than 90% ee, and small changes in any of the participants in the catalytic process can modify significantly this difference in energy. Those modifications may occur in the near environment of the catalytic centre, at less than 1 nm scale, but also at longer distances in the catalyst, substrate, reagent, solvent, or support in the case of immobilized catalysts. This is the reason because asymmetric
    [Show full text]
  • Synthesis and Enzymatic Resolution of Amino Acid Esters in "Green" Solvents — Ionic Liquids
    Copyright Warning & Restrictions The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted material. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specified conditions is that the photocopy or reproduction is not to be “used for any purpose other than private study, scholarship, or research.” If a, user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of “fair use” that user may be liable for copyright infringement, This institution reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law. Please Note: The author retains the copyright while the New Jersey Institute of Technology reserves the right to distribute this thesis or dissertation Printing note: If you do not wish to print this page, then select “Pages from: first page # to: last page #” on the print dialog screen The Van Houten library has removed some of the personal information and all signatures from the approval page and biographical sketches of theses and dissertations in order to protect the identity of NJIT graduates and faculty. ABSTRACT SYNTHESIS AND ENZYMATIC RESOLUTION OF AMINO ACID ESTERS IN "GREEN" SOLVENTS — IONIC LIQUIDS By Hua Zhao Chiral separation has attracted tremendous attention in pharmaceutical and chemical fields, especially in the area of chiral drug development. Chiral amino acids are among the most important intermediates in the asymmetric synthesis of modern drugs.
    [Show full text]
  • Stereochemistry
    Lecture note- 2 Organic Chemistry CHE 502 STEREOCHEMISTRY DEPARTMENT OF CHEMISTRY UTTARAKHAND OPEN UNIVERSITY UNIT 4: STEREOCHEMISTRY 1 CONTENTS 4.1 Objectives 4.2 Introduction 4.3 Isomerism 4.4 Structural (Constitutional) Isomerism 4.5 Stereo (Configurational) isomerism 4.5.1 Geometrical Isomerism 4.5.2 Optical Isomerism 4.6 Element of Symmetry 4.7 Stereogenic centre (Stereogenicity) 4.7.1 Optical activity and Enantiomerism 4.7.2 Properties of enantiomerism 4.7.3 Chiral and achiral molecules with two stereogenic centers 4.7.4 Diastereomers 4.7.5 Properties of Diastereomers 4.7.6 Erythro (syn) Threo (anti) diastereomers 4.7.7 Meso compounds 4.8 Relative and absolute configurations 4.8.1 D/L nomenclature 4.8.2 R/S nomenclature 4.8.3 Sequence Rule 4.9 Newman and sawhorse projection formulae 4.10 Fisher flying and wedge formulae 4.11 Racemic mixture (racemates) 4.12 Quasi enantiomers 4.13 Quasi racemates 4.14 Stereochemistry of allenes, spiranes, biphenyls, ansa compounds, cyclophanes and related compounds 4.15 Summary 4.16 Terminal Questions 4.17 Answers 4.1 OBJECTIVES In this unit learner will be able to: ➢ Depict various types of isomerism exhibited by organic compounds and their representation ➢ Analyze the three dimensional depictions of organic compounds and their two dimensional representations. ➢ Learn Stereogenicity, chirality, enantiomerism, diastereomerism, their relative and absolute configurations ➢ Learn about the various stereo chemical descriptors such as (cis-trans, E/Z, D/L, d/l, erythro/threo, R/S and syn/anti) given to organic molecules differ ➢ Describe the stereochemistry of various rigid and complex molecules like spiranes, adamentanes, catenanes, cyclophanes etc.
    [Show full text]
  • Chirality in Organic Molecules
    M. U. en Química, Universitat de València 44606 - Advanced Organic Chemistry Prof. Pablo Gaviña Unit 2 Stereochemistry, stereoselectivity and stereoelectronic effects Recommended textbooks: - Francis. A. Carey, Richard J. Sundberg, Advanced Organic Chemistry. Part A: Structure and Mechanisms, 5th Edition, Springer. - F. A. Carroll, Perspectives on Structure and Mechanism in Organic Chemistry, 2nd Ed., 2010, Wiley 1 - Basic concepts of isomerism and stereoisomerism - Symmetry of organic molecules. Elements of symmetry. - Reasons of chirality in organic molecules. Stereogenic elements. Nomenclature. - Diastereoisomerism. - Prostereoisomerism and prochirality: topicity and its descriptors. - Conformational analysis. Stereoelectronic effects. - Influence of configuration and conformation on the reactivity of organic molecules. - Stereoselectivity and stereospecifity of organic reactions. 2 General concepts of isomerism and stereoisomerism Qualitative elementary composition: C, H, O Quantitative chemical composition: C 66.66%, H 11.11%, O 22.22% Empirical formula: (C4H8O)n Molecular mass: 72, n = 1 Molecular formula: C4H8O Constitution of the molecule: Nature and bonding of its atoms. Structure: Constitution and stereochemistry (configuration and conformation) Isomers: -Constitutional -Stereoisomerism -Configurational isomers -Conformers (C4H8O)n 3 CONSTITUTIONAL ISOMERISM AND STEREOISOMERISM Isomers are chemical compounds that have the same molecular formula but differ in the constitution or arrangement of their atoms in space. ISOMERS Constitutional
    [Show full text]
  • Stereochemistry and Stereoselective Synthesis
    www.ShimiPedia.ir www.ShimiPedia.ir László Poppe and Mihály Nógrádi Editors László Poppe, József Nagy, Gábor Hornyánszky and Zoltán Boros Contributing Authors Stereochemistry and Stereoselective Synthesis www.ShimiPedia.ir www.ShimiPedia.ir Edited by László Poppe and Mihály Nógrádi Contributing Authors László Poppe, József Nagy, Gábor Hornyánszky and Zoltán Boros Stereochemistry and Stereoselective Synthesis An Introduction www.ShimiPedia.ir Editors All books published by Wiley-VCH are carefully produced. Nevertheless, authors, Dr. László Poppe editors, and publisher do not warrant the Budapest Univ. of Technology & information contained in these books, Economics including this book, to be free of errors. Dept. of Organic Chemistry & Readers are advised to keep in mind that Technology statements, data, illustrations, procedural Szt. Gellért tér 4 details or other items may inadvertently 1111 Budapest be inaccurate. Hungary Library of Congress Card No.: applied for Dr. Mihály Nógrádi Budapest Univ. of Technology & British Library Cataloguing-in-Publication Economics Data Dept. of Organic Chemistry & A catalogue record for this book is avail- Technology able from the British Library. Szt. Gellért tér 4 1111 Budapest Hungary Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek Contributing Authors lists this publication in the Deutsche Dr. László Poppe Nationalbibliografie; detailed Budapest Univ. of Technology & bibliographic data are available on the Economics Internet at <http://dnb.d-nb.de>. Dept. of Organic Chemistry & Technology © 2016 Wiley-VCH Verlag GmbH & Co. Szt. Gellért tér 4 KGaA, Boschstr. 12, 69469 Weinheim, 1111 Budapest Germany Hungary All rights reserved (including those of Dr. József Nagy translation into other languages). No part Budapest Univ.
    [Show full text]
  • Bsc Chemistry
    Subject Chemistry Paper No and Title 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No and 19; Prostereoisomerism (Prochirality) Title Module Tag CHE_P1_M19 CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No. 19: Prostereoisomerism (Prochirality) TABLE OF CONTENTS 1. Learning Outcomes 2. Introduction 2.1 Molecular Symmetry and Chirality 2.2 What is prochirality? 3. Homotopic and Heterotopic Ligands and Faces 3.1 Topicity of Ligands and Faces 3.2 Homotopic Ligands and Faces 3.3 Heterotopic Ligands and Faces 4. Summary CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module No. 19: Prostereoisomerism (Prochirality) 1. Learning Outcomes After studying this module, you shall be able to Understand the connection between molecular symmetry and chirality. Differentiate between chiral and prochiral molecule. Know the difference between homotopic and heterotopic ligands and faces. To identify the prochirality in molecules. Identify the different type of stereotopic ligands and faces in the molecules. 2. Introduction 2.1 Molecular Symmetry and Chirality A molecule (or an object) can have only one mirror image. If the image is superimposable on the original, the molecule is called achiral. On the other hand, if it is not superimposable on the original, the molecule and its mirror image form two distinct species called enantiomers, giving rise to a type of stereoisomerism known as enantiomerism. Such molecules are called chiral and the two enantiomers are said to differ in their sense of chirality or handedness in the same way as right hand differs from the left hand. Three terms have almost been used interchangeably to describe molecules, which show enantiomerism: asymmetric, dissymmetric, and chiral.
    [Show full text]
  • Applications of Imino-Diels–Alder Reactions in Synthesis
    Applications of Imino-Diels–Alder Reactions in Synthesis A thesis presented by Jasprit Kaur Chahal As partial fulfilment of the requirements for the award of the degree of Doctor Philosophy of Imperial College London Thorpe Laboratory Department of Chemistry Imperial College London South Kensington Campus London SW7 2AZ 1 Declaration of Originality The work reported in this thesis is my own and information derived from the published and unpublished work of others has been appropriately referenced. 2 Abstract The aim of the project was to synthesise (−)-morphine utilising a tethered intramolecular imino-Diels–Alder reaction. This thesis begins by providing brief reviews on the subjects of total synthesis of morphine and asymmetric imino-Diels–Alder reaction. The major section focuses on the research findings in the past four years. Starting with investigations in the development of a novel stereoselective imino-Diels–Alder reaction of methyl propargyl ether derived (1 E, 3Z)-1-silyloxy-3-(phenylthio)-1,3- dienes with trans -2-phenylcyclohexyl glyoxylate derived N-tosylimine. Following with the progress made so far to synthesise triene II; this was envisaged to be prepared from the enantiomerically pure alcohol III and allylic halide IV. The alcohol III was prepared in a five-step sequence from p-anisaldehyde. However, the synthesis of the allylic halide IV from D-lyxose was more challenging and problematic. Initial efforts for its synthesis via a route incorporating the Ohira–Bestmann reaction caused an unwanted epimerisation. Further efforts, through an eleven-step sequence including Wittig dibromomethylenation and intramolecular ene–yne metathesis gave V or VI . However, the reductive eliminations to give the alcohol precursor to IV were unsuccessful.
    [Show full text]
  • Thesis-Alieh
    CORE Metadata, citation and similar papers at core.ac.uk Provided by University of Saskatchewan's Research Archive ALDOL COUPLINGS OF CHIRAL FRAGMENTS WITH KINETIC RESOLUTION: SCOPE AND LIMITATIONS A thesis submitted to the College of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in the Department of Chemistry University of Saskatchewan Saskatoon by Alieh Kazemeini © Copyright Alieh Kazemeini December, 2011. All rights reserved. Permission to Use In presenting this thesis in partial fulfillment of the requirements for a Postgraduate degree from the University of Saskatchewan, I agree that the Libraries of this University may make this thesis freely available for inspection. I further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor or professors who supervised the thesis work, or in their absence, by the Head of the Department, or the Dean of the College in which the thesis work was done. It is understood that any copying or publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition will be given to me and to the University of Saskatchewan in any scholarly use which may be made of any material in this thesis. Requests for permission to copy or to make other use of material in this thesis in whole or in part should be addressed to: The Head Department of Chemistry University of Saskatchewan 110 Science Place Saskatoon, SK S7N 5C9 CANADA i Acknowledgements First of all, I would like to express my deepest and greatest gratitude to my supervisor, Dr.
    [Show full text]
  • Preview Chapter 6 on Stereochemistry in PDF Format
    CHAPTER 6 Stereochemistry Intent and Purpose Stereochemistry is the study of the static and dynamic aspects of the three-dimensional shapes of molecules. It has long provided a foundation for understanding structure and re- activity. At the same time, stereochemistry constitutes an intrinsically interesting research field in its own right. Many chemists find this area of study fascinating due simply to the aes- thetic beauty associated with chemical structures, and the intriguing ability to combine the fields of geometry, topology, and chemistry in the study of three-dimensional shapes. In ad- dition, there are extremely important practical ramifications of stereochemistry. Nature is inherently chiral because the building blocks of life (␣-amino acids, nucleotides, and sugars) are chiral and appear in nature in enantiomerically pure forms. Hence, any substances cre- ated by humankind to interact with or modify nature are interacting with a chiral environ- ment. This is an important issue for bioorganic chemists, and a practical issue for pharma- ceutical chemists. The Food and Drug Administration (FDA) now requires that drugs be produced in enantiomerically pure forms, or that rigorous tests be performed to ensure that both enantiomers are safe. In addition, stereochemistry is highly relevant to unnatural systems. As we will de- scribe herein, the properties of synthetic polymers are extremely dependent upon the stereo- chemistry of the repeating units. Finally, the study of stereochemistry can be used to probe reaction mechanisms, and we will explore the stereochemical outcome of reactions through- out the chapters in parts II and III of this text. Hence, understanding stereochemistry is nec- essary for most fields of chemistry, making this chapter one of paramount importance.
    [Show full text]