Isomerism & Stereochem_lower level

Isomerism & Stereochem_lower level - Classification...

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L. D. Shirtcliff – CHEM 3053 Isomerism Classical Definitions of Isomerism: Isomers are compounds that have identical molecular formulae but differ in the nature or sequence of bonding of their atoms or in the spatial arrangement of their atoms. Constitutional Isomers differ in the nature or sequence of bonding of their atoms. Stereoisomers have the same sequence of bonding, but differ as to the spatial arrangement of their atoms. Stereochemical Terminology A molecule (or other object) is chiral or dissymmetric if it possesses no alternating symmetry axes (S n - rotation/reflection). (Such a condition makes the chiral molecule nonsuperimposable on its mirror image.) The property is called chirality . (Note that optical activity is a measurable; chirality is not.) An achiral molecule does possess an S n and is superimposable on its mirror image.
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Unformatted text preview: Classification of Stereoisomers (two separate classification schemes): (1) Enantiomers (the word defines a relationship) are stereoisomers which are nonsuperimposable mirror images of one another. They are said to be enantiomeric . (Chirality is the necessary and sufficient condition for the existence of enantiomers.) Diastereoisomers (= Diastereomers) are stereoisomers that are not enantiomers. (2) Configurational Stereoisomers (= Configurations) are stereoisomers which are interconvertable only by breaking and reforming bonds. Conformational Stereoisomers (= Conformations) are stereoisomers which are interconvertable without bond breaking (rotations about formal single bonds, nitrogen inversion, pseudorotation of ligands about heteroatoms, and rotation about partial double bonds are all allowed)....
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This note was uploaded on 12/22/2011 for the course CHEM 3053 taught by Professor Laurashirtcliff during the Fall '11 term at Oklahoma State.

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