Chapter 5A

G any 14 disubstituted cyclohexane the cyclic analogy

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Unformatted text preview: tereocenters RRR RRS RSR SRR SSS SSR SRS RSS Diastereomers Enantiomers 8 Stereoisomers (maximum): 4 Diastereomeric pairs of enantiomers. Generally: n Stereocenters give rise to a maximum of 2n stereoisomers, e.g. 2, 4, 8, 16, 32... Note: Stereocenters need not be adjacent for these relationships to hold: Stereochemistry in Chemical Reactions Ground Rule: We cannot get excess of one enantiomer from achiral starting material or from a racemate. I.e., we cannot "generate" optical activity (unless we use a "chiral handle") Br2, hv -HBr * Br Chiral, but racemic 50:50 mix of R and S achiral achiral medium When the starting material is enantiomerically pure or enriched (and therefore optically active) and H abstraction occurs at stereocenter: Products are racemic and not optically active. Br C CH3 H C CH3 H Cl2 Same environment Note: If you start from a rac...
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This note was uploaded on 03/21/2012 for the course CHEM 140A taught by Professor Whiteshell during the Fall '04 term at UCSD.

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