Ch_322a_5.09

Ch_322a_5.09 - Synthesis of Enantiomers In many synthetic...

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Synthesis of Enantiomers In many synthetic procedures, achiral starting materials produce chiral products . In the absence of chiral influences, the chiral product is produced in a racemic form : 50% (S) and 50% (R). Examples CH 3 CH 2 CH 2 CH 3 achiral Br 2 CH 3 CH 2 CHBrCH 3 * chiral 50% (S), 50% (R) a racemic form CH 3 CH 2 CCH 3 O = achiral + H 2 Ni CH 3 CH 2 CHCH 3 OH * chiral 50% (S), 50% (R) a racemic form
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Symmetrical Reaction Pathways Racemic forms of chiral products result whenever a reaction goes through an achiral stage : starting point or chemical intermediate. An achiral stage introduces symmetrical reaction pathways that necessarily lead to 50% (S) and 50% (R) chiral products.
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Example: Reduction of 2-Butanone CH 3 CH 2 CCH 3 O = + H 2 C=O CH 3 CH 3 CH 2 O=C CH 3 CH 2 CH 3 H-H H-H These and other mirror image modes of reaction occur with equal probability. C H OH CH 3 CH 2 CH 3 (R) C CH 3 CH 2 CH 3 HO H (S) 50% 50% Racemic Form
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Enantioselective Reactions A reaction that produces a stereocenter where one enantiomer is
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This note was uploaded on 07/22/2009 for the course CHEM 322AL taught by Professor Jung during the Summer '07 term at USC.

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Ch_322a_5.09 - Synthesis of Enantiomers In many synthetic...

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