Ch_322a_4.018

Ch_322a_4.018 - Relative Stabilities of Chair Conformations...

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Relative Stabilities of Chair Conformations As with methylcyclohexane, the conformations are analyzed to identify gauche interactions . The conformation with the fewer such interactions is more stable and will dominate in the chair-chair equilibrium. Which chair conformation of trans -1,4-dimethylcyclohexane is more stable? CH 3 CH 3 H H A diequatorial CH 3 CH 3 H H B diaxial H H H H no gauche interactions 2x2 = 4 gauche interactions Chair A, the diequatorial conformation, is more stable by 4 gauche interactions or 4 x 0.9 = 3.6 kcal/mol and will dominate in the chair-chair equilibrium.
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Which is the more stable chair conformation of trans -1-tertiary-butyl-3-methylcyclohexane? First draw one chair conformation with the substituents in the 1 and 3 positions and in the trans stereochemistry. CH 3 -C CH 3 CH 3 CH 3 H H Then, draw the second chair conformation. CH 3 -C CH 3 CH 3 H CH 3 H A B Evaluate the elements of steric strain in each chair conformation. In A, the larger tert-butyl group is equatorial while the smaller
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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_4.018 - Relative Stabilities of Chair Conformations...

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