Which one of the following drawings shows trans-1-bromo-3-ethylcyclohexane in its highest energy conformation?
(A) (B)
(C) (D)

Question

Which one of the following drawings shows trans-1-bromo-3-ethylcyclohexane in its highest energy conformation? (A) (B) (C) (D)

TestHub · Accepted Answer

First pick out the trans-1,3 drawings : (A) is cis (both substituents up, diaxial), (C) has the substituents 1,2 (wrong connectivity); (B) and (D) are trans-1,3. Of the two trans chairs, the higher energy one carries the larger group axial : the ethyl group (A-value ~7.5 kJ/mol) costs more axial than Br (~1.8 kJ/mol). (B) has ethyl axial and Br equatorial - the highest energy conformation.

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