Q6 · CSIR NET Chemistry, June 2018
Paper: CSIR NET June 2018 · Subject: Organic Chemistry · Chapter: General Organic Chemistry · Topic: Conformational Analysis · Marks: 2 · Difficulty: Medium
The correct statement about the following compounds is: 
A 
B
A B(a)A is more stable than B
(b)B is more stable than A
(c)A and B are equally stable
(d)A and B are both locked conformations
Answer
Answer (as printed): C
Explanation
A is trans-9,10-dimethyldecalin and B is cis-9,10-dimethyldecalin. Count gauche-butane interactions. A: trans-decalin itself has none, but each angular methyl is axial to both rings (4 gauche each), and the two methyls are anti: 8 in total. B: cis-decalin itself has 3; each angular methyl is axial to one ring (2 gauche each), and the two cis methyls are gauche to each other (1): 3 + 2 + 2 + 1 = 8. Equal strain, so A and B are equally stable (c).
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