Q6 · CSIR NET Chemistry, June 2016
Paper: CSIR NET June 2016 · Subject: Organic Chemistry · Chapter: General Organic Chemistry · Topic: Conformational Analysis · Marks: 2 · Difficulty: Medium
The correct statements about conformations X and Y of 2-butanone are 
(X) 
(Y) (A) X is more stable than Y (B) Y is more stable than X (C) Methyl groups in X are anti (D) Methyl groups in Y are gauche
(X) (Y) (A) X is more stable than Y (B) Y is more stable than X (C) Methyl groups in X are anti (D) Methyl groups in Y are gauche(a)A and D
(b)A and C
(c)B and C
(d)A, C and D
Answer
Answer: D ✓ checked by 4AB · confidence medium
Explanation
Butanone prefers the conformer with the C-4 methyl eclipsing the C=O oxygen (X), where it is anti to the acyl CH₃. In Y the two methyls are gauche. A, C and D (d).
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