Q104 · CSIR-NET Chemistry, June 2013
Paper: CSIR-NET June 2013 · Subject: Organic Chemistry · Chapter: Stereochemistry · Topic: Stereochemistry – General · Marks: 2 · Difficulty: Medium
The most stable conformations of 1, 2-difluoroethane and dl-2, 3-butanediol are
(a)
and [second sketch not cut — see note]
and [second sketch not cut — see note](b)
and 
and (c)
and 
and (d)
and 
and Answer
Answer: D ✓ checked by 4AB · confidence high
Explanation
1,2-Difluoroethane prefers gauche (gauche effect, σC–H → σ*C–F). In dl-2,3-butanediol, the conformer with gauche OH groups (intramolecular H-bond) and anti methyls is most stable (d).
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