ABC26OR0021 · General Organic Chemistry
Subject: Organic Chemistry · Chapter: General Organic Chemistry · Topic: Conformational Analysis · Exam: CSIR-NET JUNE 2013 · Marks: 2 · Difficulty: Medium
The most stable conformations of 1, 2-difluoroethane and dl-2, 3-butanediol are 
(a)
and
and(b)
and
and(c)
and
and(d)
Answer
Answer (as printed): D
Explanation
In case of $\mathrm{F\text{-}CH_2\text{-}CH_2\text{-}F}$, Gauche conformation is stable due to Gauche effect i.e. hyper conjugation. Gauche effect refers to the phenomenon that the gauche conformer is energetically more stable than the anti-conformer in 1,2 dihaloethanes ($\mathrm{X\text{-}CH_2\text{-}CH_2\text{-}X}$).