Haloalkanes and Haloarenes - Result Question 40
####40. Which of the following biphenyls is optically active?
[2016]
(a)
(b)
(c)
(d)
Show Answer
Solution:
- (b)
In option (a), there is no chiral carbon.
In option (c), there exist a center of symmetry.
In option (d), there exist a plane of symmetry.
In option (d), both the rings are not in the same plane and the rotation is restricted around the single bond.
Restricted rotation Biphenyl compounds are devoid of individual chiral carbon atoms, but $o$-substituted biphenyl show optical isomerism. This is due to the fact that, both the rings are not in the same plane because of steric hindrance of the groups present in $o$ position. Also, these groups restrict the rotation around the single bond and hence they must exist in two non-super imposable mirror images of each other.
