Question

The maximum number of isomers (including stereoisomers) that are possible on mono-chlorination of the following compound is ___:

Answer 1

Let us list down the products that could be obtained via free radical monochlorination:

Here, although we have listed different constitutional isomers, stereoisomers have not been explicitly mentioned. If you look at the structure A, the third carbon C3 accompanies a “star” (asterisk) to indicate that the carbon is chiral. With one chiral centre, there will be two stereoisomers – one with an “S” configuration and its non-superimposable mirror image with “R” configuration.

Likewise, for structure B, there will be 4 stereoisomers (2S-3S, 2R-3R, 2R-3S, 2S-3R) because there are 2 chiral centres. The remaining unlabelled structures (bottom two) do not have any chirality involved. So, in all we have 2 + 4 + 1 + 1 = 8 possible monochlorination products (including stereoisomers).