Q5-71E - Organic Chemistry (Mcmurry)

Question

How many stereoisomers of 2,4-dibromo-3-chloropentane are there? Draw them, and indicate which are optically active.

Step-by-Step Solution

Answer

There are four stereoisomers of 2,4-dibromo-3-chloropentane. Optical activity is represented in the structure given below:

Step 1: Structures of stereoisomers

For the compound, 2,4-dibromo-3-chloropentane, four stereoisomers can be drawn. They are represented as A, B, C and D as given below:

Step 2: Optical activity of the stereoisomers

From the structures, it is clear that C and D are enantiomers because they are mirror images but cannot be superimposed. So they are optically active. But A and B are non-superimposable non-mirror images. Thus A and B are diastereoisomers. But they are meso compounds because they are achiral. So A and B are optically inactive. 

Thus A and B are optically inactive while C and D are optically active.