Question

What are the total number of stereoisomers of 2,3-dichlorobutane?

Answer 1

There are three stereoisomers of 2,3-dichlorobutane.

Explanation:

The structure of 2,3-dichlorobutane is `"CH"_3stackrelcolor(blue)("*")("C")"HCl"stackrelcolor (blue)("*")("C")"HClCH"_3`

The two carbon atoms marked with blue asterisks are chiral centres.

The maximum number of stereoisomers is `2^n`, where `n` is the number of chiral centres.

Since `n = 2`, the maximum number of stereoisomers is `2^2 = 4`.

We can write the four possible Fischer structures as

Structures 1 and 2 are two different nonsuperimposable mirror images of each other.

But Structures 3 and 4 are meso compounds.

They are superimposable on each other, so they are the same compound.

So, there are only three stereoisomers of 2,3-dichlorobutane.