# How many stereoisomers are possible for 1,2-dichlorocyclopentane?

Jan 10, 2016

There are three stereoisomers for 1,2-dichlorocyclopentane.

#### Explanation:

Here's the procedure I would follow.

1. Draw the bond-line structure.
2. Identify the chiral centres.
3. Calculate the maximum number of possible stereoisomers.
4. Draw them.
5. Eliminate any meso compounds.

1. Bond-line structure

The bond-line structure is

2. Chiral centres

$\text{C1}$ and $\text{C2}$ are chiral centres.

3. Maximum number of stereoisomers

There are two chiral carbons, so the maximum number of stereoisomers is ${2}^{2} = 4$.

4. Possible stereoisomers

Draw "UpUp" and its mirror image, then "UpDown" and its mirror image.

$\textcolor{w h i t e}{X X X} \text{A"color(white)(XXXXXl) "B"color(white)(XXXXXXll) "C"color(white)(XXXXXll) "D}$

5. Identify meso compounds

$\text{A}$ and $\text{B}$ are the same meso compound because they have an internal mirror plane passing through $\text{C4}$ and the midpoint of the $\text{C1-C2}$ bond.

Hence there are only three stereoisomers of 1,2-dichlorocyclopentane.