Question

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

Answer 1

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

`"C1"` and `"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.

`color(white)(XXX)"A"color(white)(XXXXXl) "B"color(white)(XXXXXXll) "C"color(white)(XXXXXll) "D"`

5. Identify meso compounds

`"A"` and `"B"` are the same meso compound because they have an internal mirror plane passing through `"C4"` and the midpoint of the `"C1-C2"` bond.

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