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

1 Answer
Jan 10, 2016

Answer:

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

Bond-line

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.

Four
#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.

Three