In 5-3, you drew the enantiomers for a number of chiral

Solution 7P

Rules to assign the R and S configuration to the compounds is as follows:

1. First select the chiral center, and give the priority to the groups around the symmetric carbon atom (chiral carbon).

2. If the priority of the groups from highest to lowest is in clockwise direction, then the chiral center has R configuration.

3. If the priority of the groups from highest to lowest is in anti-clockwise direction, then the chiral center has S configuration.

4. The lowest priority group must be in below the plane (i.e. represented with dashed line).

(a)

The given compound is pentan-2-ol. Pentan-2-ol has one asymmetric carbon atom. It is indicated with blue colour.

Calculate the number of stereoisomers by using the following formula

Number of stereoisomers =

Here, n is number of asymmetric carbon atoms.

So, the number of stereoisomers for the compound pentan-2-ol is = 2 stereoisomers .

The two stereoisomers of pentan-2-ol are as follows:

The two stereoisomers are mirror images of each other. So, the two isomers are enantiomers.

Now, assign the R and S configuration to the two stereoisomers is as follows:

Thus, the two enantiomers of pentan-2-ol with R and S configuration are shown below:

(b)

The given compound is pentan-3-ol. Pentan-3-ol has no asymmetric carbon atoms.

Thus, the compound is pentan-3-ol is achiral.

(c)

The given compound is alanine. Alanine has one symmetric carbon. This is indicated with blue colour.

So, the number of stereoisomers for the compound alanine is = 2 stereoisomers ..

The two stereoisomers of alanine are shown below: