Question

Label each compound as R or S.

a.

b.

c.

d.

Short answer

a. S isomer.

b. S isomer.

c. R isomer.

d. S isomer.

Step-by-step solution

R and S nomenclature

The R and S nomenclature is assigned to the given molecule as follows:

• The molecules having high molecular masses are given as the first priority.

The order of the priority of some groups is: $\text{H<C<N<O<S<Cl<Br<I}$

• The double bonded groups also have the highest priority because it is multiplied by the same group in the place of a bond. For example, C=O is equivalent to CC-OO.

• The clockwise movement based on the priority gives R configuration, and the anticlockwise movement gives S configuration.

If the lowest priority group is above the plane, then the R is inverted into S and vice versa.

Explanation

a. The order of priority is shown as:

${\text{Br>Cl>CH}}_3\text{>H}$

Therefore, the movement is anticlockwise.

Representation of S isomer

b. The order of priority is shown as:

${\text{OH>COOH>CH}}_3\text{>H}$

Therefore, the movement is anticlockwise.

Representation of S isomer

c. The order of priority is shown as:

${\text{CH}}_2{\text{CH}}_2{\text{CH(CH}}_3{\text{)CH>CH}}_2{\text{CH}}_2{\text{CH}}_2{\text{CH}}_2{\text{>CH}}_3\text{>H}$

Therefore, the movement is clockwise.

Representation of R isomer

d. The order of priority is shown as:

${\text{OH>CH}}_2{\text{Cl>CH}}_2{\text{CH}}_2{\text{Br>CH}}_3$

Therefore, the movement is clockwise.

Representation of S isomer