Question

Orient each of the following drawings so that the lowest-ranked group is toward the rear, and then assign R or S configuration

Short answer

(c). S configuration

Step-by-step solution

Step 1:Rules for R/S nomenclature when molecule drawn as perspective formulaare given below.

1. Determine the priority of the atoms or groups bonded to the chiral center and label them as 1, 2 3, and 4.

2. If the lowest priority (4) group is bonded by a dashed bond:

▪Draw an arrow from 1 to 3 via 2.

If the arrow points clockwise, then the centre has the R configuration.

If the arrow points counter-clockwise, then the centre has the S configuration.

3. If the lowest priority (4) group is not bonded by a dashed bond:

▪Make double interchange:

(i) between 4 and group bonded by wedge, and

(ii) between the remaining two groups.

▪Draw an arrow from 1 to 3 via 2.

Identify the need of interchange.

As ranking is already given and fourth priority is not in dashed position, there isneed for double interchange.

Assign the configuration.

After the interchange, fourth priority is in dashed position anddirection of the arrow is clock wise. So, the configuration of given compounds is S.