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

(a). S configuration

Step-by-step solution

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

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

2. If the lowest priority (4) group is bonded with a dashed bond, draw an arrow from 1 to 3 via 2.

• The center has the R configuration if the arrow points clockwise.
• Whenever the arrow points anticlockwise, the center is in the S configuration.

3. Make a double interchange if the lowest priority (4) group is not bound by a dashed bond:

A hatched wedge connects the four and the group in (i)

(ii) between the two remaining groups

4. Draw a line from 1 to 3 via 2.

Assign the configuration.

As ranking is already given and fourth priority is in dashed position,there is no need for double interchange.

Arrow rotates towards anti-clockwise direction.

Hence, the configuration of compounds is S.