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

(b). R configuration

Step-by-step solution

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

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

(ii) between the two remaining groups.

4. Draw a line 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 in dashed position, anddirection of the arrow is clock wise. So, the configuration of given compounds is R.