Q. 30 E-c - Organic Chemistry (Mcmurry)

Question

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

Step-by-Step Solution

Answer

(c).  S configuration

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.

Step 2: Identify the need of interchange.

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

Step 3: 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.