Question

Assign R or S configurations to the chirality centers in the following molecules (blue = N)

Short answer

(b). R configuration

Step-by-step solution

Step 1:Rules for R/S nomenclature when molecule drawn as perspective formula are 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 hatched wedge,and

(ii) between the remaining two groups.

4. Draw an arrow from 1 to 3 via 2.

Convert the given structure into atomic form

The red spheres represent oxygen, blue spheres represent nitrogen, black spheres—carbon, and grey spheres—hydrogen.

Assign the ranking.

In this case assign the ranking according to the atomic numbers of the functional group attached to the chiral center.

Assign the configuration

In this case the fourth priority is at dashed bond. So, there is no need of double interchange. Hence, the configuration of the chiral center is R.