Question

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

Short answer

1. S- configuration

Step-by-step solution

Rules for R/S nomenclature when molecule drawn as perspective formula

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 counter clockwise, the centre is in the S configuration.

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

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

(ii) between the two remaining groups

4. Draw a line 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 priority.

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 not at dashed bond. So, there is a need of double interchange.After double interchange. the configuration of the chiral center is S.