Assign R or S configuration to each chirality center in pseudoephedrine, an over-the-counter decongestant found in cold remedies (blue = N)

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 dashedbond:

▪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:

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

(ii) between the remaining two groups.

▪Draw an arrow from 1 to 3 via 2.

Red sphere representsoxygen,black spheres—carbon,and grey spheresrepresenthydrogen.

According to the representation of the atoms, draw the structure of the compound.

There are two chiral centre presents in the molecule C₁ and C_2.

According to the atomic numbers of the groups attached to the chiral center,assign the priority to the atoms attached.

As fourth priority is in solid bond position, there is a need of double interchange as per the given rules. After double interchange the configuration of C₁, chiral center is R and C₂ chiral center is S.