Chapter 26.1, Problem 1P

Interpretation Introduction

Interpretation:

The chirality centers in the two non-standard amino acids shown are to be located, and their absolute configurations to be determined using Cahn-Ingold-Prelog R, S notation.

Concept Introduction:

Chirality centers in a molecule are the carbon atoms that have four different atoms/group bonded to them. These carbons are ${\text{sp}}^{\text{3}}$ hybridized.

Cahn-Ingold-Prelog rules assign priorities to the four atoms directly bonded to the chirality center on the basis of their atomic numbers.

The higher the atomic number, higher the priority.

In case two or more of these atoms have the same atomic number, the atoms bonded to them are compared.

After assigning the priorities, the molecule is oriented, so that the atom/group with the least priority (#4) is at the back, pointing away from the observer. Then, if the first three groups are arranged in a clockwise manner, the configuration of the center is R. If they are arranged counterclockwise, the configuration is S.