Chapter 26.2, Problem 2P

Interpretation Introduction

Interpretation:

The absolute configuration (R or S) at the $\text{α-carbon}$ atom in each of the given L-amino acids is to be determined.

Concept Introduction:

The absolute configuration of a chirality center is its three dimensional spatial arrangement of substituents attached to it.

When determining the configuration of a chiral center, the atoms or groups attached to it are first assigned priorities on the basis of their atomic numbers.

If two atoms attached to the chiral center have the same atomic number, then they are compared on the basis of the atomic numbers of the atoms attached to them.

The molecule is oriented such that the lowest ranked group points away from the observer.

If the remaining three groups in order of the decreasing priority trace a clockwise path, the configuration is R.

If the remaining three groups in order of the decreasing priority trace a counter clockwise path, the configuration is S.