Chapter 4.9, Problem 13P

Interpretation Introduction

Interpretation:

The chiral center in the molecular model of thalidomide is to be identified and its absolute configuration as R or S is to be determined.

Concept introduction:

When a tetrahedral carbon atom is connected to four different atoms or groups, then that carbon is called a chiral carbon or chiral center.

The absolute configuration is the three-dimensional spatial arrangement of substituents attached to a chiral center.

The Cahn-Ingold-Prelog rule system lists the substituents bonded to the chiral center in the order of decreasing atomic number. A higher atomic number has a higher priority over a lower atomic number for the substituent.

When there are two identical atoms directly attached to the chirality center, then they are ranked on the basis of the atomic numbers of the other atoms attached to them.

If an atom has multiple bonds, it is considered to be replicated as a substituent on that atom.

If isotopes are present, they are ranked on the basis of their atomic masses.

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

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

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