Chapter 4, Problem 33P

Interpretation Introduction

Interpretation:

The structure(s) with which the absolute configuration of $\text{(-)-bromochlorofluoromethane}$ matches is to be discussed.

Concept introduction:

An absolute configuration is the three-dimensional spatial arrangement of atoms or groups at the chirality center.

The absolute configuration at the chiral center is assigned on the basis of Cahn-Ingold-Prelog rules. The Cahn-Ingold-Prelog system ranks substituents at the chirality center in the order of decreasing atomic number. The next step is to orient the molecules so that the bond to the lowest ranked substituent points away from the observer and to determine if the sequence of decreasing priority of the other three substituents is clockwise or counterclockwise.

If this path is clockwise, the absolute configuration is R. If this path is counterclockwise, the absolute configuration is S.

In Fischer projections, the molecule is oriented so that the two vertical bonds at the chirality center are directed away from the viewer and the two horizontal bonds point toward the viewer.

When the connection between absolute configuration and sign of rotation is known, it is a common practice to incorporate both in the name of the compound.