Chapter 4.10, Problem 15P

Interpretation Introduction

Interpretation:

For the four isomeric $\text{2,3-dihydroxybutanoic acids}$ shown in preceding Fischer projection, the $\text{R}$ and $\text{S}$ to the chirality centers are to be assigned.

Concept introduction:

The absolute configuration is the three dimensional spatial arrangement of substituents at the chiral center.

The R and S configuration at the chiral center is assigned on the basis of Cahn-Ingold-Prelog rules.

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.

In Fischer projections, the molecule is oriented such that the vertical bonds attached to the chiral center are directed away from the observer and the horizontal bonds point towards the observer.

When two groups are exchanged in a Fischer projection, it reverses the configuration of the chiral center.

Enantiomers are the mirror images of each other; they have opposite configuration at the each chirality center.

Diastereomers have at least two chiral centers and they are not mirror images of each other; they must have an opposite configuration for at least one chirality centers.