Question

The relative configurations of the stereoisomers of tartaric acid were established by the following synthesis:

(1) D-(+)-glyceraldehydediastereomers A and B (separated)

(2) Hydrolysis of A and B using aqueous Ba(OH)₂ gave C and D, respectively.

(3) HNO₃ oxidation of C and D gave (-)-tartaric acid and meso-tartaric acid, respectively.

(a) You know the absolute configuration of D-(+)-glyceraldehyde, Use Fischer projections to show the absolute configurations of products A, B, C, and D.

(b) Show the absolute configurations of the three stereoisomers of tartaric acid: (+)-tartaric acid, (-)-tartaric acid, and meso-tartaric acid.

Short answer

(a) Formation of products A, B, C and D from (+)-glyceraldehyde:

(b)

Step-by-step solution

Explanation of part (a):

D-(+)-glyceraldehyde on treatment with hydrogen cyanide generates diastereomeric pair of which A and B are products.

Cyanide ion acts as a nucleophile and attacks at the planar carbonyl carbon of aldehyde which generates products in which position of hydroxyl group is on either side. Hydrolysis of A and B using barium hydroxide will lead to the formation of C and D products. Cyano group changes to carboxylic group on basic hydrolysis. Further, oxidation with nitric acid is carried out and it will oxidise alcoholic functional group to acid as nitric acid is a strong oxidising agent and you get (-)-tartaric acid and meso-tartaric acid from C and D respectively.

Formation of products A, B, C and D from (+)-glyceraldehyde

Explanation of part (b):

Absolute configuration is defined for the chiral molecular entities. Stereochemical descriptions include “R” and “S” which stands for Rectus and Sinister respectively. Absolute configuration of a substituent in a molecule is independent of the atoms of groups.