Question

The IUPAC name of tartaric acid is:

• A. 1,3-dihydroxybutane-1,4-dioic acid
• B. 2,3-dihydroxybutane-1,4-dioic acid
• C. 2,3-dihydroxy-4-butanoic acid
• D. 2,2-dihydroxy-4-butanoic acid

Hint:

Tartaric acid is known for its two hydroxyl groups and its role in the formation of salts and esters used in various industrial applications, including in the production of wine.

Answer 1

The Correct Option is B

Naming tartaric acid systematically starts with drawing out its four-carbon skeleton and numbering it so the principal characteristic group, the two -COOH carbons, get the lowest possible locants.

1. 1,3-dihydroxybutane-1,4-dioic acid: Since the suffix "-1,4-dioic acid" already fixes carbons 1 and 4 as the carboxylic acid carbons, carbon 1 cannot simultaneously be listed as carrying a hydroxyl group, so this name contradicts itself.
2. 2,3-dihydroxybutane-1,4-dioic acid: Numbering the chain HOOC(C1)-CHOH(C2)-CHOH(C3)-COOH(C4) places the carboxyl groups correctly at C1 and C4, and the two hydroxyl groups correctly at C2 and C3, which is a full, correct systematic name for tartaric acid's actual structure.
3. 2,3-dihydroxy-4-butanoic acid: "Butanoic acid" names a four-carbon chain with a single carboxylic acid, but tartaric acid needs a dicarboxylic acid name to account for both -COOH groups, so this suffix under-describes the molecule.
4. 2,2-dihydroxy-4-butanoic acid: Both hydroxyls on one carbon (C2) would describe a gem-diol, an unstable arrangement that does not match tartaric acid's vicinal diol structure, and again the monoacid suffix leaves out the second carboxylic acid group.

Since only the 2,3-dihydroxybutane-1,4-dioic acid name correctly places both carboxylic acids at the chain ends and both hydroxyls on the two middle carbons, the correct answer is 2,3-dihydroxybutane-1,4-dioic acid.