Concept: A carboxyl group is a functional group with the formula -COOH. Organic acids containing this group are called carboxylic acids. We need to identify which of the given compounds lacks this -COOH group. Step 1: Structure/Nature of the given compounds
(1) Tartaric acid: This is a dicarboxylic acid (contains two -COOH groups). Its formula is , or HOOC-CH(OH)-CH(OH)-COOH. It clearly contains carboxyl groups.
(2) Picric acid: The chemical name for picric acid is 2,4,6-trinitrophenol. Its structure consists of a phenol group (-OH attached to a benzene ring) with three nitro groups (- ) attached to the benzene ring at positions 2, 4, and 6. Phenol structure: . Picric acid structure: . It contains a hydroxyl (-OH) group and nitro groups, but no carboxyl (-COOH) group. Despite its name "acid," its acidity comes from the phenolic -OH group, whose acidity is enhanced by the electron-withdrawing nitro groups.
(3) Malonic acid: This is a dicarboxylic acid with the formula CH (COOH) or HOOC-CH -COOH. It clearly contains carboxyl groups.
(4) Lactic acid: This is -hydroxypropanoic acid. Its formula is CH CH(OH)COOH. It contains one carboxyl group and one hydroxyl group. Step 2: Identify the compound without a carboxyl group
From the structures:
Tartaric acid: Has -COOH groups.
Picric acid: Has -OH (phenolic) and - groups, but NO -COOH group.
Malonic acid: Has -COOH groups.
Lactic acid: Has a -COOH group. Therefore, Picric acid does not contain a carboxyl group.