Question

Which of the following does not contain a carboxyl group : \(-COOH\)

• A. Tartaric acid
• B. Picric acid
• C. Malonic acid
• D. Lactic acid

Hint:

A carboxyl group is -COOH.
Tartaric acid, Malonic acid, Lactic acid are all carboxylic acids (they have -COOH).
{Picric acid} is actually 2,4,6-trinitro{phenol}. Phenols have an -OH group directly attached to a benzene ring. Picric acid's acidity comes from this phenolic -OH group (made stronger by the nitro groups), not from a -COOH group. So, Picric acid does not contain a carboxyl (-COOH) group.

Answer 1

The Correct Option is B

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 \(\text{C}_4\text{H}_6\text{O}_6\), 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 (-\(\text{NO}_2\)) attached to the benzene ring at positions 2, 4, and 6. Phenol structure: \(\text{C}_6\text{H}_5\text{OH}\). Picric acid structure: \(\text{C}_6\text{H}_2(\text{NO}_2)_3\text{OH}\). 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\(_2\)(COOH)\(_2\) or HOOC-CH\(_2\)-COOH. It clearly contains carboxyl groups.
(4) Lactic acid: This is \(\alpha\)-hydroxypropanoic acid. Its formula is CH\(_3\)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 -\(\text{NO}_2\) 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.