IR Spectroscopy Identifies Carbonyl Formation via KMnO4 Oxidation

Steps:

• S shows no 1700-1740 cm⁻¹ absorption, confirming no C=O group.
• T shows 1700-1740 cm⁻¹ absorption for C=O, 1620 cm⁻¹ for C=C, and lacks 2500-3500 cm⁻¹ broad band, excluding O-H in acids/alcohols.
• Hot, concentrated KMnO4 oxidizes unsaturated compounds like aromatics or alkenes to carbonyls without O-H if cleavage avoids aldehydic intermediates.
• Match to B: benzene (S) lacks C=O; yields ketone (T) consistent with oxidation product profile.

Why B is correct:

• Benzene's aromatic ring undergoes KMnO4 oxidation to ketones like butan-2-one in specific natural compound contexts, adding C=O without broad O-H per IR.

Why the others are wrong:

• A: Propane oxidation yields carboxylic acid (not aldehyde), showing broad O-H absorption.
• C: S (acetophenone) has C=O absorption at 1700-1740 cm⁻¹, contradicting S's IR.
• D: T (malonic acid) has broad O-H absorption 2500-3500 cm⁻¹ from COOH groups.

Final answer: B