Oxidative Cleavage Differences in Terpenes

Steps:

• Limonene has an endocyclic trisubstituted alkene and an exocyclic 1-methylethenyl group; α-terpinene has conjugated dienes in the ring with methyl and isopropyl substituents.
• Hot concentrated KMnO4 cleaves C=C bonds: =CR2 → ketone, =CHR → carboxylic acid, =CH2 → CO2.
• Limonene cleavage yields a diketo acid (acetone unit becomes methyl ketone, ring opens to keto-acid chain).
• Terpinene cleavage yields a different diketo acid due to conjugated system and substituent positions, resulting in distinct carbonyl placements.

Why B is correct:

• KMnO4 oxidation cleaves double bonds based on substitution, producing unique diketo acids from limonene's isolated alkenes vs. terpinene's conjugated dienes (structural isomerism dictates product formula).

Why the others are wrong:

• A: Both hydrogenate to identical p-menthane (1-isopropyl-4-methylcyclohexane), so same compound.
• C: Br2 addition yields stereoisomers, not positional; chiral carbons vary (limonene product has 2, terpinene may differ).

Final answer: B