See image — Aldehydes Ketones and Carboxylic Acids Chemistry Question

💡 Solution & Explanation

Concept: Reductive amination / intramolecular cyclization under hydrogenation conditions. Step 1 – Identify the starting material: The substrate is 2-(3-aminopropyl)cyclohexan-1-one. It contains a ketone (cyclohexanone) and a primary amine (-NH2) tethered by a three-carbon chain at the alpha position of the ketone. Step 2 – Intramolecular imine (Schiff base) formation: Under the reaction conditions (H2 / Raney Ni), the amine and ketone first undergo intramolecular condensation. The NH2 attacks the carbonyl carbon of the cyclohexanone to form a hemiaminal, then loses water to give a cyclic imine (Schiff base). Counting the atoms in the ring: the carbonyl carbon (C1 of cyclohexane) + C2 of cyclohexane (bearing the chain) + CH2-CH2-CH2-N forms a 6-membered ring fused to the remaining 4 carbons of the cyclohexane ring. This gives a bicyclic imine intermediate where a six-membered nitrogen-containing ring (with a C=N double bond) is fused to the cyclohexane ring — i.e., a Δ1,9-octahydroisoquinoline skeleton. Step 3 – Hydrogenation: H2 / Raney Ni reduces the C=N double bond of the imine to give the fully saturated bicyclic amine. The product is decahydroisoquinoline (also called octahydroisoquinoline in some numbering schemes), a bicyclic compound with both rings fully saturated and nitrogen at the ring junction, bearing one N-H. Step 4 – Match to options: - Option (a): bicyclic oxygen-containing compound (chromene skeleton) — wrong heteroatom, not formed here. - Option (b): 1,2,3,4-tetrahydroquinoline has a benzene ring (aromatic) fused to a piperidine; no aromatic ring can form from saturated starting material under these conditions. - Option (c): decahydro (fully saturated) isoquinoline — both rings are saturated, nitrogen present with N-H. This matches the product of intramolecular reductive amination of the given substrate. Correct. - Option (d): dihydroquinoline contains an aromatic benzene ring and a partially unsaturated N-ring; again, aromatization is not possible here. The intramolecular reductive amination of 2-(3-aminopropyl)cyclohexan-1-one gives a fully saturated bicyclic secondary amine corresponding to decahydroisoquinoline (option c). Therefore, the correct answer is C.