See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Step 1 – Analyze reaction (a): Starting material: cyclopropanecarboxylic acid. Path 1: SOCl2 converts -CO2H to acid chloride, then NH3 gives primary amide, then KOBr (Hofmann degradation) gives cyclopropylamine, then HNO2 (diazotization then loss of N2) gives cyclopropyl carbocation/carbene-like intermediate. The cyclopropylamine + HNO2 generates diazonium which loses N2 (option s). The Hofmann rearrangement involves migration from carbon to electron-deficient nitrogen (option q). The cyclopropylcarbene/carbocation intermediate can ring-open to give allene or rearrange, and ultimately an aromatic compound can form (option p). So (a) matches p, q, s. Step 2 – Analyze reaction (b): Dicyclopropylacetylene reacts with a cyclopropyl carbene precursor (cyclopropyl-C(=N2)-Cl) under hv. Photolysis of a diazo compound (C with N2 group) generates a carbene (option r) with loss of N2 (option s). The carbene can react with the alkyne and cyclopropyl groups. Cyclopropylcarbene is known to ring-open to give vinylcarbene and ultimately cyclopentadienyl/aromatic species (option p). So (b) matches p, r, s. Step 3 – Analyze reaction (c): Phi-CHCl2 with t-BuOK undergoes elimination of two HCl molecules to generate phenylcarbene (dichlorocarbene intermediate or direct carbene, option r). The product (A) is phenylcarbene or benzyne. phi-C≡C-phi (diphenylacetylene) with AlCl3: this is a Friedel-Crafts type cyclization of diphenylacetylene which gives an aromatic compound, specifically triphenylene or fluoranthene-type product (option p). No N2 evolution, no migration to nitrogen. So (c) matches p, r. Step 4 – Analyze reaction (d): The substrate is a sterically hindered aromatic amide (ortho-substituted with NO2 groups and bulky naphthalene). KOBr is the reagent for Hofmann rearrangement (-CONH2 → -NH2 with loss of CO2 equivalent). The Hofmann rearrangement involves migration from carbon to electron-deficient nitrogen (option q). The resulting amine in this highly conjugated, constrained system would form an aromatic product (option p). So (d) matches p, q. Step 5 – Verify no cross-matches are missed: - (a): p (aromatic formed after rearrangement/ring opening), q (Hofmann: C→N migration), s (N2 from HNO2 + amine) ✓ - (b): p (aromatic from cyclopropylcarbene ring opening), r (carbene formed from diazo photolysis), s (N2 lost from diazo compound) ✓ - (c): p (aromatic product from AlCl3 cyclization of diphenylacetylene), r (carbene from phi-CHCl2 + t-BuOK) ✓ - (d): p (aromatic amine product), q (Hofmann: migration C→N) ✓ Therefore, the correct answer is {"a": ["P", "Q", "S"], "b": ["P", "R", "S"], "c": ["P", "R"], "d": ["P", "Q"]}.