See image — Haloalkanes and Haloarenes Chemistry Question

💡 Solution & Explanation

Concept: Alcoholic KOH promotes E2 elimination of HBr from alkyl halides to give alkenes. The key question is what alkene product forms from each positional isomer of bromocyclohexanone. Reaction (1) - 2-bromocyclohexan-1-one: The bromine is at C2 (alpha to the carbonyl). E2 elimination can occur by removing a proton from C1 (not possible, carbonyl carbon) or C3. Removing H from C3 gives the enone: cyclohex-2-en-1-one (2-cyclohexenone). Alternatively, the alpha-bromo ketone can undergo elimination toward the carbonyl to give the conjugated enone, which is the thermodynamically favored product. Product A = 2-cyclohexen-1-one (cyclohex-2-enone). Reaction (2) - 3-bromocyclohexan-1-one: The bromine is at C3. E2 elimination: removing H from C2 gives the conjugated enone 2-cyclohexen-1-one (more stable, conjugated double bond). Removing H from C4 gives the non-conjugated 3-cyclohexen-1-one (less stable). By Zaitsev's rule and thermodynamic preference for conjugation, the major product is 2-cyclohexen-1-one. Product B = 2-cyclohexen-1-one. Reaction (3) - 4-bromocyclohexan-1-one: The bromine is at C4. E2 elimination: removing H from C3 or C5 gives 3-cyclohexen-1-one (non-conjugated). However, under alc. KOH conditions, the initially formed non-conjugated alkene can isomerize, or the base can promote isomerization of the double bond into conjugation with the carbonyl. The thermodynamic product under basic conditions is the conjugated 2-cyclohexen-1-one. Thus Product C = 2-cyclohexen-1-one. All three reactions produce 2-cyclohexen-1-one as the major product because: (1) direct elimination gives conjugated enone; (2) elimination preferentially gives conjugated enone; (3) the double bond migrates into conjugation with the carbonyl under basic conditions. Hence A = B = C. Why other options fail: Options (a), (b), (c) each suggest one product differs, but in all cases the thermodynamic sink is the same conjugated enone 2-cyclohexen-1-one, making all products identical. Therefore, the correct answer is D.