Question

Considering the following set of reaction sequences,

• A. P is Q is and T is
• B. P is Q is and T is
• C. P is S is cyclohexyl methyl ketone and T is
• D. P is and Q is formed by treatment of with .

Answer 1

Answer: (A)

A

Answer 2

The question describes a reaction scheme. Let's analyze each option, assuming the starting alkene is 1-methylcyclohexene (C$_7$H$_{12}$).

• Option A:

  • P: 1-bromo-2-methylcyclohexane (formed by anti-Markovnikov addition of HBr).

  • Q: 2-methylcyclohexan-1-ol (formed by hydroboration-oxidation, which is anti-Markovnikov addition of water).

  • R: Oxidation of 2-methylcyclohexan-1-ol (a secondary alcohol) yields 2-methylcyclohexanone (S).

  • T: Reaction of 2-methylcyclohexanone with MeMgBr followed by hydrolysis gives 1,2-dimethylcyclohexan-1-ol. Dehydration with 20% H$_3$PO$_4$ at 360 K yields primarily 1,2-dimethylcyclohexene (Saytzeff product).

  The structures of P, Q, and T in option A are consistent with the reactions starting from 1-methylcyclohexene.

• Option B:

  • Q: Formed by hydration of 1-methylcyclohexene with H$_2$O/H$^+$ (acid-catalyzed hydration, Markovnikov addition). This would yield 1-methylcyclohexan-1-ol (a tertiary alcohol). Tertiary alcohols do not undergo oxidation with Jones reagent. Thus, S is not formed as a ketone. Option B is incorrect.

• Option C:

  • S is given as cyclohexyl methyl ketone. If R is oxidized to S, and S is cyclohexyl methyl ketone, then R must be 1-cyclohexylethan-1-ol (secondary alcohol). If R is 1-cyclohexylethan-1-ol, and it is formed from Q, which is formed from the starting alkene (1-methylcyclohexene), this sequence does not seem consistent. If the starting alkene is 1-methylcyclohexene, Q is 2-methylcyclohexan-1-ol or 1-methylcyclohexan-1-ol. Neither of these upon oxidation gives cyclohexyl methyl ketone. So option C is incorrect.

• Option D:

  • If P is 1-bromo-2-ethylcyclohexane, formed by anti-Markovnikov addition of HBr, the starting alkene must be 1-ethylcyclohexene. However, the subsequent reactions in option D are not consistent with the scheme.

Given the options, it seems the question intends for the starting material to be 1-methylcyclohexene (C$_7$H$_{12}$), despite stating C$_8$H$_{14}$. With this assumption, option A is correct.