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NEET CHEMISTRYHydrocarbonsMedium

Question

HCl with an alkene X reacts in accordance with Markovnikov’s rule to give 1-Chloro-1-methylcyclohexane. The structure of alkene (X) is:

A

(Structure of 1-Methylcyclohexene)

B

(Structure of Methylenecyclohexane)

C

(1) and (2)

D

(Structure Missing)

Step-by-Step Solution

  1. Analyze the Reaction: The reaction involves the electrophilic addition of HCl to an alkene (X) to form a tertiary alkyl halide: 1-Chloro-1-methylcyclohexane.
  2. Markovnikov's Rule: The rule states that the negative part of the addendum (Cl⁻) attaches to the carbon atom possessing fewer hydrogen atoms, while the hydrogen (H⁺) attaches to the carbon with more hydrogen atoms. Mechanistically, the reaction proceeds via the most stable carbocation intermediate [NCERT 11th, Ch 13, Sec 13.3.4; NCERT 12th, Ch 10, Sec 10.4.2].
  3. Product Analysis: The product has a chlorine atom and a methyl group on the same carbon (C1) of the cyclohexane ring. This implies the intermediate was a stable tertiary carbocation at C1.
  4. Identify Precursors (Alkene X):
  • Case 1 (1-Methylcyclohexene): Protonation of the double bond (between C1 and C2) occurs at C2 to generate the stable tertiary carbocation at C1. Attack by Cl⁻ yields the product.
  • Case 2 (Methylenecyclohexane): Protonation of the exocyclic double bond (between ring C and external CH₂) occurs at the CH₂ group to generate the same stable tertiary carbocation at the ring carbon. Attack by Cl⁻ yields the same product.
  1. Conclusion: Both 1-Methylcyclohexene and Methylenecyclohexane can serve as Alkene X.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Hydrocarbons. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYHydrocarbonsalkenereactsaccordancemarkovnikovschloromethylcyclohexane

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