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JEE Main 2025 Jan 22 Shift 2, Chemistry Q5: Properties of Alkanes

JEE Main2025Jan 22, Shift 2Chemistry
Q.

When sec-butylcyclohexane reacts with bromine in the presence of sunlight, the major product is :

  1. A

    1

  2. B

    2

  3. C

    3

  4. D

    4

Solution

Free-radical bromination with is highly selective: the propagation step generates the most stable carbon radical.

In sec-butylcyclohexane, the carbon of the side chain that is attached to the cyclohexane ring is a tertiary . Abstraction of this hydrogen gives a tertiary free radical, which is the most stable among all available radical positions (tertiary secondary primary).

Bromine then couples with this radical to give the product in which Br sits on the tertiary carbon of the sec-butyl group, as shown in option (4).

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