Question

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

• A.
• B.
• C.
• D.

Hint:

In free radical substitution reactions, the most stable free radical intermediate determines the major product. In this case, the benzylic position is the most stable and thus the bromine will attach there.

Answer 1

The Correct Option is B

To identify the main product of sec-butylcyclohexane's reaction with bromine under sunlight, we analyze the reaction mechanism.

1. Reaction Type: This is a free radical halogenation. Sunlight generates free radicals, causing hydrogen atoms on the aliphatic chain to be replaced by bromine atoms.
2. Radical Stability: Bromine radicals preferentially remove hydrogen from the position yielding the most stable radical. For cyclohexane derivatives, radical stability follows this order: Tertiary>Secondary>Primary.
   • Tertiary radical > Secondary radical > Primary radical
3. Application to Sec-Butylcyclohexane: The tertiary carbon on the sec-butyl group in sec-butylcyclohexane is the most likely site for radical formation due to its superior stability compared to other potential radicals. Hydrogen abstraction from this tertiary carbon results in the most stable radical intermediate.
4. Major Product Formation: Following the formation of the most stable radical, a bromine atom attaches to it, yielding the major product. This substitution occurs at the tertiary carbon of the sec-butyl group.
5. Conclusion: Consequently, the major product is formed by substituting bromine at the tertiary carbon of the sec-butyl group.

This corresponds to the major product depicted in the accompanying image.