The major product of the following reaction is: (CH3)2CH-CH=CH2 + HBr ->[(C6H5CO)2O2] ?

NEET 2021 · ChemistryPrevious Year Question

The major product of the following reaction is: $(CH X_{3}) X_{2} CH - CH = CH X_{2} + HBr (C X_{6} H X_{5} CO) X_{2} O X_{2} ?$

Answer: (C) (C) $(CH X_{3}) X_{2} CH - CH X_{2} - CH X_{2} Br$ . Benzoyl peroxide $(C X_{6} H X_{5} CO) X_{2} O X_{2}$ initiates a free-radical chain (peroxide / Kharasch effect), so HBr adds anti-Markovnikov.

A.(A) $(CH X_{3}) X_{2} CH - CHBr - CH X_{3}$
B.(B) $(CH X_{3}) X_{2} CBr - CH X_{2} - CH X_{3}$
C.(C) $(CH X_{3}) X_{2} CH - CH X_{2} - CH X_{2} Br$ ✓
D.(D) $(CH X_{3}) X_{2} CH - CH X_{2} - CH X_{2} - COCH X_{3}$

Correct Answer

Solution & Explanation

Benzoyl peroxide $(C X_{6} H X_{5} CO) X_{2} O X_{2}$ initiates a free-radical chain (peroxide / Kharasch effect), so HBr adds anti-Markovnikov. The Br adds to the terminal (less substituted) carbon, giving the more stable secondary radical intermediate, so the product is the primary bromide $(CH X_{3}) X_{2} CH - CH X_{2} - CH X_{2} Br$ (1-bromo-3-methylbutane). The peroxide effect operates only with HBr, not HCl or HI.

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The major product of the following reaction is: $(CH X_{3}) X_{2} CH - CH = CH X_{2} + HBr (C X_{6} H X_{5} CO) X_{2} O X_{2} ?$