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Topic: Alkenes: geometrical isomerism, electrophilic addition, Markovnikov and peroxide effect· Hydrocarbons

The major product of the following chemical reaction is :(CH_3)_2CH-CH=CH_2 + HBr (C_6H_5CO)_2O_2 ?

The major product of the following chemical reaction is :

\((CH_3)_2CH-CH=CH_2 + HBr \xrightarrow{(C_6H_5CO)_2O_2} ?\)

reaction of 3-methylbut-1-ene with HBr/peroxide and four structure options

1. \((CH_3)_2CH-CH_2-CH_2-Br\)

2. \((CH_3)_2CH-CH_2-CH_2-O-COC_6H_5\)

3. \((CH_3)_2CH-CH(Br)-CH_3\)

4. \((CH_3)_2CBr-CH_2-CH_3\)

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Answer: 1. \((CH_3)_2CH-CH_2-CH_2-Br\)

Key idea: with peroxide, HBr adds to alkenes by a free-radical path: anti-Markovnikov (Kharasch peroxide effect).

The \(\mathrm{Br\cdot}\) radical attacks the terminal \(\mathrm{CH_2}\) of 3-methylbut-1-ene, giving the more stable secondary radical. Then H is picked up from HBr, so Br sits on the terminal carbon:

\(\mathrm{(CH_3)_2CH-CH_2-CH_2-Br}\) (1-bromo-3-methylbutane).

Options 3 and 4 are the Markovnikov products (no peroxide); option 2 is an ester, not formed.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report
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