Concept:The electrophilic addition of hydrogen halides to unsymmetrical alkenes follows Markovnikov's rule, driven by the stability of the intermediate carbocation.
Formula:$$ (\text{CH}_3)_2\text{C}=\text{CH}_2 + \text{HBr} \rightarrow (\text{CH}_3)_3\text{C}-\text{Br} $$
Solution:- Isobutylene (2-methylpropene) has the structure \( (\text{CH}_3)_2\text{C}=\text{CH}_2 \).
- The electrophile (\( \text{H}^+ \)) adds to the terminal \( \text{CH}_2 \) carbon because this forms a tertiary carbocation at the central carbon, which is highly stabilized by hyperconjugation and the inductive effect.
- The bromide ion (\( \text{Br}^- \)) then attacks this tertiary carbocation.
- The resulting product is 2-bromo-2-methylpropane, commonly known as tert-butyl bromide.
Why other options are incorrect:- Isobutyl bromide would be the anti-Markovnikov product, requiring peroxides.
- n-butyl and sec-butyl bromides form from the addition to straight-chain butenes, not the branched isobutylene.
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