Which of the following alkyl halides reacts FASTEST via an nucleophilic substitution mechanism?
Answer and explanation
Correct answer: C. (1-bromobutane)
- Step 1: In the mechanism, the rate-determining transition state is crowded and highly sensitive to steric hindrance around the electrophilic carbon.
- Step 2: The reactivity order of alkyl halides in is methyl .
- Step 3: 1-Bromobutane is an unbranched primary () alkyl halide with minimal steric bulk, allowing the fastest nucleophilic backside approach.
Answer
(1-bromobutane).
Why not the others: 2-Bromobutane is a secondary () alkyl halide with greater steric shielding; 2-Bromo-2-methylpropane is a tertiary () alkyl halide that does not undergo ; 1-Bromo-2-methylpropane has steric crowding from the adjacent -methyl branch.
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