What is the predominant mechanism for the reaction between 2-bromo-2-methylpropane and warm aqueous sodium hydroxide?
Answer and explanation
Correct answer: C. SN1 (unimolecular nucleophilic substitution)
- Step 1: 2-bromo-2-methylpropane is a tertiary haloalkane (3-degree alkyl halide).
- Step 2: Steric hindrance prevents direct backside nucleophilic attack required by SN2.
- Step 3: Ionization of the C-Br bond forms a stable tertiary carbocation in the rate-determining step.
- Step 4: Hydroxide ion attacks the carbocation rapidly, characteristic of the SN1 mechanism.
Answer
SN1 (unimolecular nucleophilic substitution).
Why not the others: 'SN2 (bimolecular nucleophilic substitution)' occurs predominantly in primary haloalkanes due to minimal steric hindrance; 'Electrophilic addition' occurs in alkenes and alkynes; 'Free radical substitution' requires UV light and homolytic cleavage in alkanes.
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