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Question
Explain primary benzylic halide shows higher reactivity by SN1 mechanism than other primary alkyl halide.
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Solution
- SN1 reaction involves the formation of a carbocation intermediate. The benzylic carbocation intermediate formed are resonance stabilized, and hence SN1 mechanism is favoured.
- Resonance stabilization of benzylic carbocation can be represented as:
- Reactivity order of alkyl halides towards SN1 mechanism is 3° > 2° > 1° > CH3X. That is, SN1 mechanism is least favoured in primary alkyl halides.
- Benzylic carbocation formed is more stable than the primary carbocation; therefore, primary benzylic halide shows higher reactivity by SN1 mechanism than other primary alkyl halide.
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