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In an SN1 reaction (e.g., tert-butyl bromide + OH⁻):
AThe reaction inverts configuration completely
BThere is no intermediate
CThe rate is first order (depends only on [R-X]); proceeds via slow ionisation to a carbocation, then fast attack by nucleophile
DThe rate is second order — depends on both alkyl halide and nucleophile
Answer & Solution
Correct answer: C. The rate is first order (depends only on [R-X]); proceeds via slow ionisation to a carbocation, then fast attack by nucleophile
**SN1 = unimolecular nucleophilic substitution**. **Rate ∝ [R-X] only** (first order). Two-step mechanism: (i) slow ionisation to **carbocation** + X⁻ (rate-determining), (ii) fast nucleophile attack. Carbocation is planar (sp²) → attack from either face → **racemisation** in chiral substrates.
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