Question

Which compound of the following pairs give fast SN1 reaction

Answer 1

Answer:

(I), i.e. 2-chloro-2-methylpropane, undergoes faster SN1 reaction than (II) i.e., 3-chloropentane. The alkyl halide (I) is 2° while (II) is 1°. 2° carbocation is more stable than 1° carbocation. Therefore, (I), 2-chloroheptane, undergoes faster SN1 reaction than (II), 1-chlorohexane.

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Answer 2

Answer:

Faster SN1 reaction is implied by better stability of carbocation formed after removing the leaving group (in this case halogen)

1. CH₃-O-CH₂-Cl > CH₃-O-CH₂-CH₂-Cl

        REASON : -OCH₃ provides a better inductive (+I) effect than -CH₃

    2. CH₃=CH₃-CH₂-CH₂-Cl < CH₃-CH₃=CH₂-CH₂-Cl

        REASON : the stability of allylic carbocation due to delocalisation  (or resonance)

    3. (CH₃)₃-C-CH₂-Cl > CH₃-CH₂-Cl

        REASON : more +I effect of 3° carbon than 1° carbon

    4. Chlorocyclohexane > bi-cyclo compound (in the picture)

        REASON : unstable nature of bridgehead carbocation (refer bredt's rule)

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