Question

which of the following alkyl halides is most likely to undergo rearrangement in an sn1 reaction?
3 - bromopentane
2 - chloro - 3,3 - dimethylpentane
1 - bromo - 4 - methylcyclohexane
3 - chloropentane
bromocyclohexane

Explanation:

Step1: Understand SN1 reaction

In SN1 reaction, carbocation formation occurs.

Step2: Analyze carbocation stability

Carbocation stability: tertiary > secondary > primary.
For 2 - chloro - 3,3 - dimethylpentane, after losing Cl⁻, it forms a tertiary carbocation.
Other compounds like 3 - bromopentane forms secondary carbocation, 1 - bromo - 4 - methylcyclohexane forms secondary carbocation (if considering ring - opening etc. in some cases but less stable than tertiary here), 3 - chloropentane forms secondary carbocation and bromocyclohexane forms secondary carbocation. Tertiary carbocation is more likely to undergo rearrangement (due to higher energy state and tendency to get more stable) compared to secondary and primary carbocations formed from other alkyl halides.

Answer:

2 - chloro - 3,3 - dimethylpentane