Consider the S _ N 1 solvolysis of the following halides in aqueous formic acid: (i) (ii) (iii) (iv) Which of the following represents the correct decreasing order of their reactivity?

Step-by-step solution

The rate of S _ N 1 solvolysis depends on the stability of the carbocation intermediate formed in the rate-determining step. The more stable the carbocation, the faster the reaction. Let us analyze the carbocations formed by the departure of the bromide ion from each compound: For (i), the departure of Br ⁻ yields a secondary alkyl carbocation, CH ₃- CH ( CH ₃)- CH ⁺- CH ₃ . This carbocation is stabilized by hyperconjugation with 4 -hydrogens. For (ii), the departure of Br ⁻ yields a tertiary alkyl carbocation ( 1