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 an S _ N 1 solvolysis reaction depends on the stability of the intermediate carbocation formed after the departure of the leaving group (halide ion). Let us analyze the carbocations formed from each of the given substrates: 1. Halide (i) forms a secondary aliphatic carbocation, (CH₃)₂CH-CH^+-CH₃ , which is stabilized by hyperconjugation ( 4 -hydrogens). 2. Halide (ii) forms a tertiary aliphatic carbocation, the 1 -methylcyclohexyl cation, which is stabilized by hyperconjugation ( 7 -hydrogens). 3. Halid