COMEDK2025ChemistryHaloalkanes and HaloarenesActual
Arrange the following compounds in the increasing order towards S _ N 1 reactions.
Options
- AIV < II < I < III
- BI < III < II < IV
- CIV < III < II < I
- DI < II < III < IV
Correct answer
B. I < III < II < IV
Step-by-step solution
The rate of an S_ N 1 reaction depends on the stability of the carbocation intermediate formed after the departure of the leaving group (bromide ion). The more stable the carbocation, the faster the S_ N 1 reaction. The carbocations formed from the given compounds are: (I) Benzyl carbocation: C₆H₅CH₂⁺ , which is stabilized by resonance with one phenyl ring. (II) Diphenylmethyl carbocation: (C₆H₅)₂CH⁺ , which is stabilized by resonance with two phenyl rings. (III) 1-Phenylethyl carbocation: C₆H₅CH(CH₃)⁺ , which is s