Chapter 11, Problem 11.23P

Interpretation Introduction

Interpretation:

Alkenes A-D are to be ranked in order from the slowest to fastest rate of electrophilic addition of $\text{HCl}$.

Concept introduction:

Alkenes undergo electrophilic addition reactions when treated with a strong Bronsted acid. The reaction carried in two steps. In the first step, a pair of electrons from the electron-rich $\text{π}$ bond forms a bond to the acid’s electron-poor proton. This step generates a carbocation intermediate and a nucleophile, which is produced from the Bronsted acid. Step two is the coordination step in which the nucleophile produced is step one attacks the carbocation and forms a bond. The mechanism of the electrophilic addition involves the formation of carbocation, which is the rate-determining step. The reaction rate depends on how fast and easily the carbocation is formed. The more stable the carbocation is, the more stable the transition state and faster the reaction. The increasing order of carbocation stability is ${\text{1}}^{\text{0}}{\text{< 2}}^{\text{0}}{\text{< 3}}^{\text{0}}{\text{< 2}}^{\text{0}}{\text{benzylic < 3}}^{\text{0}}\text{benzylic}$. A carbocation is stabilized by the resonance effects. The alkene that forms the most stable carbocation will react the fastest in the electrophilic addition of a strong Bronsted acid.