Question

The correct order of reactivity of the three halides ethyl chloride (I), iso-propyl chloride (II) and benzyl chloride (III) in $S_{N}1$ reaction is

• A. I>II>III
• B. III>II>I
• C. II>I>III
• D. I>III>II

Answer 1

Answer: (B)

For $S_{N}1$ reactions, greater the stability of carbocations faster will be the rate of reaction. Due to greater stabilisation of benzylic carbocation intermediate by resonance, it shows higher reactivity in $S_{N}1$ reactions than other aliphatic halides. Since, the order of reactivity of halides -is benzyl chloride > iso-propyl chloride > ethyl chloride.