Question

The correct increasing order of the reactivity of halides for $S_{N} 1$ reaction is:

• A. $CH _{3}- CH _{2}- X <\left( CH _{3}\right)_{2} CH - X < CH _{2}= CH - CH _{2}- X < PhCH _{2}- X $
• B. $\left( CH _{3}\right)_{2} CH - X < CH _{3}- CH _{2}- X < CH _{2} = CH - CH _{2} X < Ph CH _{2}- X $
• C. $PhCH _{2}- X <\left( CH _{3}\right)_{2} CH - X < CH _{3}- CH _{2}- X < CH _{2}= CH - CH _{2}- X$
• D. $ CH _{2}= CH - CH _{2}- X < Ph - CH _{2}- X <\left( CH _{3}\right)_{2} CH - X < CH _{3}- CH _{2}- X $

Answer 1

Answer: (A)

The relative stability of alkyl carbocation is due to inductive effect and hyperconjugation, while that of stable carbocation is due to resonance. The order is:
$CH _{3} CH _{2} X <\left( CH _{3}\right)_{2} CH - X< CH _{2}= CH - CH _{2} X < PhCH _{2}- X .$