Ncert Exercises & Solutions

Which of the following haloalkanes reacts with aqueous KOH most

easily? Explain giving reason.

1. I-bromobutane
2. 2bromobutane

3. 2-bromo-2-methylpropane
4. 2-chlorobutane

2-bromo-2-methylpropane (ii), is a tertiary alkyl halicle and Here there is formation of most stable carbocation that is tertiary carbocation on hetrolytic cleavage of C-Br bond.

$B r C H_{3}$
$| |$
$H_{3} C — C — C H_{3} \to_{- B r^{-}}^{l o n i s a t i o n} H_{3} C — \overset{+}{C} — C H_{3} \overset{O H}{\to} C H_{3} — C — C H_{3}$
$| | |$
$C H_{3} C H_{3} O H$
$2 - b r o m o - 2 - m e t h y l p r o p a n e 3 ° c a r b o c a t i o n (s t a b l e) 2 - m e t h y l - 2 p r o p a n a l$

While as 4-bromobutane is primary alkyl halide and 2-bromobutane and 2-chlorobutane both are secondary alkyl halide So here There is a possibility of less stable carbocation formation.