Question

Which of the following statements is correct for four isomeric bromobutanes?

• A. Of the two $1^{\circ}$ bromides, the carbocation intermediate derived from $\left( CH _{3}\right)_{2} CHCH _{2} Br$ is more stable than derived from $CH _{3} CH _{2} CH _{2} CH _{2} Br$
• B. The electron donating effect of $CH _{3} CH _{2} CH _{2} CH _{2}$-group is more than that of $\left( CH _{3}\right)_{2} CHCH _{2}-$ group
• C. $CH _{3} CH _{2} CH _{2} CH _{2} Br$ is more reactive than $\left( CH _{3}\right)_{2} CHCH _{2} Br$ in $S _{ N } 1$ reactions
• D. The decreasing order of $S_{N} 1$ reaction is $CH _{3} CH _{2} CH _{2} CH _{2} Br < \left( CH _{3}\right)_{2} CHCH _{2} Br < CH _{3} CH _{2} CH ( Br ) CH _{3}< \left( CH _{3}\right)_{3} CBr$

Answer 1

Answer: (A)

The electron donating effect of $CH _{3} CH _{2} CH _{2} CH _{2}$-group is less than that of $\left( CH _{3}\right)_{2} CHCH _{2}$-group.
$\left( CH _{3}\right)_{2} CHCH _{2} Br$ is more reactive than $CH _{3} CH _{2} CH _{2} CH _{2} Br$ towards $S _{ N }$ 1 reactions.
The decreasing order of $S _{ N } 1$ reaction is
$\left( CH _{3}\right)_{3} CBr > CH _{3} CH _{2} CH ( Br ) CH _{3}>\left( CH _{3}\right)_{2} CHCH _{2} Br > CH _{3} CH _{2} CH _{2} CH _{2} Br$
The given, order is the increasing order.