Question

An alkyl chloride $(A)$ on reaction with magnesium in dry ether followed by treatment with ethanol gave $2$-methylbutane. Give the possible structure of $A$

• A. $\left( CH _{3}\right)_{2} C ( Cl ) CH _{2} CH _{3}$
• B. $\left( CH _{3}\right)_{2} CHCH _{2} CH _{2} Cl$
• C. $CH _{3} CH _{2} CH _{2} CH _{2} CH _{2} X$
• D. Both (a) and (b)

Answer 1

Answer: (D)

Since, the compound gives 2-methyl butane, it must contain the following carbon skeleton.
$C-\overset{\underset{|}{C}}{C}-C-C$
Thus, the structure of chloride may be
$\left( CH _{3}\right)_{2} C ( Cl ) CH _{2} CH _{3}$
or $\left( CH _{3}\right)_{2} CHCH _{2} CH _{2} Cl$ and the reactions are as follows
$\left( CH _{3}\right)_{2} C ( Cl ) CH _{2} CH _{3}+ Mg \xrightarrow{\text { dry ether }}$
$\left( CH _{3}\right)_{2} \underset{\overset{|}{C}}{M}gCl - CH _{2} CH _{3} \xrightarrow{ C _{2} H _{5} OH } (CH_3)_2CHCH_2CH_3$
$\left( CH _{3}\right)_{2} CHCH _{2} CH _{2} Cl + Mg \xrightarrow{\text { dry ether }}$
$\left( CH _{3}\right)_{2} CHCH _{2} CH _{2} MgCl \xrightarrow{ C _{2} H _{5} OH }(CH_3)_2CHCH_2CH_3$