Question

An organic compound $C_3H_5Cl\,(A)$ when treated with magnesium in diy ether gives $(B)$ which on treating with $CO_2$ followed by acid hydrolysis gives $C_4H_6O_2\, (C)$. $(C)$ is also obtained on oxidation of a hydrocarbon $(D)\, C_8H_{12}$. Structure of $A$ is

• A. $CH_2 = CH — CH_2 — Cl$
• B.
• C.
• D.

Answer 1

Answer: (D)

The reaction can be summerised as,

$\underset{(A)}{C _{3} H _{5} Cl + Mg} \xrightarrow{\text{ether}} (B) \xrightarrow[{(ii) H_2O/H^+}]{(i) CO_2}$

$\underset{(C)}{C _{4} H _{6} O _{2} }\xrightarrow{[ O ]} \underset{(D)}{C _{3} H _{12}}$

Let us consider any one of $a, b$ and $c$ options as $C _{3} H _{5} Cl$ and proceeds the reaction

$CH_2 =\underset{(A)}{CH-}CH_2-Cl \xrightarrow[{\text{ether}}]{Mg}CH_2-CH-CH_2-MgCl$



As it is known that carboxylic acid is also obtained on the oxidation of corresponding hydrocarbon.

$R- CH = CH -R \stackrel{[ O ]}{\longrightarrow } R COOH +R COOH$

Thus, by knowing the structure of $(C)$ as as $CH _{2}= CH - CH _{2}- COOH$, we can say that

structure of $C _{6} H _{12}$ will be

$CH _{2}= CH - CH _{2}- CH = CH - CH _{2}-CH = CH _{2}$

But this hydrocarbon on oxidation will not give acid (C) having molecular formula $C _{4} H _{6} O _{2}$ but it will give malonic acid, $CO _{2}$ and water.

$CH _{2}= CH - CH _{2}- CH = CH - CH _{2}$



Thus, among $a, b, c$ options none will give satisfactory explanation regarding the structure of hydrocarbon as they contain double bond hence, correct structure of $(A)$ will be cyclopropyl chloride.