Question

A compound X on ozonolysis forms two molecules of $HCHO$. Compound X is
A. ${{C}_{2}}{{H}_{4}}$
B. ${{C}_{2}}{{H}_{2}}$
C. ${{C}_{2}}{{H}_{6}}$
D. ${{C}_{6}}{{H}_{6}}$

Answer 1

Hint: The ozonolysis of alkenes is a process of oxidatively cleaving alkenes or alkynes using ozone, ${{O}_{3}}$. By this method, carbon-carbon double bonds or triple bonds are replaced by double bonds with oxygen. Here we have to check whether the given substrates are alkenes or alkynes to form two molecules of formaldehyde, $HCHO$.

Complete Step by Step Answer:
Ozonolysis is a process in which ozone cleaves the unsaturated bonds of alkenes, alkynes, or azo compounds. Thereby cleaving the double bonded oxygen of alkene and alkynes produce carbonyl compounds whereas azo compounds produce nitrosamines. Through this oxidizing method alcohols, ketones, aldehydes as well as carboxylic acids can be formed as a product.
The intermediate ozonide further converts to a carbonyl derivative after completion of the workup. This work may be reductive or oxidative. Carboxylic acids are produced by oxidative work up and aldehydes or ketones are formed by a reductive workup.
The general formula of alkanes, alkenes, and alkynes are${{C}_{n}}{{H}_{2n+2}}$, ${{C}_{n}}{{H}_{2n}}$and ${{C}_{n}}{{H}_{2n-2}}$respectively. Here $n$are the number of carbon atoms.
From (A), the compound is alkene, ethylene (where $n=2$)undergoes ozonolysis to give two molecules $HCHO$.

But an alkyne, acetylene from (B) undergoes ozonolysis and reacts with ozone to produce glyoxal.

From (C) it is an alkane compound, ethane does not undergo ozonolysis due to the stable sigma bond present in ethane.
Benzene ${{C}_{6}}{{H}_{6}}$reacts with ozone to form three molecules of glyoxal.

Therefore compound X is ethylene, ${{C}_{2}}{{H}_{4}}$.
Thus, option (A) is correct.

Note: Ozonolysis, is a method in organic chemistry to determine the position of a carbon-carbon double bond $(C=C)$ in any unsaturated compound. This process has been used widely in the determination of the structures of natural products, for the synthesis of rare carbonyl compounds, etc.