Question

Assertion: ${{C}_{2}}{{H}_{5}}Br$ reacts with alcoholic solution of $AgN{{O}_{2}}$ to form nitroethane as the major product.
Reason: $NO_{2}^{-}$ is an ambient ion.
(a) Both assertion and reason are correct and reason is the correct explanation for assertion.
(b) Both assertion and reason are correct but reason is not the correct explanation for assertion.
(c) assertion is correct but reason is incorrect.

Answer 1

Hint: By ambident we mean that it consists of two atoms through which it can attack the alkyl halide and in case of covalent compounds, attack occurs always through the nitrogen attack and results in the formation of nitroethane. Now answer it.

Complete answer:
First of all, let’s discuss ethyl bromide. Ethyl bromide is an alkyl halide i.e. haloalkane and is formed by the action of the halogens on alkanes. When this ethyl bromide is made to react with the ammonia solution of the silver nitrite, it results in the formation of nitroethane. It is so because; Nitrite ion is an ambident nucleophile i.e. it means that there are two sites i.e. the oxygen and the nitrogen through which it can attack the alkyl halide. Attack through the nitrogen gives nitro compounds and attack through the oxygen gives nitrites.
In case of silver nitrite, being a covalent compound, the bond between the Ag-O is covalent and therefore, it does not have a negative charge on the oxygen atom. Hence the nucleophilic attack occurs through the lone pair on nitrogen forming nitroalkanes. The reaction occurs as;
${{C}_{2}}{{H}_{5}}Br+AgN{{O}_{2}}\to {{C}_{2}}{{H}_{5}}N{{O}_{2}}+AgBr$
So, it concludes that both the assertion and reason are correct but reason is not the correct explanation for the assertion.

Hence, option (b) is correct.

Note: When the nitrite ion reacts with alkali metal nitrites, the bond between the K-O is ionic as alkali metal nitrites are ionic compounds , then the negative charge on the oxygen is the attacking site and it results in the formation of alkyl nitrites.