Question

$C_3H_9N$ cannot represent:
A.${1^0}$ amine
B.${2^0}$ amine
C.${3^0}$ amine
D.quaternary salt

Answer 1

We have the compound with the molecular formula ${C_3}{H_9}N$. We can use the basics of isomers here. Make the isomers of a compound with the molecular formula ${C_3}{H_9}N$. Then classify them as primary, secondary, and tertiary amines.

Complete step by step answer:
We will try to draw some isomers of a compound with the molecular formula ${C_3}{H_9}N$. We will consider and understand all the options one by one. So let’s start.
We can write the structure of the compound with molecular formula ${C_3}{H_9}N$ as,

The above structure is a primary ${1^0}$ amine. As the nitrogen atom is surrounded by a single carbon or chain. So we can represent ${C_3}{H_9}N$ as ${1^0}$ amine.
Now consider another structure with the molecular formula ${C_3}{H_9}N$ which is represented as,

The above structure is ${2^0}$ amine. Here the nitrogen atom is surrounded by two carbon atoms. So we can represent ${C_3}{H_9}N$ as ${2^0}$ amine.
Now we will consider another structural isomer of molecular formula ${C_3}{H_9}N$ which is represented as,

The above structure is a ${3^0}$ amine. In the structure, we can observe that the nitrogen atom is surrounded by three carbon atoms therefore it is termed as ${3^0}$ amine. So we can represent ${C_3}{H_9}N$ as ${3^0}$ amine.
Now the last option is quaternary salt. This salt is represented as ${R_4}\mathop N\limits^ + \mathop Z\limits^ -$ where ${R_4}$ represents the alkyl group with $4$ carbon atoms. But in the compound with the molecular formula, ${C_3}{H_9}N$ we have $3$ carbon atoms. So we cannot represent ${C_3}{H_9}N$ it as quaternary salt.

Therefore, the correct option is (D).

Note:
${R_4}\mathop N\limits^ + \mathop Z\limits^ -$ is the quaternary ammonium halide. It is formed when ammonia accepts one proton to form an ammonium ion and the tertiary amine accepts an alkyl group to form a quaternary ammonium ion.
Primary, secondary and tertiary amines are represented as ${1^0},{2^0},{3^0}$ amine respectively.