Question

Give the IUPAC name of the chain isomer of butane.
A. $2 - methyl - 1 - butene$
B. $2 - methyl - 2 - butene$
C. $2 - methylpropane$
D. $2,2 - dimethylpropane$

Answer 1

We know that the molecules which have the same molecular formula but differ by the atoms or bonds are called a structural isomer. It is also known as a constitutional isomer. It is divided into two types (1) chain isomers and (2) ring isomers.

Complete step by step answer:

We must remember chain isomers of alkanes have the same molecular formula but different arrangement of carbon skeleton.
First, we see the structure of butane and its chain isomer,

Consider the molecules in A and B. The molecular formula of both the compounds is ${C_4}{H_{10}}$ but molecule A is linear while molecule B is branched. Thus molecule B is a chain isomer of butane. The longest chain has 3 C atoms and one methyl substituent and the common name of chain isomer of butane is isobutane. The IUPAC name of the compound is $2 - methylpropane$.
So, the correct answer is “Option C”.

Additional Information: We know that the molecules which have the same molecular formula but different molecular geometries are called isomers. There are several types of isomers. They are,
-Conformational isomers.
-Constitutional isomers.
-Stereoisomers.
Now we can discuss about the types of isomer as,
-Ring isomer:
The isomers which are having the same molecular formula but they have a different structural formula to the type of ring are called ring isomers.
-Stereoisomers:
The isomers which differ by the orientation of atoms in space are called stereoisomers. Stereoisomers are of two types: (1) Geometrical isomer and (2) optical isomer.
-Conformational isomer:
Conformational isomers are the isomers that are differing by their rotation around a single bond.

Note: We must remember that the parent chain of isobutane is propane and the methyl group is attached to the second carbon of the chain thus, its IUPAC name is $2 - methylpropane$.