Question

In which of the following side chains (acyclic chain) is the main chain?
A.

B.

C.

D.

Answer 1

Hint :According to IUPAC nomenclature, in a compound the main chain is the longest chain of carbon atoms with maximum number of substituent groups is considered as the main chain and the alkyl groups attached to the main chain are known as side chains or substituent group.

Complete Step By Step Answer:
The most important factor to choose the main chain in an organic compound is the length of the chain. The main chain or parent chain must consist of the maximum number of carbon atoms and the second most important factor that affects is the number of substituents groups attached to the main chain. The parent chain or the main chain must consist of a maximum number of substituent groups. Hence, among given options:
In structure A:

The acyclic chain consists of three carbon atoms while the ring consists of five carbon atoms. Hence, the acyclic chain will not be the main chain for the given compound.
In structure B:

The acyclic chain consists of five carbon atoms which is equal to the number of carbon atoms in the ring. In this case, the priority is given to the ring or cyclic chains. Hence, the acyclic chain will not be the main chain for the given compound.
In structure C:

The acyclic chain consists of five carbon atoms which is equal to the number of carbon atoms in the ring but in this case the number of substituent groups on the acyclic chain are more than the ring or the cyclic chain. Hence, the acyclic chain will be the main chain for the given compound.
In structure D:

Both the acyclic chain consists of three carbon atoms whereas there are five carbon atoms in the cyclic chain. Hence, the acyclic chain will not be the main chain for the given compound.
Therefore, option (C) is the correct answer.

Note :
It is important to note that a functional group is always considered as a king in nomenclature of organic compounds i.e., if any functional group is present on the chain either cyclic or acyclic, then the chain consisting the functional group will always be considered as the parent chain or main chain.