Nomenclature of Saturated Hydrocarbons

Nomenclature is a system of terms or rules that are used for forming these terms or names in a distinct field of science and arts. In simple terms it is an assignment of names to organic compounds. Saturated hydrocarbons are organic compounds that consist of carbon and hydrogen single bonds. In these compounds, there is the maximum number of hydrogen atom present for every carbon atoms. For example alkanes.

The saturated hydrocarbons are named according to the following rules:

Longest Chain Rule: The parent chain of the compound is considered the longest chain of carbon atoms.

Lowest Set of Locants: The numbering of the carbon atoms starts from the end which gives the lowest number to the carbon atom carrying the substituent.

Presence of Same Substituent More Than Once: Prefixes such as di, tri, etc are given to the substituents which are present twice, thrice respectively on the parent chain.

Naming Different Substituents: If more than one substituent is present then the substituents are arranged in their alphabetical order.

Naming Different Substituents At Equivalent Positions: If two different substituents are present in the same position from the two ends then the substituents are named so that the substituent which comes first in the alphabetical order gets the lowest number.

Naming The Complex Substituents: Naming of the complex substituent is done when the substituent on the parent chain has a branched structure (i.e complex structure). These substituents are named as a substituted alkyl group and the carbon atom of this substituent attached to the parent chain is numbered 1. The name of this type of substituent is written in brackets.

Let us understand it with the help of an example:

In this case, we have 9 carbon atoms in the straight chain. 5th Carbon atom from both the ends of the straight-chain, consists of substituents having 3 carbon chains. On the first two carbon atoms of the substituent group, there is one additional carbon atom attached.

Now if we consider this as a new parent chain, it has a substituent which has one additional carbon each. For naming them we will firstly number the parent chain. In this case, we have 9 carbon atoms in a straight chain which is also the parent chain. Then we find that the substituent is in the fifth position.

Now taking the substituent we will observe that we have 3 substituent carbons and out of these three, two substituents have additional carbons attached. We find that the longest chain in this can be the first four carbon atom chains but this is wrong as the last carbon is not attached to the parent chain.

So we will consider only three carbon atom chains as the main chain. Thus it can be named propane and in the first and second position, we have methyl group. We can write the name as 1-2 Dimethyl propane, but it will be written as 1-2 Dimethyl propyl as it is a substituent group.

Now taking the substituent with the parent chain we will get 5-(1-2-Dimethyl Propyl) and as the parent chain has 9 carbon atoms so, it will be named nonane. Thus, the final name of the compound will be 5-(1-2-Dimethyl Propyl)nonane.

Watch the video to understand the nomenclature of saturated hydrocarbons and get a deeper knowledge about the concept of nomenclature.