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 an assignment of names to organic compounds. Saturated hydrocarbons are the organic compounds that consist of carbon and hydrogen single bond. In these compounds, there are the maximum number of hydrogen atom present for every carbon atom. For example Alkanes.

The saturated hydrocarbons are named according to the following rules:

Longest Chain Rule:The parent chain of the compound is considered as the longest chain of carbon atoms. This chain can either be straight or of any other shape.

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

Let us understand it with the help of an example:

Saturated Hydrocarbons

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 substituent 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 atom in a straight chain which is also the parent chain. Then we find that the substituent is on the fifth position.

Saturated Hydrocarbons

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

So we will consider only three carbon atom chain as the main chain. Thus it can be named as propane and on 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.

Saturated Hydrocarbons

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

Saturated Hydrocarbons

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

Practise This Question

Find total pressure observed after opening the stopcock .  [neglecting the volume of the tube connecting the two bulbs]