Common Names Of Alkanes

As I have explained in my earlier blog about Alkanes and its IUPAC names, common names of alkanes are also as equally important as IUPAC names.

So what is actually the difference between a common name and IUPAC name?

Common names are nothing but the simplest name yet confusing names given to compounds having complex structures.

Luckily common names of alkanes are not that complex because they contain less number of carbon atoms.

To understand easily I generally prefer to give my students two rules for understanding this, which are as follows,

1. Count the total number of carbon atoms present in the molecule irrespective of whether it is straight chain or branched chain.

2. Look for the specific branch in the structure which will help you to use the suitable prefixes such as n-, iso-, neo-, tert- and sec- prefixes.

What are these prefixes and how to understand them easily?

• n- stands for normal chain which can be used when alkanes are straight chains. The important point to note here is n- prefix is used only in presence of more than three carbons. We can easily understand with the following example.

            

As this is a straight chain compound and contains four carbon in a straight chain hence the name will be n-butane.

   

As this compound contains three carbon and only one possible structure we can draw from any side hence no prefix can be used for this and a simple common name will be propane.

• iso- it is used when there is presence of a methyl group on 2nd  carbon in the molecule. For example

          

          

As there is presence of a methyl group on the 2nd  and total carbon atoms present are five hence the common name of the compound is iso-butane.

• neo- it is used when there is presence of  two methyl groups on 2nd  carbon in the molecule.

For example

As there is presence of two methyl groups on the 2nd  and total carbon atoms present are six, hence the common name of the compound is neo-butane.

• tert- and sec- prefixes are used only when there is presence of a functional group in the compounds. This we will discuss in my upcoming blogs.

Here are some example for you to understand the common names of alkanes

n-hexane

iso-heptane

neo-octane

One of the unique example of common name is 

In this example there are two methyl groups present on 3rd carbons hence we can not use iso or neo prefixes to write the common names hence the name of this compound is nonane only.

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