Nomenclature of Amines

Have you ever wondered how things get their names? Well, we can’t decode all of it. But, we can certainly study about how various hydrocarbons get their names! Doesn’t that sound interesting? In this chapter, we will look at the nomenclature of Amines. First, we will take a quick revision of the definition of Amino group and classification of amines. Let’s begin.

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What are Amines?

Amines are one of the most important classes of organic compounds. We get them by replacing one or more hydrogen atoms by an alkyl or aryl group in a molecule of ammonia. They are commonly found in vitamins, proteins, hormones, etc. They are extensively used in the manufacturing of many drugs and detergents.

Classification of Amines

Depending upon the number of hydrogen atoms that can be replaced by an alkyl or aryl group in ammonia, amines are classified as primary (1^o), secondary (2^o) and tertiary (3^o).

If only one hydrogen atom is replaced then amines of the form R-NH₂ or primary amines (1^o) are obtained. In case, two of the three hydrogen atoms are replaced by alkyl/aryl groups then secondary amines are formed. When all the three hydrogen atoms are replaced by alkyl/aryl group then tertiary amines are obtained.

We have already seen this concept in the previous chapters. Now, that our memories are refreshed, let us move on to the next most important segment: the nomenclature of amines.

Nomenclature of Amines

In the branch of organic chemistry, the names of the compounds that are globally accepted are given according to the guidelines given by IUPAC for the nomenclature of organic compounds. Let us have a look at some of the rules for nomenclature of amines.

Rules of Nomenclature of Amines

• The naming of aliphatic amines is done by prefixing the alkyl group to the amines. Therefore, the names of aliphatic amines are of the form of an alkylamine. For example, CH₃NH₂ is named as methylamine (alkyl part + amine = methylamine).
• Prefixes such as di and tri are attached before the names of the alkyl group when two or more identical groups are present.
• If more than one amino group is present in the amine, a different rule is followed. Here, the parent chain and the position of amino groups is identified by numbering the carbon atoms in the parent chain. The numbering is done in such a way that the carbon atom bearing the –NH₂  groups get the lowest numbers.
• Prefixes along with the numbers are then used to denote the number of amino groups and their position in the molecule. For example, H₂N-CH₂-CH₂-NH₂  is named as ethane 1, 2-diamine.
• If –NH₂ group is attached to a benzene ring then it is called as arylamines.
• When we name arylamines according to the guidelines given by IUPAC then ‘e’ of the arene is replaced by the amine, for example, C₆H₅-NH₂ is named as benzenamine.

Solved Examples for You

Q1: Give an example of arylamine.

Ans: An example of arylamine is C₆H₅NH₂. It is commonly known as aniline which is also its IUPAC name.

Q2: The number of possible structures of amine (C₇H₉N) having one benzene ring is:

A) 5         B) 3        C) 4         D) 6

Solution: A) The five possible structures of  C₇H₉N are phenylemethanamine, N-methyl aniline, o-toluidine, m-toluidine, p-toluidine.