Topics in Organic Chemistry: Amines - Structure & Nomenclature

In this article we will learn about amine compound's structure and nomenclature.

Amines are considered as derivatives of ammonia where one or more hydrogen atoms are replaced by alkyl or aryl groups. In this article we will learn about IUPAC nomenclature of amines.

Key words: Amines, Derivatives of ammonia, Common nomenclature, IUPAC nomenclature.

Introduction

Amines are categorized as alkyl amines, aryl amines and heterocyclic amines. Amines are used as weak bases in organic synthesis.

Figure 1: Amines are derivatives of Ammonia

Amines are classified in to three subcategories,

Primary amines: In this type of amines one hydrogen atom of ammonia is replaced by alkyl or aryl group.

Secondary amines: Here the nitrogen atom is attached to two alkyl or aryl groups.

Tertiary amines: The tertiary amines consist of nitrogen atom which is bonded to three same or different substituents.

Primary amines

(One alkyl/ aryl group attached to nitrogen atom)

Secondary amines

(Two alkyl/ aryl group attached to nitrogen atom)

Tertiary amines

(Three alkyl/ aryl group attached to nitrogen atom)

Table 1: Classification of Amines

Quaternary ammonium salts is class compounds where a nitrogen atom is attached to four substituents. Ammonium salts has various industrial applications such as catalyst in phase transfer catalysis and making soaps.

Figure 2: Quaternary Ammonium Salts

Common Nomenclature

According to common naming system, amines are named by “alkyl” or “aryl” substituent followed by the word “amine”.

If two or three similar substituents are bonded to nitrogen atom, then prefixes like “di” for two and “tri” for three substituents are used for writing name of the amine.

If different substituents are bonded to nitrogen then they are written in alphabetical order.

Some examples of amine and their common names are shown in Table 2.

Compound	Name of alkyl/ aryl group	Prefix	Common name of amine
	Ethyl	-	Ethyl amine
	Isopropyl	-	Isopropyl amine
	Tert-butyl	-	Tert-butyl amine
	Benzyl	-	Benzyl amine
	Methyl	“di”	Dimethyl amine
	Ethyl	“tri”	Triethyl amine
	Butyl and ethyl	-	Butyl ethyl amine
	Ethyl and methyl	-	Ethyl methyl amine

Table 2: Common Names of Amines

IUPAC Nomenclature

Primary Amines

According to IUPAC naming system primary amines are named as derivatives of alkane. For example ethyl amine, here root name of the compound is “ethane” so the systematic name of compound is ethane + amine = ethanamine.

Figure: 3 IUPAC name of Ethyl amine

Similarly n-butyl amine can be named as butane + amine = butanamine.

Figure: 4 IUPAC name of Butyl amine

Table: 4 IUPAC names of Isomers of Hexyl amine

Secondary and Tertiary Amines

Names of secondary and tertiary amines are written in similar way like primary amine. Only difference is that N-alkyl / aryl substituent is added as prefix in the name of amine. For example diethyl amine is considered as derivative of ethanamine. So the systematic name is N-ethyl ethanamine.

Figure: 5 IUPAC name of diethylamine

If two different groups are bonded to nitrogen atom, then small alkyl group is considered as substituent. For example, ethyl propyl amine is viewed as derivative of propanamine and ethyl group is called as substituent. Therefore systematic name of the compound is N-ethyl propanamine.

Figure: 6 IUPAC name of ethyl propyl amine

The tertiary amines have three alkyl groups are bonded to nitrogen atom. In this case small groups are called as “substituents”. If substituents are similar then prefix “di” is used otherwise the substituents are written in alphabetical order.

For example, see the following compound which has three different groups bonded to nitrogen atom namely: isopropyl, methyl and butyl. Here isopropyl and methyl groups are small and butyl group is large. Therefore root name of the compound is “butanamine”. Other substituents should be written in alphabetical order. Hence full name of the compound is N-isopropyl N-methyl butan-1-amine.

Figure: 7 IUPAC name of butyl isopropyl methyl amine

For example tripropylamine has three propyl groups bonded to nitrogen atom. Here root name of the compound us “propan-1-amine”. There are two “propyl” groups bonded to nitrogen atom. Hence IUPAC name of the compound is “N,N-dipropyl-propan-1-amine”.

Figure: 8 IUPAC name of tripropylamine

Heterocyclic Amines

Heterocyclic amines are cyclic compound which consists of nitrogen atom in a ring. Some of the common nitrogen heterocyclic compounds are shown below.