Introduction, nomenclature and classification of aliphatic amines

Introduction of aliphatic amines

Amines may be regarded as the alkyl or aryl derivatives of ammonia. They are obtained by the replacements of one or more hydrogen atoms of ammonia by alkyl or aryl groups. They can be classified into primary, secondary or tertiary amines depending upon whether two or three H atoms of ammonia have been replaced by alkyl or aryl groups.

Thus the characteristic functional groups for primary, secondary and tertiary amines are:

There is yet another class of compound, besides these three types of amines, in which N atom is quaternary. Such compounds are called quaternary ammonium salts. They are regarded as derivatives of ammonium salt in which all the four H atoms are replaced by alkyl or aryl groups.

Example:

Nomenclature of aliphatic amines

Aliphatic amines are named by adding the suffix amine to the name of the alkyl group and it is written as one word. E.g., C₂H₅NH₂ is Ethylamine. When two or more alkyl groups in secondary or tertiary amines are some, the prefix di or tri is used. For e.g., (C₂H₅)₂ NH is diethylamine.

In the case of mixed amines, the names of alkyl groups are arranged in alphabetical order. The amines are named as N-substituted derivatives of the largest group of primary amine.

Example:

(C₂H₅)₂NCH₂CH₂CH₂CH₃ - N, N - diethyl butylamine

In the IUPAC system the amines are considered to be amino derivatives of corresponding alkanes. Therefore, they are called aminoalkanes or alkanamines. These names are obtained either by adding a prefix amino before the name of parent alkane or by replacing 'e' from the name of the parent alkene with suffix amine.

Examples:

In case of diamines the ending e of the hydrocarbon name is retained and the suffix diamine is added H₂N-(CH₂)₅-NH₂ is 1,5 - Pentanediamine.

When additional functional groups such as -OH or double bond are present in an amine, the prevailing priority order for nomenclature is observed.

H₂N CH₂ CH₂ OH 2 - amino ethanol

H₂N CH₂ CH = CH₂ is 2 - propen1 - amine

Structure of aliphatic amines

Aliphatic amines have a pyramidal shape that is approximately tetrahedral when we assume the electron pair on nitrogen as a group. An amine which has 3 different groups attached to nitrogen has chiral nitrogen. But such amines cannot be resolved into enantiomers because of rapid inversion of an enantiomer to its mirror image.

In aromatic amines, because the electron pair of nitrogen can conjugate with the benzene ring giving carbon nitrogen bond with double bond character. This is why the C - N bond in aromatic amines is shorter than in aliphatic amines.