Notes On Structure, Classification And Nomenclature - CBSE Class 12 Chemistry

Alkyl (or) aryl derivatives of ammonia are known as amines.

Amines formed by the replacement of one (or) more hydrogen atoms of an ammonia molecule by alkyl groups are called alkyl amines and those formed by the replacement of the hydrogen by aryl groups are called aryl amines.

The Nitrogen atom in amines is sp3 hybridised. Out of the four sp3 hybrid orbitals, three overlap with the orbitals of either the hydrogen or the carbon. The fourth sp3 hybrid orbital contains an unshared pair of electrons. Hence, amines posses pyramidal geometry.

Due to the presence of an unshared pair of electrons, the C-N-H (or) C-N-C bond angle is less than the normal tetrahedral bond angle of 109.5°.

Depending upon the number of hydrogen atoms replaced by alkyl (or) aryl groups in the ammonia molecule, amines are classified into three types.

The replacement of one, two and three hydrogen atoms of ammonia with one, two and three alkyl (or) aryl groups yields primary, secondary and tertiary amines.

Amines are called simple amines when all the alkyl (or) aryl groups are the same and mixed amines when they are different.

In the common system an aliphatic amine is named by prefixing the alkyl group to the amine.

In the IUPAC system, alkylamines are named alkanamines.

Ex:

While naming arylamines according to the IUPAC system, the suffix 'e' of the arene is replaced by 'amine'.

Summary

Alkyl (or) aryl derivatives of ammonia are known as amines.

Amines formed by the replacement of one (or) more hydrogen atoms of an ammonia molecule by alkyl groups are called alkyl amines and those formed by the replacement of the hydrogen by aryl groups are called aryl amines.

The Nitrogen atom in amines is sp3 hybridised. Out of the four sp3 hybrid orbitals, three overlap with the orbitals of either the hydrogen or the carbon. The fourth sp3 hybrid orbital contains an unshared pair of electrons. Hence, amines posses pyramidal geometry.

Due to the presence of an unshared pair of electrons, the C-N-H (or) C-N-C bond angle is less than the normal tetrahedral bond angle of 109.5°.

Depending upon the number of hydrogen atoms replaced by alkyl (or) aryl groups in the ammonia molecule, amines are classified into three types.

The replacement of one, two and three hydrogen atoms of ammonia with one, two and three alkyl (or) aryl groups yields primary, secondary and tertiary amines.

Amines are called simple amines when all the alkyl (or) aryl groups are the same and mixed amines when they are different.

In the common system an aliphatic amine is named by prefixing the alkyl group to the amine.

In the IUPAC system, alkylamines are named alkanamines.

Ex:

While naming arylamines according to the IUPAC system, the suffix 'e' of the arene is replaced by 'amine'.

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