The amines can be regarded as compounds based on ammonia(NH₃) with one, two or three of the hydrogen atoms substituted by an alkyl or aryl group. Amines are classified into (a) Aliphatic amines and (b) Aromatic amines.

(a) Aliphatic amines are further classified into (i) primary amines (ii) secondary amines (iii) tertiary amines and (iv) cyclic amines.
(i) Primary amines arise when one of three hydrogen atoms in ammonia is replaced by an alkyl i.e., R–NH₂
Eg: Methylamine, Isopropylamine

(ii) Secondary amines have two alkyl substituents bound to ‘N’ together with one hydrogen i.e., R₂–NH
Eg: Dimethylamine or N–methylmethanamine, Ethyl methyl amine or N–methylethanamine

(iii) In tertiary amines, all three hydrogen atoms are replaced by organic substituents i.e., R₃–N
Eg: Trimethyl amine or N,N–dimethylmethanamine, Ethyl dimethyl amine or N,N–dimethylethanamine

(iv) Cyclic amines are either secondary or tertiary amines.
It is also possible to have four alkyl substituents on the nitrogen. These compounds are not amines but are called quaternary ammonium cations, have a charged nitrogen center and necessarily come with an anion.

(b) Aromatic amines have the nitrogen atom connected to an aromatic ring as in anilines.
Amines involve in hydrogen bonding, this have a significant influence in the properties of primary and secondary amines. Primary amines have more boiling points than secondary and tertiary. The lowering in boiling point is due to the lower dipole–dipole attractions and lower hydrogen bonding in secondary and tertiary amines. The boiling points of the primary amines increase with increase in chain length because of the greater amounts of van der Waals dispersion forces between the bigger molecules.

Aliphatic amines show some solubility in water. The solubility decreases with the increase in the number of atoms of carbon. The aromatic amines' (with nitrogen's lone pair electrons conjugated into the benzene ring) tendency to engage in hydrogen bonding is diminished. Thus boiling points are high and their solubility in water is low. Gaseous amines possess a characteristic "ammonia" smell and that of liquid amines have a distinctive “fishy” smell.

Structure and bonding:
In Ammonia the nitrogen, in addition to forming three sigma bonds, also carries an unshared electron pair. This means that there are four groups of electrons associated with the nitrogen. Mutual repulsion of these groups leads to a tetrahedral arrangement, much like that of a typical sp³ carbon atom. This predicts a bond angle between the N–H bonds of 109.5° which agrees pretty well with the observed value of 107° found in ammonia. Since the bonds connected to the nitrogen are shaped like a flattened pyramid, the arrangement is often called pyramidal. This ignores the unshared electron pair, whose inclusion leads to the tetrahedral description and the corresponding understanding of the nitrogen's hybridization as sp³.

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