Example 9.5

Example . Amines can be considered as derivatives of ammonia obtained by replacement of hydrogen atoms with alkyl or aryl groups. Replacement of one hydrogen atom of ammonia gives rise to structure of the type R-NH , known as primary amine . Secondary amines are characterised by the structure R NH or R-NHR ¢¢¢¢¢ and tertiary amines by R N, RNR ¢¢¢¢¢ R ¢¢¢¢¢¢¢¢¢¢ or R NR ¢.¢.¢.¢.¢. Secondary and tertiary amines are known as simple amines if the alkyl or aryl groups are the same and mixed amines if the groups are different. Like ammonia, all the three types of amines have one unshared electron pair on nitrogen atom due to which they behave as Lewis bases . Amines are usually formed from nitro compounds, halides, amides, imides, etc. They exhibit hydrogen bonding which influence their physical properties. In alkylamines , a combination of electron releasing, steric and H-bonding factors influence the stability of the substituted ammonium cations in protic polar solvents and thus affect the basic nature of amines. Alkyl amines are found to be stronger bases than ammonia. In aromatic amines , electron releasing and withdrawing groups, respectively increase and decrease their basic character. Aniline is a weaker base