Arrange in increasing order of basic strength giving reason: C2H5NH2, C6H5NH2,(C2H5)2NH
The basicity of amines should decrease in the order:
3° amine > 2° amine >1° amine > NH3 > Aniline
The reason is simple : The electron releasing substituent increases the basicity.In aniline(C6H5NH2) the lone pair of nitrogen is shared with benzene ring .So the aniline is least basic in all.But there is variation found in primary secondary and tertiary amine in presence of water.
It is found that in aqueous solution, 2° amine is more basic than 1° and 3° amine.
The basicity of an amine in aqueous solution depends upon the stability of the ammonium cation, which in turn depends upon a combination of the following three factors:
(1) +I effect of the alkyl group
(2) Extent of hydrogen bonding with water molecules.
(3) Steric effect of the alkyl groups
According to steric effect, the crowding of alkyl groups around N- atom, hinders the attack of proton on the amine molecule and this decreases its basic strength. Since crowding of alkyl groups around N atom increases from primary to tertiary amines, so the basic strength of amine should decrease in the order 1 degree > 2 degree > 3 degree .
But, hydration due to hydrogen-bonding is maximum in monoalkyl ammonium ion (protonated cation of primary amine), it is less in dialkyl ammonia ion and still less in trialkyl ammonium ion. Thus basic strength should decrease from 1 degree > 2 degree > 3 degree.
Since inductive effect also plays its role and according to that the basicity trend is 3° amine > 2° amine >1° amine.
But summing of all 3 factors it is found that the basicity order in aqueous solution follow the trend
Secondary > Tertiary > Primary
In aqueous phase:
(C2H5)2NH > (C2H5)3N > C2H5NH2 > C6H5NH2.
The basicity of amines should decrease in the order:
3° amine > 2° amine >1° amine > NH3 > Aniline
The reason is simple : The electron releasing substituent increases the basicity.In aniline(C6H5NH2) the lone pair of nitrogen is shared with benzene ring .So the aniline is least basic in all.But there is variation found in primary secondary and tertiary amine in presence of water.
It is found that in aqueous solution, 2° amine is more basic than 1° and 3° amine.
The basicity of an amine in aqueous solution depends upon the stability of the ammonium cation, which in turn depends upon a combination of the following three factors:
(1) +I effect of the alkyl group
(2) Extent of hydrogen bonding with water molecules.
(3) Steric effect of the alkyl groups
According to steric effect, the crowding of alkyl groups around N- atom, hinders the attack of proton on the amine molecule and this decreases its basic strength. Since crowding of alkyl groups around N atom increases from primary to tertiary amines, so the basic strength of amine should decrease in the order 1 degree > 2 degree > 3 degree .
But, hydration due to hydrogen-bonding is maximum in monoalkyl ammonium ion (protonated cation of primary amine), it is less in dialkyl ammonia ion and still less in trialkyl ammonium ion. Thus basic strength should decrease from 1 degree > 2 degree > 3 degree.
Since inductive effect also plays its role and according to that the basicity trend is 3° amine > 2° amine >1° amine.
But summing of all 3 factors it is found that the basicity order in aqueous solution follow the trend
Secondary > Tertiary > Primary
In aqueous phase:
(C2H5)2NH > (C2H5)3N > C2H5NH2 > C6H5NH2.
