Why `2^@` amine is more basic than `1^@` and `3^@` amine ?

Explanation

Basic character of `1^(@), 2^(@) and 3^(@)` amines in aqueous solutions depend upon following two factors on the basis of electron donating effect of alkyl group :
1. On the basis of electron donating effect of alkyl group, the basic character of `1^(@), 2^(@)and3^(@)` amines should be in the order,

2. On the basis of H-bonding : Amines dissolve in water and ionise to give `OH^(-)` ions, which are responsible for their basic character in aqueous solutions. For example `1^(@)` amine dissolve in water and ionise as follows :
`underset(1^(@)"Amine")(R-oversetoverset(H)(|)underset(..)(N)-H)+H_(2)Orarr[R-underset(H)underset(|)overset(H)overset(|)NH]^(+ -)OHiffunderset("Intermadiate")([R-undersetunderset(H)(|)oversetoverset(H)(|)N-H]^(+))+OH^(-)`
The stability of the carbon so formed depends upon the extent of H-bonding. More the number of H-atoms bonded to N-atom, more is the H-bonding and hence more is the stability. A high stability of carbon means a more basic character. This make `1^(@)` amines most basic. Thus on the basis of H-bonding the basic character of amines should be in the order.
`3lt2^(@)lt1^(@)`
Combined effect of there two factors makes `2^(@)` amine more basic than `1^(@) and 3^(@)` amines.