Give explanation for each of the following :
(i) Why are amines less acidic than alcohols of comparable molecular masses ?
(ii). Why do primary amines have higher boiling points han tertiary amines ?
iii. Why are aliphatic amines stroner bases than aromatic amines ?

Explanation

(i) Loss of proton from amines give amide ion whereas loss of a proton from alcohol gives an alkoxide ion.
`underset("Amine")(RNH_(2)) to underset("Amide ion")(RNH^(-)) + H^(+)`
`underset("Alcohol")(ROH) to underset("Alkoxide ion")(RO^(-)) + H^(+)`
Since O is more electronegative than N, therefore, `RO^(-)` can accommodate the -ve charge more easily than `RNH^(-)`. Consequently, `RO^(-)` is more stable than `RNH^(-)`. Thus, alcohols are more acidic than amines.
(ii) Primary amines `(RNH_(2))` have two hydrogen atoms on the N atom and therefore, form intermolecular hydrogen bonding.
Tertiary amines `(R_(3)N)` donot have hydrogen atoms on the N atom and therefore, these donot form hydrogen bonds. As a result of hydrogen bonding in primary amines, they have higher boiling points than tertiary amines of comparable molecular mass. For example, b.p. of n-butylamine is 351 K while that of tert-butylamine is 319 K.
(iii) Both arylamines and alkylamines are basic in nature due to the presence of lone pair on N-atom. But arylamines are less basic than alkylamines. For example, aniline is less basic than ethylamine as shown by `K_(b)` values :
Ethylamine : `K_(b) = 4.7 xx 10^(-4)`
Aniline : `K_(b) = 4.2 xx 10^(-10)`
The less basic character of aniline can be explained on the basis of aromatic ring present in aniline. Aniline can have the following resonating structures :

It is clear from the above resonating structures that three of these (III, IV and V) acquire some positive charge on N atom. As a result, the pair of electrons become less available for protonation. Hence, aniline is less basic than ethyl amine in which there is no such resonance.