Question

Give plausible 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 poings han tertiary amines ?
iii. Why are aliphatic amines stroner bases than aromatic amines ?

Answer 1

i. The loss of a proton from an amine give an imide ion. While the loss of a proton from alcohol gives an alkoxide ion as shown below :
`underset("Amine")(R-NH_(2)) rarr underset("Imide ion")(R-overset(Theta)NH)+H^(o+)`
`R-O-H rarr R-O^(Theta) +H^(o+)`
Since `O` is more elecronegative than `N`, therefore, `(Roverset(Theta)O)`can accommodate the negative charge more easily than `Roverset(Theta)NH` can accommodate the negative charge. In other words, `RO^(Theta)` is more stable than `Roverset(Theta)NH`. Thus, alcohols are more acidic than amines. Conversely, amines are less acidic than alcohols.
ii. `1^(@)` amines form stronger intermolecular H-bonding between N atom of one and H atom of another molecule.
iii. Aliphatic amines are stronger bases due to `+I` effect of the alkyl group, leading to high `bar(e)` density on the N atom.