(i) Amines undergo protonation to give amide ion.
`R-NH_(2) rarr underset("Amide ion")(R-overset(-)(N)H) +H^(+)`
Similary, alcohol loses a proton to give alkoxide ion.
`underset("Alcohol") (R-OH) rarr underset ("ion") underset("Alkoxide")(R- overset(-)(O))+H^(+)`
In an amide ion, the negative charge is on the BN-atom whereas in alkoxide ion, the negative charge is on the O-atom. Since O is more electronegative then N, O can accommodate the negative charge more easily than N. As a result, the amide ion is less stable than the alkoxde ion. Hence, amines are less acidic than alcohols of comparable molecular masses.
(ii) In a molecule of tertiary amine, there are no H- atoms whereas in primary amines, two hydrogen atoms are present. Due to the presence of H-atoms, primary amines undergo entexive intermolecular H- bonding.
As a result, extra energy is required to separate the molecules of primary amines. Hence, primary amines have higher boiling points than tertiary amines.
(iii) Due to the -R effect of the benzene ring, the electrons on the N-atom are less available in case of aromatic amines. Therefore, the electron on the N-atom in aromatic amines cannot be donated easily. This explains why aliphatic amines are stronger bases than aromatic amines.
