Question

Give plausible explanation for each of the following :

Why are amines less acidic than alcohols of comparable molecular masses?

Answer 1

Amines undergo protonation to give amide ion.

`R- NH_2 -> R - bar(N) H + H^(+)`

                         Amide ion

Similarly, alcohol loses a proton to give alkoxide ion.

`R - OH -> R - bar(O) + H^(+)`

Alcohol          Alkoxide ion

In an amide ion, the negative charge is on the N-atom whereas in alkoxide ion, the negative charge is on the O-atom. Since O is more electronegative than N, O can accommodate the negative charge more easily than N. As a result, the amide ion is less stable than the alkoxide ion. Hence, amines are less acidic than alcohols of comparable molecular masses

Answer 2

Loss of proton from an amine gives an amide ion while loss of a proton from alcohol give an alkoxide ion.

R—NH₂—>R—NH^– +H⁺

R—O —H—>R— O^– +H⁺ .

Since O is more electronegative than N, so it wijl attract positive species more strongly in comparison to N. Thus, RO~ is more stable than RNH®. Thus, alcohols are more acidic than amines. Conversely, amines are less acidic than alcohols.