Q. 144.7( 27 Votes )

Give plausible ex

Answer :

i) Amines undergo protonation to give amide ion.

 R-NH2 --> R-NH + H+

Similarly, alcohol loses a proton to give alkoxide ion.

 R-OH --> R-O + H+

In an amide ion, the negative charge is on the N-atom whereas, an 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.

ii) In a molecule of a 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 extensive 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 electrons on the N-atom in aromatic amines cannot be donated easily. This explains why aliphatic amines are stronger bases than aromatic amines.

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