Giveplausible explanation for each of the following:
(i) Why are amines less acidic thanalcohols of comparable molecular masses?
(ii) Why do primary amines have higherboiling point than tertiary amines?
(iii) Why are aliphatic amines strongerbases than aromatic amines?
Giveplausible explanation for each of the following:
(i) Why are amines less acidic thanalcohols of comparable molecular masses?
(ii) Why do primary amines have higherboiling point than tertiary amines?
(iii) Why are aliphatic amines strongerbases than aromatic amines?
(i) Aminesundergo protonation to give amide ion.
Similarly,alcohol loses a proton to give alkoxide ion.
Inan amide ion, the negative charge is on the N-atom whereas inalkoxide ion, the negative charge is on the O-atom. Since O is moreelectronegative than N, O can accommodate the negative charge moreeasily than N. As a result, the amide ion is less stable than thealkoxide ion. Hence, amines are less acidic than alcohols ofcomparable molecular masses.
(ii) In a molecule of tertiary amine, there are no H−atomswhereas in primary amines, two hydrogen atoms are present. Due to thepresence of H−atoms, primary amines undergo extensiveintermolecular H−bonding.
Asa result, extra energy is required to separate the molecules ofprimary amines. Hence, primary amines have higher boiling points thantertiary amines.
(iii) Due to the −R effect of the benzene ring, theelectrons on the N- atom are less available in case of aromaticamines. Therefore, the electrons on the N-atom in aromatic aminescannot be donated easily. This explains why aliphatic amines arestronger bases than aromatic amines.
(i) Aminesundergo protonation to give amide ion.
Similarly,alcohol loses a proton to give alkoxide ion.
Inan amide ion, the negative charge is on the N-atom whereas inalkoxide ion, the negative charge is on the O-atom. Since O is moreelectronegative than N, O can accommodate the negative charge moreeasily than N. As a result, the amide ion is less stable than thealkoxide ion. Hence, amines are less acidic than alcohols ofcomparable molecular masses.
(ii) In a molecule of tertiary amine, there are no H−atomswhereas in primary amines, two hydrogen atoms are present. Due to thepresence of H−atoms, primary amines undergo extensiveintermolecular H−bonding.
Asa result, extra energy is required to separate the molecules ofprimary amines. Hence, primary amines have higher boiling points thantertiary amines.
(iii) Due to the −R effect of the benzene ring, theelectrons on the N- atom are less available in case of aromaticamines. Therefore, the electrons on the N-atom in aromatic aminescannot be donated easily. This explains why aliphatic amines arestronger bases than aromatic amines.
