question_answer 23)

Give plausible explanation for each of the following : (i) Why are amines less acidic than alcohols of comparable molecularmasses? (ii) Why do primary amines have higher boiling point than tertian-amines? (iii) Why are aliphatic amines stronger bases than aromatic amines?   (i) Consider polarity of  and bonds, (ii) More is the ease of H?bond formation, higheris the boiling point. (iii) Resonance and proton at ion in case of aromatic amines,  

Answer:

(i) Amines are less acidic than alcohols of comparable molecular masses because  bond is less polar than  bond. Hence, amines release  ion with more difficultly ascompared to alcohol. (ii) Intermolecular hydrogen bonding is present in primary amines but not in tertiary amines (H-atom absent, in amino group) soprimary amines have higher boiling point than tertiary amines. (iii) Aliphatic amines are stronger bases than aromatic amines due to following reasons: (a) Electron pair on the nitrogen atom of aromatic amines is involved in conjugation with the electron pairs of the ring as follows     (b) Anilinium ion obtained by accepting a proton is less stabilized by resonance.     So, aniline is a weaker base than alkyl amines, in which  effectincreases the electron density on the nitrogen atom.