State reasons for the following : (i) pK_(b) value for aniline is more than that for methylamine. (ii) Ethylamine is soluble in water whereas aniline is not soluble in water. (iii) Primary amines have higher boiling points than tertiary amines.

State reasons for the following : (i) pK_(b) value for aniline is mor

1.	State reasons for the following : (i) pK_(b) value for aniline is more than that for methylamine. (ii) Ethylamine is soluble in water whereas aniline is not soluble in water. (iii) Primary amines have higher boiling points than tertiary amines.
Answer» SOLUTION :(i) Electron density on N in ANILINE decreases due to RESONANCE with benzene ring whereas electron density on N in methylamine increases due to inductive effect of `-CH_(3)` group. Thus, methylamine is more basic than aniline. In other words `K_(b)` for methylamine is higher. Since, `pK_(b)` is equal to `-log K_(b)`, it is more for aniline than for methylamine. (ii) Ethylamine forms a hydrogen bond with water. But hydrogen bond formation tendency decreases as the alkyl/aryl part increases in size because it is hydrophobic in nature. Hence, due to big phenyl group, aniline is not soluble in water. (iii) Primary amines are able to form intermolecular hydrogen BONDS among their molecules, leading to association of molecules. This raises the b.p. of primary amines. There being no hydrogen attached to N in tertiary amines, there is no POSSIBILITY of hydrogen bonding. Hence, tertiary amines have lower boiling points or primary amines have higher boiling points.