1. CH3NH2 is a small, polar molecule and can hydrogen bond with water.
CH3(CH2)5 CH2NH2 can also hydrogen bond with water via the amino group but is much less polar due to the presence of a much longer, non-polar, hydrocarbon chain.
2. CH3CHO is small and polar, and can hydrogen bond with water via the O on the C=O group. HOCH2CHO is also small and polar but, in addition to hydrogen bonding with water via the O on the C=O group, can also hydrogen bond with water via the -OH group.
3. Compounds containing the large, non-polar, benzene rings tend not to be very soluble in water.
Alcohols and amines can both form hydrogen bonds with water, but in alcohols the hydrogen bonding is stronger.