Question

Structures of molecules of two compounds are given below :

(I)	(II)

1. Which of the two compounds will have intermolecular hydrogen bonding and which compound is expected to show intramolecular hydrogen bonding.
2. The melting point of a compound depends on, among other things, the extent of hydrogen bonding. On this basis explain which of the above two compounds will show higher melting point.
3. Solubility of compounds in water depends on power to form hydrogen bonds with water. Which of the above compounds will form hydrogen bond with water easily and be more soluble in it.

Answer 1

(a) Compound I will form intramolecular hydrogen bond because \[\ce{NO2}\] and \[\ce{OH}\] groups are close together whereas it is not so in compound II. Compound II will have intermolecular hydrogen bonding. Bonding in both the cases is shown below:

(I)	(II)

(b) As a large number of molecules can be linked together through intermo­lecular hydrogen bonding, compound II will show higher melting point.

(c) Due to intramolecular hydrogen bonding, compound I will not be able to form hydrogen bonds with \[\ce{H2O}\] molecules. Hence, it will be less soluble in water. However, compound II can form hydrogen bonds with \[\ce{H2O}\] molecules easily and hence it will be more soluble in water.