1,2-dihydroxybenzene (catechol) shows intramolecular H-bonding. So due to strong bonding, it should be difficult to break the bonds in 1,2-dihydroxybenzene and therefore, 1,2-dihydroxybenzene should have a higher boiling point than 1,3-dihydroxybenzene. Why is it not so?
Being more volatile implies that the molecules should be set free from mutual interactions. As 1,2-dihydroxybenzene has intramolecular H bonding, it is easy for it to exist independently, but for 1,3-dihydroxybenzene there might be intermolecular H bonding (interaction between two molecules); hence, it is a bit more difficult to break it apart, thus having a higher boiling point than its counterpart.