At normal temperature o-hydroxybenzaldehyde is a liquid but p-hydroxybenzaldehyde is a solid. Give reason.

Explanation

In o-hydroxybenzaldehyde, the -OH and -CHO groups are situated at the two adjacent C-atoms of the benzene ring and are involved in intramolecular hydrogen bonding. These molecules exist as discrete molecules and have a lower melting point. On the other hand, in p-hydroxybenzaldehyde, the -OH and -CHO groups are situated away from each other. hence, intermolecular hydrogen bonding does not exist. there molecules remain associated through intermolecular hydrogen bonding and hence have a high melting point. thus the ortho-isomer exists as a liquid while the para-isomer exists as a solid.
ltBrgt Interamolecular H-bond in o-hydroxybenzaldehyde.

Intermolecular H-bond in p-hydroxy benzaldehyde.