Due to intramolecular H – bonding orthohydroxy benzaldehyde exists as discrete molecule whereas due to intermolecular H – bonding, p – hydroxybenzaldehyde exists as associated molecules. To break these intermolecular H – bonds, a large amount of energy is needed.
Consequently, p – hydroxybenzaldehyde has a much higher m.pt. and b.pt. than that of o – hydroxy benzaldehyde. As a result, o -hydroxy benzaldehyde is a liquid at room temperature while p – hydroxy benzaldehyde is a high melting solid.
