Question

o-Hydroxybenzaldehyde is a liquid at room temperature while p-hydroxybenzaldehyde is a high melting solid because of:

• A. $H-$bonding
• B. ionisation energy
• C. electron gain enthalpy
• D. lattice enthalpy.

Answer 1

Answer: (A)

$H-$bonding

Comparision between intramolecular hydrogen bond and intermolecular hydrogen bond=

Intramolecular forces are the forces that hold atoms together within a molecule. Intermolecular forces are forces that exist between molecules.

intermolecular: when the attraction is between two distinct molecules of same or different compounds. For example, between two molecules of $H_{2}O$ or between a molecule of $H_{2}O$ and a molecule of $N{H}_3$.

Intramolecular: when such attraction is among two parts of a molecule. For example, $H$ of the hydroxyl group is attracted by $O$ of the nitro group in o-nitrophenol.

Intermolecular H-bonding increases intermolecular attraction hence increases boiling point, viscosity and surface tension.

Whereas, intramolecular H-bonding tends to decrease the surface area of the molecule hence decreases boiling point and surface tension.

So the correct option is [A].