Question

Why is the melting point of benzoic acid (mp = 122.41°C) so much higher than the mp of benzene (5.5°C) when their structures are extremely similar?

Answer 1

High molecular symmetry is associated with high melting point. Benzene has six carbon atoms of one single chemical type. Some single substituted benzenes have lower melting points than benzene itself, despite the increase in molar mass and polarity and this is due to higher symmetry of benzene compared to the substituted ones. However, if the substituent brings in strong polar interactions like H – bonding as in benzoic acid, symmetry as a factor becomes less important. Due to this stong Hydrogen bonding benzoic acid has greater melting point then benzene when they have similar structure.