How Do The Observed Melting Points Of The Benzoic, Fumaric, And Salicylic Acid Relate With Their Structures?
Melting and boiling points are directly related to the strength of the bonds between molecules. If something has a higher melting point than if will have stronger (or sometimes the same strength but more of them) bond between two of the molecules of that type. Fumaric acid has lots of hydrogen bonding (very strong, uniquely describes type of dipole dipole bonding) between the hydroxyl and the other oxygen type (C=O). Benzoic is self complementary so 2 of the molecules will lock into place next to each other quite well with hydrogen bonding but still not as well as salicylic acid. Benzoic would have lowest of the three due to still having less interactions between 2 molecules than in the other 2 and Fumaric would have the highest. When answering a Q on Melting or boiling point it is always key to refer back to the structure of the molecule only in terms of how well it can bond (inter molecular bonds) to another molecule which is exactly the same as itself.
