Question

p - dichlorobenzene has higher melting point than o and m isomers. why ?

Answer 1

p-dichlorobenzene has higher melting point than ortho and para isomers, due to its symmetrical structure.
Additional stability is available to p-dichlorobenzene due to its symmetry.

Answer 2

Hey !!

The p-isomers being more symmetrical fits closely in the crystal lattice and thus has stronger intermolecular forces of attraction than o- and m-isomers. As during melting, the crystal lattice breaks, therefore, a larger amount of energy is needed to melt the p-isomer than the corresponding o-and m-isomers.

In simple words, the melting point of the p-isomer is higher than the corresponding o- and m-isomers.

Hope it helps you !!