Question

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

Answer 1

Dear student,

The p-isomer of dichlorobenzene has a symmetrical structure, therefore, the molecules can closely pack in the crystal lattice. The intermolecular forces of attraction are strong and therefore a large amount of energy is required to break the bonds. Therefore the p-isomer melts at a higher temperature compared to ortho and meta isomers (having unsymmetrical and less packed crystal structure)

The lower solubility of p-dichlorobenzene can be explained as follows:
Due to the symmetrical structure of p-dichlorobenzene, it has zero dipole moment and thus is more non-polar than o and m- isomers which have non-zero(positive) dipole moments. Thus, para isomers have a lower solubility in water(polar) than o and m isomers. These dissolve more readily in non-polar(organic) solvents.

Regards