Question

Why does p-dichlorobenzene has higher m.p. than o- and m- isomers?

Answer 1

The p- isomers being more symmetrical fits closely in the crystal lattice and thus has stronger inter-molecular forces of attraction than o- and m- isomers .

As during melting or dissolution , the crystal lattice breaks , therefore a large amount of energy is needed to melt or dissolve the p - isomer than the corresponding o-and m-isomers .

In other words , the melting point to the p- isomers is higher and its solubility lower than the corresponding o- and- m- isomers


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Answer 2

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p-Dichlorobenzene has higher m.p. and solubility than those of o- and m-isomers.

This is because p-isomer is more symmetrical and hence magnitude of molecular forces of attraction are stronger, therefore, the p-isomer melts at a higher temperature and has comparatively more solubility.