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Question
Why is the boiling point of o-dichlorobenzene higher than p-dichlorobenzene, but the melting point of para-isomer is higher than ortho-isomer?
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Solution
Because o-dichlorobenzene has a greater dipole moment and a greater dipole-dipole interaction than p-dichlorobenzene, it has a higher boiling point.

Boiling point
As opposed to ortho- and meta-isomer, p-dichlorobenzene has a higher melting point than that of o- and m-isomer due to its greater symmetry, which suits the crystal better.
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