The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride. Explain.

Explanation

As chlorine is more electronegative, than carbon the C-Cl bond is polar in nature with a slight negative charge (`delta^(-)`) on chlorine atom and corresponding slight positive charge (`delta^(-)`) on carbon atom.
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However, the dipole moment of chlorobenzene is lower than that of cyclohexyl chloride. It is because C-Cl bond-in chlorobenzene is less polar than similar bond in cyclohexyl chloride, it is mainly due to following two reasons. (a) Due to resonance : Due to resonance in chlorobenzene, the lone pair of electrons on chlorine atom is delocalised over the benzene ring. In 3 out of the 5 resonance structures chlorine has a positive charge. This reduces the magnitude of negative charge on chlorine atom and lience the polarity of C-Cl bond.

(b) Due to different states of hybridisation of C-atom. In chlorobenzene carbon atom is `sp^2`-hybridised while in cyclohexyl chloride, carbon atom is `sp^2 `-hybridised. As electronegativity of sp2-hybridised C-atom is more than that of `sp^3` -hybridised C atom, it decreases the magnitude of negative charge on chlorine atom in chlorobenzene. This decreases the polarity of the C-Cl bond in chlorobenzene and hence its dipole moment.