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

Explanation

In chlorobenzene the C of C - Cl bond in `sp^2` hybridised while C - Cl bond in cyclohexyyl chloride `sp^3` hybridisation.

Therefore the `sp^2` hybridised C of chlorobenzene has more s character and hence more electron negative than the `sp^3` hybridised C of eyelohexyl chloride. As a result the `sp^2` hybrid of C - Cl bond in chlorobenzene has less tendency to release electron to Cl than the `sp^3` hybrid carbon of cyclohexyl chloride. As a result, the C - Cl bond in chlorobenzene is less polar than in cyclohexyl chloride. Thus chlorobenzene is less polar than cyclohexyl chloride.
In other words the magnitude of negative charge `(delta-)` is less on Cl atom of chlorobenzene than in cyclohexyl chloride. Further due to delocalisation of lone pair of electron of the chlorine atom over the benzene ring due to resonance, C - Cl bond in chlorobenzene acquire some double bond character. On the other hand C - Cl bond in cyclohexyl chloride is a pure single bond.

Since dipole moment is a product of charge and distance therefore chlorcibenzene has lower dipole moment than cyclohexyl chloride due to lower magnitude of charge (`delta-`) on Cl atom and small C - Cl distance.