sp² hybrid carbon(s-character=33.33%) in chlorobenzene is more electronegative than a sp³-hybrid carbon(s-character=25%) in cyclohexylchloride, due to greater s-character. Thus, Carbon atom of chlorobenzene has lesstendency to release electrons to Cl than carbon atom of cyclohexylchloride.

As a result,C-Cl bond in chlorobenzene is less polar than in cyclohexylchloride. Further due to delocalisation of lone pairs of electrons of the Cl atom over the benzene ring, C-Cl bond in cholorobenzene acquires some double bond character while the C-Cl in cyclohexylchloride is a pure single bond. In other words, C-Cl bond in chlorobenzene is shorter than in cyclohexylchloride. Since the dipole moment is a product of charge and distance, therefore, chlorobenzene has lower dipole moment than cyclohexylchloride due to lower magnitude of negative charge on the Cl atom and shorter C-Cl distance.(double bond is of shorter length than single bond)