(i) (a) In order to understand the lower dipole moment of chlorobenzene we need to look into the contributing structures of the molecules.(b) From the above structures we find that the C – Cl bond in chlorobenzene has a partial double bond character (structure II, III and IV). As a result, the C – Cl bond length here isshorter than the C – Cl single bond but longer than the C – Cl doublebond.
(c) Also evident is the positive charge on Cl atom which reduces the partial negative (δ–) charge which it is expected to carry by the virtue of its electronegativity.
(d)Consequently, the dipole moment, which is a product of bond length and partialnegative charge on Cl atom, reduces.
However, in cyclohexyl chloride this does not happen. It is an alkyl halide and carbon is purely sp3 hybridised and C – Cl bond has the bond length of a single bond and δ− appearing on Cl is also higher, thus, the greater dipole moment.
(ii) Only those compounds which can form hydrogen bonds with water are miscible with it. Alkyl halides, though polar due to the presence of electronegative halogen atom, are immiscible since they cannot form hydrogen bonds.
(iii) Grignard reagents R – Mg – X is a class of highly reactive compounds which can extract a proton even from water molecule. They thus, turn into the corresponding alkanes and render any other desired reaction ineffective.
This is why Grignard reagents are prepared in the absolute absence of water (anhydrous conditions). (e.g.,)