Question

1. Why cyclohexyl chloride has more dipole moment than aryl halide?
2. Why C-X bond in aryl halide is less polar than alkyl halide?
Explain with examples

Answer 1

1 AS WE KNOW DIPOLE MOMENT IS DIRECTLY PROPORTIONAL TO BOND LENGTH

CYCLOHEXYLCHLORIDE HAS SP3 HYBRIDIZATION AND ARYL HALIDE HAS SP2 HYPRIDIZATION WHICH MEANS THAT ARYL HALIDE HAS LOWER BOND LENGTH THUS LEADING TO LOWER DIPOLE MOMENT

2.DUE TO THE SP2 HYBRIDIZATION OF THE C-X BOND IN ARYL HALIDE THE LONE PAIR OF THE HALIDE ARE IN RESONANCE WITH THE RING DUE TO WHICH THEY ARE LESS RESPONSIVE TO NUCLEOPHILIC SUBSTITUTION AND HENCE THEY ARE LESS POLAR THEN ALKYL HALIDES

I HOPE THIS HELPS

Answer 2

Answer:

(i) In chlorobenzene, the C atom of the C-Cl bond is sp

2

hybridized and has more s character and electronegativity. In cyclohexyl chloride, the C atom of the C-Cl bond is sp

3

hybridized, has less s character and less electronegative. Hence, the C-Cl bond in chlorobenzene is less polar than the C-Cl bond in cyclohexyl chloride.

Also, in chlorobenzene, the lone pair of electron on the Cl atom is in resonance with a benzene ring. This gives partial double bond character to C-Cl bond and there is a decrease in the magnitude of partial negative charge on Cl atom. However, in cyclohexyl chloride, there is a C-Cl single bond. The dipole moment is a product of charge and distance. Also C-Cl bond with partial double bond character has lower bond length than with C-Cl single bond. Hence, chlorobenzene has lower dipole moment than cyclohexyl chloride.

(ii) Inter-molecular attractive forces present in alkyl halides are dipole dipole interactions and in case of water molecules, intermolecular hydrogen bonds are present. When alkyl halides are added to water, the intermolecular attractive force present between an alkyl halide and water molecules are weaker than the forces that are already present between two alkyl halide molecules and two water molecules. Hence, alkyl halides are water-immiscible.

(iii) Grignard reagents are highly reactive with moisture that is present in apparatus or starting materials. Hence, we should prepare Grignard reagents in the anhydrous condition.

RMgX+HOH→RH+MgOHX