Question

Give reasons:
(i) $C-Cl$ bond length in chlorobenzene is shorter than $C-Cl$ bond length in $C{H}_3-Cl$.
(ii) The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.
(iii) $S_{N}1$ reactions are accompanied by racemization in optically active alkyl halides.

Answer 1

(i) As shown in the image the lone pair on chlorine shows delocalization of electrons by resonance in chlorobenzene attribute for partial double bond character due to which bond length is shorter than a single bond.

(ii) The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride because the polarity of $C-Cl$ bond in chlorobenzene is less due to $C$ is $s{p}^2$ hybridized (more s character) while in cyclohexyl chloride where it is $s{p}^3$ hybridized.

(iii) In $S{N}^1$ reactions the nature of carbocation formed is planar. Thus the nucleophile can attack from either side resulting in the formation of both enantiomers. The product is a racemic mixture of an equal proportion of two optically active enantiomers.