Question

Account for the following:
(a) The C–Cl bond length in chlorobenzene is shorter than that in methyl chloride.
(b) Grignard reagents should be prepared under anhydrous conditions.
(c) In case of optically active alkyl halides, S_N1 reactions are accompanied by racemisation.

Hint:

Racemization is a characteristic feature of SN\textsubscript{1} reactions due to the planar nature of the carbocation intermediate.

Answer 1

(a) The C-Cl bond length in chlorobenzene is shorter than that in methyl chloride.
The C-Cl bond in chlorobenzene is shorter due to the delocalization of the electron density into the aromatic ring, which stabilizes the bond, making it stronger and shorter compared to methyl chloride.
(b) Grignard reagents should be prepared under anhydrous conditions.
Grignard reagents are highly reactive and will react with water to form hydrocarbons and magnesium hydroxide. To avoid this, Grignard reagents should be prepared in anhydrous conditions to prevent the reaction with moisture.
(c) In case of optically active alkyl halides, SN1 reactions are accompanied by racemisation.
SN1 reactions involve the formation of a carbocation intermediate. This intermediate can undergo attack from either side, leading to the formation of both enantiomers and thus racemization.