chlorobenzene

[binayakafle]

Why C-Cl bond of Chlorobenzene stronger than that of chloroethane?
i tried so hard but couldnot solve.. plz help

[Zuzka]

Hi, when Cl is on aromatic system (like in chlorbenzene) it has a weak positive mesomeric effect on it, that means, Cl is a weak electron donor. Even if the electrons from the carbon are pulled to more electronegative chlorine, Cl also offers its lone el. pair to the unsaturated aromatic system. The electron density from Cl el. pair is than shared throughout the system. The molecule stabilises and the bond is stronger, while more electrons are involved.This can not happen in chloroethane, while it is saturated(no double bonds..), there the lone el. pairs can not be involved in bonding and the Cl-C bond is weaker.