|Class 12 Chemistry Haloalkanes and Haloarenes||Organometallic Compounds|
Most organic chlorides and iodides react with certain metals to give compounds containing carbon-metal bonds called organo-metallic compounds.
For example, RMgX is referred to as Grignard Reagent in 1900 by Victor Grignard.
Carbon-magnesium n=bond is covalent but highly polar.
Grignard reagents are highly reactive and react with any source of proton to give hydrocarbons.
Nucleophilic Substitution: Resonance effect
Aryl halides are extremely less reactive towards Nucleophilic substitution reactions. Let us now discuss resonance effect.
Nucleophilic Substitution:sp2 hybridised
C-X bond in halo alkane is 177 Pico meter. Whereas C-X bond in haloarenes is 169 Pico meter. Therefore the C-x bond in haloarenes is strong and stable and hence difficult to break. Hence the Nucleophilic substitution in haloarenes is difficult.
Nucleophilic Substitution: unstable cation
In figure II resonance structure is not possible. Cation formation is not possible as the cation is unstable.
This shows that SN1 is totally ruled out.
SN2 is possible.