Nucleophilic substitution reaction (SN2 &SN1) of haloalkane|Class_12||CBSE|CHSE||JEE|NEET| By JB Sir

(i) Nucleophilic substitution reactions:::
In this type of reaction, a nucleophile reacts with haloalkane (the
substrate) having a partial positive charge on the carbon atom bonded to halogen. A substitution reaction takes place and halogen atom,
called leaving group departs as halide ion. Since the substitution
reaction is initiated by a nucleophile, it is called nucleophilic
substitution reaction.

It is one of the most useful classes of organic reactions of alkyl
halides in which halogen is bonded to sp3 hybridised carbon

Groups like cyanides and nitrites possess two nucleophilic centres
and are called ambident nucleophiles. Actually cyanide group is a
hybrid of two contributing structures and therefore can act as a
nucleophile in two different atoms i.e., linking through
carbon atom resulting in alkyl cyanides and through nitrogen atom
leading to isocyanides. Similarly nitrite ion also represents an ambident
nucleophile with two different points of linkage The linkage
through oxygen results in alkyl nitrites while through nitrogen atom
it leads to nitroalkanes.

Substitution nucleophilic bimolecular (SN2)
The reaction between CH3Cl and hydroxide ion to yield methanol and
chloride ion follows a second order kinetics, i.e., the rate depends
upon the concentration of both the reactants .
it depicts a bimolecular nucleophilic displacement (SN
2) reaction;
the incoming nucleophile interacts with
alkyl halide causing the carbon-
halide bond to break while forming a new carbon-OH bond

STEREOCHEMISTRY:: inversion of configuration for SN2.
Racemic mixture for SN1
INTERMEDIATE:: transition state for SN2
Carbocation for SN1