SN2-REACTIONS
SN2-REACTIONS
    In SN2-REACTIONS, the formation of the carbon-nucleophile bond [C--Nu] and the cleavage of the     carbon- halogen bond [C--X] occur simultaneously.
    These are nucleophilic substitution reactions which occur in one step .
MECHANISM
 
    The reaction proceeds in one step. The attack of nucleophile and release of halide group take place     at the same time.i.e
Nu- + R-X ® [NuRX] ® R--Nu + X-
Transition state
    Reactions of secondary alkyl halide may be SN1 or SN2 depending upon the nature of solvent.
RATE OF SN1-REACTIONS
 
    The rate of an SN2 reactions depend on the concentrations of nucleophile and the substrate.
    i.e       Rate of reaction = k[substrate][Nu]
    Since both substrate and nucleophile are present in rate expression therefore ifst is a bimolecular     reaction. It may be defined as "a bimolecular nucleophilic substitution reaction which occur in one     step .
FACTORS AFFECTING THE NATURE Of SN REACTIONS
 
   The mechanism of SN-reactions depend upon :
    The structure of alkyl group
    Nature of the solvent
     Structure Of Alkyl Group
    Reactions of primary alkyl halides take place in SN2 mechanism.
    Reactions of tertiary alkyl halides take place in SN1 mechanism.
    Reactions of secondary alkyl halides take place both in SN1 and SN2 mechanism but it depends upon     the nature of solvent.
    The order of stability of carbonium ion is as under:
    R3C+[tertiary carbonium ion]>R2C+H[secondary carbonium ion]>RC+H2[primary carbonium ion]
    Nature Of Solvent:A polar solvent favours SN1 mechanism due to capability of ionization where as     a non- polar solvent favours SN2 mechanism.
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