explain in detail about SN1 and SN2 reactions

NIKHIL GARG Grade: 12

        explain in detail about SN1 and SN2 reactions

8 years ago

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vikas askiitian expert

509 Points

							SN1 ) this reaction proceeds  according to these steps
1) hetrolatically cleavage of carbon halogen bond
2)formation of carbocation(rearrangment)
3)formation of new bond
eg) CH₃CH₂CH_2Cl + KOH (aq) = CH₃CH(OH)CH₃
mechanism
   CH₃CH₂CH2Cl  =  CH₃CH_{2CH2⁺       ( 1^O CARBOCATION)}
 1^o carbocation rearranges to 2^o by hydride shift , to gain stablity ...
    CH₃CH⁺CH₃ + OH^- (neucleophile) = CH₃CH(OH)CH₃
order of reactivity  = benzyl>allyle>3^o >2^o>1^o                  (on the basis of carbocation stablity))
 
SN2)
in this reaction breaking of bonds & formation of new bonds take place samultaneously during a transition state...
in this state neuclephile(OH^-) attacks from back side and at the same time carbon halogen bond breaks and product is formed...
this transition state is pentavalent & attaking neuclophile ,halogen are  along axial bond ......no rearrangment occures...
eg)
     CH₃CH₂CH₂Cl + OH^- => CH₃CH₂CH₂OH
this reaction favoures  aprotic solvents & strong base ......
order of reactivity = 1⁰>2^o>3⁰              (less staric hindered alkyle halide will react fast )