Nucleophilic Substitution Reaction
Nucleophile :- (nucleus loving) It contain negative charge or unshared electron which attract positive part of the atom called nucleus that's why called nucleus loving because opposite charges attract each other .
A negative ion or molecule with an unshared electron pair which can donate an electron pair to an electron -deficient center in a reaction is called nucleophile (nucleophilic regent )
Example :- Cl,Br,OH,CN,H2O,NH3
Electrophile :- (electron loving) It has deficient electron it need electron so the charge on this species is positive it attract towards negative charge (electron)
A species that accept an electron pair from a electron rich center in a reaction is called an electrophile (electrophilic regent)
Example :- H+, NO+, cation
Substrate :- A reaction that is attacked by the regent is called a substrate
Leaving group :- The part of the substrate that departs along with the electron pair is called leaving group
Example :-
OH + CH3Br _________ CH3OH + Br
Nucleophile substrate leaving group
Nucleophilic Substitution Reaction
A reaction in which one nucleophile (Nu:) displaces another nucleophile (X-) from combination with an electrophilic carbon atom is called a nucleophilic substitution reaction.
It is donated by SN S stand for substitution and N for nucleuphilic.
Nu: + R-CH2-X ________ R-CH2-Nu + X:
Nucleophilic Substitution Reactions are of two types
SN2 SN1
i) (Nucleophilic substitution bimolecular) i) (Nucleophilic Substitution unimolecular)
ii) SN2 is one step mechanism ii) SN1 is two step mechanism
iii) The attack of Nu: on carbon and the iii) In the first step substrate ionize and in the
departure of Halide Ion take place at second step Nu: attack on the carbocation
the same time in a single step
iv) Nu: attack on carbon only from he back side iii) Nu: can attack both side
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Explanation of SN1 and SN2 reactions :-
In Sn1 Reaction first step the substrate ionize reversibly and formed a carbocation because in SN1 reaction there is tertiary alkyl halide (CH3)3 when halide ion departure from the Tertiary carbon SN1 reaction take place only in tertiary carbon because three carbon are attached with the alpha carbon they will donate electron to the Alpha carbon to over come the deficiency of electron so carbocation will be more stable
In the next step Nu: attack on this carbocation either from the back side or from the front side it make the product
CH3 CH3
! ! +
Step 1 CH3----C-----Br _____ CH3-----C (CARBOCATION)
! !
CH3 CH3
Step 2 CH3 CH3
!+ !
CH3 --C + OH (Nu:) _______ CH3-----C----OH
! !
CH3 CH3
In SN2 reaction the reaction is complete in only one step halide ion departure from the substrate carbon and Nu: attack at the same time
H H
! !
OH + H__ C__Cl ________ OH ------C-----Cl
! ! ! H
H H
We can see that OH and Cl bond bond breaks at the same time because this reaction is happened on one step so Nu: attack only on the back side because at the front side Cl is attached with the carbon
Hope you got it ? if there is any problem you can ask me via email
Published by Adil khan (mak)
Nucleophile :- (nucleus loving) It contain negative charge or unshared electron which attract positive part of the atom called nucleus that's why called nucleus loving because opposite charges attract each other .
A negative ion or molecule with an unshared electron pair which can donate an electron pair to an electron -deficient center in a reaction is called nucleophile (nucleophilic regent )
Example :- Cl,Br,OH,CN,H2O,NH3
Electrophile :- (electron loving) It has deficient electron it need electron so the charge on this species is positive it attract towards negative charge (electron)
A species that accept an electron pair from a electron rich center in a reaction is called an electrophile (electrophilic regent)
Example :- H+, NO+, cation
Substrate :- A reaction that is attacked by the regent is called a substrate
Leaving group :- The part of the substrate that departs along with the electron pair is called leaving group
Example :-
OH + CH3Br _________ CH3OH + Br
Nucleophile substrate leaving group
Nucleophilic Substitution Reaction
A reaction in which one nucleophile (Nu:) displaces another nucleophile (X-) from combination with an electrophilic carbon atom is called a nucleophilic substitution reaction.
It is donated by SN S stand for substitution and N for nucleuphilic.
Nu: + R-CH2-X ________ R-CH2-Nu + X:
Nucleophilic Substitution Reactions are of two types
SN2 SN1
i) (Nucleophilic substitution bimolecular) i) (Nucleophilic Substitution unimolecular)
ii) SN2 is one step mechanism ii) SN1 is two step mechanism
iii) The attack of Nu: on carbon and the iii) In the first step substrate ionize and in the
departure of Halide Ion take place at second step Nu: attack on the carbocation
the same time in a single step
iv) Nu: attack on carbon only from he back side iii) Nu: can attack both side
Explanation of SN1 and SN2 reactions :-
In Sn1 Reaction first step the substrate ionize reversibly and formed a carbocation because in SN1 reaction there is tertiary alkyl halide (CH3)3 when halide ion departure from the Tertiary carbon SN1 reaction take place only in tertiary carbon because three carbon are attached with the alpha carbon they will donate electron to the Alpha carbon to over come the deficiency of electron so carbocation will be more stable
In the next step Nu: attack on this carbocation either from the back side or from the front side it make the product
CH3 CH3
! ! +
Step 1 CH3----C-----Br _____ CH3-----C (CARBOCATION)
! !
CH3 CH3
Step 2 CH3 CH3
!+ !
CH3 --C + OH (Nu:) _______ CH3-----C----OH
! !
CH3 CH3
In SN2 reaction the reaction is complete in only one step halide ion departure from the substrate carbon and Nu: attack at the same time
H H
! !
OH + H__ C__Cl ________ OH ------C-----Cl
! ! ! H
H H
We can see that OH and Cl bond bond breaks at the same time because this reaction is happened on one step so Nu: attack only on the back side because at the front side Cl is attached with the carbon
Hope you got it ? if there is any problem you can ask me via email
Published by Adil khan (mak)
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