Stability of Carbocation, Carbanion & Free radical (Application of I Effect)

Application of I-Effect

I. Stability of Carbocation, Carbanion & Free radical (Basis I-Effect)

Carbocation & carbon free radical both have incomplete octet so both have similar tendency to gain electrons or both have similar order of stability.

Carbocation & carbon free radical both have similar tendency to gain electrons or both have similar order of stability.

Special Point:-

Stability  ∝   1/{quantity of charge (+q or -q) }

Energy = (kq²)/r  ∝  q² 

I.e.  Charge increase --> Energy increase --> Reactivity increase  -->  Stability decrease

Examples:-

Stability Order 

  1. CH₃---C⁺H---CH₃     >  CH₃---C⁺H₂  >  NO₂—CH₂—C⁺H₂

       Less +ve charge                                       More +ve charge     

       More stable                                              Less stable

  2.CH₃---C^-H---CH₃  <  CH₃---C^-H₂  <  NO₂—CH₂—C^-H₂

       More -ve charge                                      Less -ve charge     

       Less stable                                               More stable

Question:-

Arrange the following in correct order of stability-

1.      a. N⁺H₃—CH₂—C⁺H₂   b. Cl—CH₂—C⁺H₂  c. CH₃—CH₂—C⁺H₂

 Less +ve charge

  More stable

            Stability order :- c > b > a

2.       a. COO^-—CH₂—C^-H₂   b. CH₃—CH₂—C^-H₂   c. CN—CH₂—C^-H₂

  Less –ve charge

  More stable

            Stability order:- c > b > a

3. 

4.

Special points:-

*Stability order of Carbocation

(CH₃)₃C⁺  >  (CH₃)₂C⁺  >  CH₃C⁺  >  C⁺H₃

       3'C  >   2'C  >  1'C  >  Methyl carbocation

*Stability order of carbanion

   (CH₃)₃C^-  <  (CH₃)₂C^-  <  CH₃C^-  <  C^-H₃

    3'C  <  2'C  <  1'C  <  Methyl carbanion

 *Stability order of Carbon free radical

   (CH₃)₃C^*  >  (CH₃)₂C^*  >  CH₃C^*  >  C^*H₃

    3'C  >   2'C  >  1'C  >  Methyl free radical