bascicity of toludine
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As expected from Inductive(/hypercojugative) as well as ortho effect the basicity order should be: ortho-toluidine>para-toluidine>meta-toluidine. But,experimental order is: para-toluidine(Pka=5.12)>meta-toluidine(Pka=4.69)>ortho-toluidine(Pka=4.39).
The order of basicity is explained by two opposing effects :i) inductive effect ii) Stability of the conjugate base. Here 2nd factor is more significant for ortho-toluidine & 1st factor is important for para-toluidine. For ortho-toluidine the conjugate base [o-MeC6H4NH3+] is destabilized by steric interactionbetween -NH3+ & -Me(at ortho). This desatabilization is absent with para-toluidine & meta-toluidine.Tha's why basicity of:ortho-toluidine(Pka=4.39)< para & meta isomer.On the other hand,in meta toluidine only +I of Me is operative whereas in para-toludine both hypercojugative & +I of Me is operative, that's why basicity of:para-toluidine(Pka=5.12)>meta-toluidine(Pka=4.69).
As expected from Inductive(/hypercojugative) as well as ortho effect the basicity order should be: ortho-toluidine>para-toluidine>meta-toluidine. But,experimental order is: para-toluidine(Pka=5.12)>meta-toluidine(Pka=4.69)>ortho-toluidine(Pka=4.39).
The order of basicity is explained by two opposing effects :i) inductive effect ii) Stability of the conjugate base. Here 2nd factor is more significant for ortho-toluidine & 1st factor is important for para-toluidine. For ortho-toluidine the conjugate base [o-MeC6H4NH3+] is destabilized by steric interactionbetween -NH3+ & -Me(at ortho). This desatabilization is absent with para-toluidine & meta-toluidine.Tha's why basicity of:ortho-toluidine(Pka=4.39)< para & meta isomer.On the other hand,in meta toluidine only +I of Me is operative whereas in para-toludine both hypercojugative & +I of Me is operative, that's why basicity of:para-toluidine(Pka=5.12)>meta-toluidine(Pka=4.69).
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