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Which is more acidic between trichloromethane and triflouromethane and why?

Which is more acidic between trichloromethane and triflouromethane and why?

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1 Answers

Godfrey Classic Prince
633 Points
9 years ago

Dear Himanshi Sharma,

We know that Fluorine(F) is more electronegative than Chlorine(Cl) .Therefore -I effect(Inductive Effect) of Fluorine(F) would be more and Trifluoromethane(CHF3) would be more acidic.

But this is not the case. As -M(Mesomeric Effect) effect also plays an important role in determining the acidity.We also know that -M(Mesomeric Effect) is considered over -I(Inductive Effect).

Now,If we compare the conjugate base of both the given molecules, C-Cl3 and C-F3, Chlorine(Cl) has vacant 3d orbitals whereas Fluorine(F) does not have any vacant d orbitals,infact it does not even have d-orbitals. Therefore Chlorine(Cl) can exert -M effect(Mesomeric Effect) due to availability of vacant d orbital but Fluorine(F) cannot exert the -M effect(Mesomeric Effect). -M effect(Mesomeric Effect) stabilises the negative charge and increases acidic strength. Therefore Trichloromethane(CHCl3) is more acidic than Trifluoromethane(CHF3).

 

Hope this helped you immensely..!!

All the Very Best & Good Luck to you...!!

 

Best Regards,

AskIITians Expert,

Godfrey Classic Prince

IIT-M

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