Arrange the following in decreasing order of their acidic strength. Give explanation for the arrangement.
C6H5COOH, FCH2COOH, NO2CH2COOH
The decreasing order of their acidic strength:
NO2CH2COOH > FCH2COOH > C6H5COOH.
EXPLAINATION:
Electron withdrawing groups like -NO2, increases the acidity of carboxylic acids by stabilizing the conjugate base through resonance effects, whereas, electron-donating groups decrease the acidity of carboxylic acids by destabilizing the conjugate base through resonance.
We know that the negative inductive effect of nitro group is greater than that of the fluorine atom.
Thus, NO2CH2COOH is most acidic among the given three compounds.
Hence, the decreasing order in terms of their acidic strength is:
NO2CH2COOH > FCH2COOH > C6H5COOH.