Arrange the following in decreasing order of their acidic strength and give reason for your answer.
CH3CH2OH, CH3COOH, ClCH2COOH, FCH2COOH, C6H5CH2COOH
The decreasing order of their acidic strength:
FCH2COOH > ClCH2COOH > C6H5CH2COOH > CH3COOH > CH3CH2OH.
EXPLAINATION:
We know carboxylic acids are more acidic than alcohols of comparable molecular masses. So, CH3CH2OH is least acidic among the given compounds.
Electron withdrawing groups increase 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.
Thus, FCH2COOH and ClCH2COOH are highly acidic due to the –I effect of halogen. FCH2COOH is most acidic among the given compounds due to the higher electronegativity of Fluorine atom.
C6H5CH2COOH is more acidic than CH3COOH due to the resonance in C6H5CH2COOH.
Thus, the decreasing order of their acidic strength is:
FCH2COOH > ClCH2COOH > C6H5CH2COOH > CH3COOH > CH3CH2OH.