Which acid of each pair shown here would you expect to be stronger?

(i) CH3CO2H or CH2FCO2H 

(ii) CH2FCO2H or CH2ClCO2H

(iii) CH2 FCH2 CH2 CO2H or CH3 CHFCH2 CO2H

<p><strong> (i)</strong> The +I effect of –CH₃ group increases the electron density on the O-H bond. Therefore, the release of proton becomes difficult. On the other hand, the -I effect of F decreases the electron density on the O-H bond. Therefore, the proton can be released easily. Hence, CH₂FCO₂H is a stronger acid than CH₃CO₂H.</p><p><strong> (ii)</strong> F has stronger -I effect than Cl (as fluorine is more electronegative than chlorine). Therefore, CH₂FCO₂H can release proton more easily than CH₂ClCO₂H. Hence, CH₂FCO₂H is a stronger acid than CH₂ClCO₂H.</p><p><strong> (iii)</strong> Inductive effect decreases with increase in distance (the more will be the distance of the inductive group from the carboxylic group less will be its effect of polarisability). Hence, the -I effect of F in CH₃CHFCH₂CO₂H is more than it is in CH₂FCH₂CH₂CO₂H . Hence, CH₃CHFCH₂CO₂H is a stronger acid than CH₂FCH₂CH₂CO₂H .</p><p><strong> (iv)</strong> Due to the -I effect of F (being electronegative), it is easier to release proton in the case of compound (A). However, in the case of compound (B), the release of the proton is difficult due to the +I effect of –CH₃ e. methyl group. Hence, (A) is a stronger acid than (B).</p>

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