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4. The pKa values of the ortho, para, and meta substituted benzoic acids are shown below. Use words and drawings to explain t

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Since pKa is -logKa therefore pKa is inversely proportional to Ka ,that is acidity.

Acidity of substituted benzoic acid means the ability of substituted benzoic acid to donate protons ( H+ ) from carboxyl group , in benzoic acid substituted by amine group,the amine group is electron donating group so if removal of a proton gives a less stable carbanion then it is less acidic and hence has a large pka values.

For example, ortho amino benzoic acid has largest pka value and is least acidic as seen from below structures since amine group is very near to the carbanion the electron donation is much easier and it destabilizes the carbanion the most and is least acidic and more pka value (4.95) :

On dori n Họ H . Nh [17 (Proton din (Proton donation) (Destabilized Carbanin In para amino benzoic acid after donation of a proton , it is destablized by the amino group but the affect is less in compared to ortho substituted benzoic acid since the amine group is not near to the carbanion generated as shown and so its pka value(4.89) is less or more acidic than ortho substituted benzoic acid :

Col Posoton nation) Can (Destable Carbarion) NH

Meta amino benzoic acid on the other hand has no such destabilizing affect of carbanion by donation of proton and hence is most acidic and has least pka value(4.73) :

0 -CORT -HⓇ -rim -nim m (Proton ration) soton donatio Him (No destabilizing affects)

So above reason signifies the relative values of pka for amino substituted carboxylic acids.

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