Glycine exists as `NH_(3)""^(+)CH_(2)COO^(-)` , zwitter ion but anthranilic acid (p-amino benzoic acid) does not exist as zwitter ion. Why?

Explanation

In o- or p -aminobenzoic acids , the lone pair of electrons on the `NH_2` group is dontateed towards the benzene ring. As a result , acidic character of `-COOH` group and basic character of `-NH_(2)` group decreases. Therefore the weakly acidic `-COOH`group cannot transfer a `H^(+)` ion to the weakly basic `-NH_2` group. Thus, o-or p-aminobenoic acids do not exist as zwitterions.

However , in glycine , no such electron -withdrawing benzene ring is present . As a result , `-NH_2` group is sufficiently basic and hence accepts a proton form `-COOH` group to form a zwitterion.
`underset("Glycine")(H_2N-CH_2-COOH) hArrH_(3)overset(+)N-CH_2-COO^(-)` .