Three aminomethylbenzoic acid derivatives were theoretically studied at M062X/6-311++G(d,p) level in vacuum, namely 2-ammonio-5-methylcarboxybenzene perchlorate (1), 4-(ammoniomethyl) carboxybenzene nitrate (2) and 4-(ammoniomethyl) carboxybenze perchlorate (3). The compounds’ structures were fully-optimized and compared with the single-crystal x-ray diffraction results, showing a very close agreement with the experimental structural parameters. Their IR, ¹H- and ¹³C-NMR spectra were calculated and examined in detail. Furthermore, the molecular electrostatic potential (MEP) maps of the studied compounds were investigated and the strength of the non-covalent interactions evaluated. In addition to these results, the NLO properties of the three compounds were predicted.