A theoretical vibrational spectroscopic investigation on free Ethyl 2- and 3-aminobenzoate molecules

The possible stable conformers of free Ethyl 2- and 3-aminobenzoate molecules were searched via subsequent single point energy calculations carried out at semi-empirical PM3 theory level. The final equilibrium geometrical parameters for the obtained stable conformers were defined by performing geometry optimizations with B3LYP hybrid DFT method and basis sets of different size and type. The harmonic vibrational normal modes of the two molecules and their corresponding wavenumbers and IR intensities were calculated at the obtained equilibrium geometries using the same method and basis sets used in the geometry optimizations. In the light of these calculated spectral data, a successful assignment for the fundamental bands in the IR spectra of the two molecules was given. In order to fit the calculated harmonic wavenumbers to the experimentally observed ones, two different scaling procedures, called “scaling wavenumbers in Scaled Quantum Mechanics Force Field (SQM FF) methodology” and “scaling wavenumbers with dual empirical scale factors”, were proceeded independently.