Structural and Vibrational Investigation on a Benzoxazin Derivative with Potential Antibacterial Activity

In this chapter, the structural and vibrational properties of 2-(4- methylphenyl)-4H-3,1-benzoxazin-4-one were studied by using the available experimental infrared spectrum and the hybrid B3LYP/6-31G*and B3LYP/6- 311++G** methods. The bonds order, charge-transfers and stabilization energies for the compound were calculated employing the Natural Bond Orbital (NBO) analysis while the topological properties at the same levels of theory were calculated using the Atoms in Molecules theory (AIM). Furthermore, the frontier molecular HOMO and LUMO orbitals for the compound were also computed and later the values were compared with those reported for 2-(4-chlorophenyl)-4H-3,1-benzoxazin-4-one and 2-phenyl-4H-3,1- benzoxazin-4-one. On the other hand, the harmonic vibrational frequencies at the same levels of theory were calculated using the optimized geometries of the compound. Then, the Pulay´s scaled quantum mechanical force field (SQMFF) methodology was used together with the corresponding normal internal coordinates in order to perform the complete assignment of the vibrational spectra. In addition, the scaled force constants were also presented together with the force fields by using both levels of approximation. In this chapter, the Raman spectrum for the compound at the B3LYP/6-31G* level of theory was predicted.

Keywords: 1-benzoxazin-4-one, 2-(4-methylphenyl)-4H-3, DFT calculations, force field, molecular structure, vibrational spectra.