Analysis of the structure and the FT-IR and Raman spectra of 2-(4-nitrophenyl)-4H-3,1-benzoxazin-4-one. Comparisons with the chlorinated and methylated derivatives

Abstract In this work, the structural, topological and vibrational properties of the monomer and three dimers of the 2-(4-nitrophenyl)-4H-3,1-benzoxazin-4-one (NPB) derivative were studied combining the experimental FTIR and FT-Raman spectra in the solid phase with DFT calculations. Here, Natural Bond Orbital (NBO), Atoms in Molecules (AIM) and HOMO and LUMO calculations were performed by using the hybrid B3LYP/6-31G*and B3LYP/6-311++G** methods in order to compute those properties and to predict their reactivities. The comparisons with the properties reported for the chlorinated (Cl-PB) and methylated (CH 3 -PB) derivatives at the same levels of theory can be clearly justified by the activating (CH 3 ) and deactivating (NO 2 and Cl) characteristics of the different groups linked to oxaxin rings. The NBO and AIM studies evidence the following stability orders: Cl-PB > NO 2 -PB > CH 3 -PB in very good concordance with the f(νC23-X26) force constants values. The frontier orbitals analyses reveal that the Cl-PB and NO 2 -PB derivatives have good stabilities and high chemical hardness while CH 3 -PB has a higher chemical reactivity. On the other hand, the complete vibrational assignments for monomer and dimers species of NPB were presented. The presence of the IR bands at 1574 and 1037 cm −1 and, of the Raman bands at 1571 and 1038 cm −1 support clearly the presence of the different dimeric species proposed for NPB.