Structural-dynamic models of aspirin isomers in the condensed state

Abstract

Structural-dynamic models of aspirin are proposed on the basis of non-empirical quantum calculations of geometrical and electronic structure. In this work, the parameters of the adiabatic potential are determined, and the interpretation of the vibrational states of the compound under study is proposed. Structural-dynamic models of its isomers are constructed, the signs of their spectral identification are revealed. The conformational structure of the molecules of the substance under study was analyzed. The choice of the method and the basis for calculating the fundamental vibration frequencies and band intensities in the IR and Raman spectra are substantiated. A method for estimating anharmonic vibrations using cubic and flat force constants is described. The article presents the results of a numerical experiment; the geometrical parameters of the molecules, such as the lengths of the valence bonds and the magnitudes of the angles between them, are determined. The frequencies of the vibrational states and the magnitudes of their integrated intensities are obtained. The interpretation of isomer vibrations is given and compared with the available experimental data. General regularities in the behavior of spectral bands of different isomers are shown. Frequencies that can be used to identify the isomer from the vibrational spectra of molecules are proposed. The calculation was carried out by the DFT/B3LYP density functional quantum method. It is shown that this method can be used to model the geometrical parameters of molecules and the electronic structure of various substituted benzoic acid. It allows to construct structural-dynamic models of the specified class of compounds on the basis of numerical calculations.