Using the DFT/B3LYP method with the basis sets 6-31G * ( * * ), we analyzed the vibrational spectra of nitrobenzene and nitropyridines for free molecules and their solutions in water, ethanol, and benzene. The influence of a solvent on the behavior of the characteristic spectral parameters of nitrobenzene is revealed, and the assignment of vibrations for nitropyridines is given.Introduction. Nitro-substituted compounds of benzene and pyridine rank among the organic compounds that can be used in heterogeneous systems employed to create laser elements in quantum electronics [1].Oscillation spectroscopy is a very effective method of studying the structure of such systems. For example, in studying the nitrobenzene-molecular sieve system by the IR spectroscopy method [2], from the position and form of the spectrum bands inferences were draw as to the possible mechanism of interaction of nitrobenzene with the active centers of alumosilicate sieves of the MSM-41 type. Here, as a theoretical basis for such an analysis, the assignment of the fundamental vibration frequencies for nitrobenzene that was proposed in [3, 4] is used. However, this assignment is incomplete and disagrees with the results of [5,6], where a detailed experimental investigation of the IR and Raman spectra of nitrobenzene and of its deutero-and isotope-substituted compounds was made. To theoretically analyze vibrational spectra, the authors of [5,6] invoked the classical scheme [7,8] of the extension of a force field from compounds that are akin in electronic structure.It should be noted that the same scheme was employed in [9] for a theoretical analysis of the vibrational spectrum and force field of nitropyridines. A preliminary stage of the analysis indicated was the theoretical investigation of the vibrational spectra of nitrobenzene, and to this end the same experimental evidence was invoked that was referred to by the authors of [5,6]. However, the assignments proposed in [5, 6] and [9] are different for the vibrations pertaining to the nitro group. One possible way out of the situation is by invoking direct methods of calculating the electronic structure, force fields, and vibrational spectra of the nitro-substituted, six-term aromatic compounds. Such are the ab initio methods of the quantum mechanics of molecules [10].The aim of the present work is to construct structural dynamic models of nitrobenzene and nitropyridines and to analyze the behavior of the vibrational spectra of these compounds in different media.Theoretical Analysis of the Vibrational Spectra of Nitrobenzene and Nitropyridines in the Harmonic Approximation. The quantum calculations of the molecules of nitrobenzene and α-, β-, and γ-nitropyridines are brought about by the DFT/B3LYP method with the basis sets 6-31G * ( * * ). We succeeded in describing the torsional vibration of the nitro group by assuming the plane structure of molecules (C 2ν symmetry for nitrobenzene and γ-nitropyridine and C s symmetry for α-and β-nitropyridines).To compare the assignments and analyze the be...

Based on ab initio quantum calculations of the electronic structure for different conformers of V and V x gases, we propose an assignment of the fundamental vibrational states of the compounds.Key words: electronic structure, adiabatic potential, vibrational state, conformers of V gas, molecular modeling.Introduction. V and V x gases (dimethylaminoethyl mercaptoethyl phosphonate) are highly toxic organophosphorus compounds posing an environmental threat. Identification of the indicated compounds from optical spectra is directly connected with model calculations of their geometric structure and vibrational spectra. The predictive possibilities for vibrational spectroscopy rest on ab initio methods for estimating the parameters of the adiabatic potential, determining the physicochemical properties of molecular compounds, including the position and intensity of bands in the optical spectra of polyatomic molecules.Establishing the correlation between the chemical structure and the optical spectrum of a molecular system in a specific phase state makes it possible to identify the individual molecular fragments of complicated analyte compounds. It is sufficient to refer to monographs [1][2][3]. In [4], the problem was discussed in detail for a number of organophosphorus compounds. In [5], the described possibilities of vibrational spectroscopy are applied to constructing structural dynamic models for known organophosphorus compounds: sarin, soman, tabun, and cyclosarin.For V and V x gases, available experimental data on the vibrational spectra are extremely limited [6]. However, the individual fragments of the compounds, such as paraffin hydrocarbons, have been well studied by vibrational spectroscopy methods [1]. Data on the vibrational spectra of phosphorus-, sulfur-, and nitrogen-containing fragments from monograph [1] also can be used to assess the results of a numerical experiment, along with the experimental data presented in [5].The presence of a large number of hydrogen atoms in the considered compounds requires estimation of the effect of anharmonic resonances when the numerical calculations are carried out. This is feasible with modern software, such as in [7].Results of Model Calculations and Discussion. The vibrational spectra were calculated in the anharmonic approximation of the theory of molecular vibrations. We gave preference to the ab initio quantum method DFT/B3LYP with basis sets from 6-31G*(**) to 6-311G*(**) [7].To solve the anharmonic vibrational problem in second-order perturbation theory, we used the model Hamiltonian [8]

We have used direct quantum DFT methods to calculate the parameters of the adiabatic potential of four benzophenone conformers. According to the data obtained, the existence of only one conformer is possible (C 1 symmetry) for the free benzophenone molecule, for which torsional vibrations of the benzene moieties are reproduced and for which we calculated the vibrational spectrum in the anharmonic approximation of the theory of molecular vibrations.Key words: assignment of benzophenone vibrations, anharmonic resonance effects.Introduction. Benzophenone (diphenyl ketone: two benzene rings replace the methyl groups in the acetone molecule CO(CH 3 ) 2 ) is an aromatic ketone. It has a number of physical properties making it attractive for practical purposes. This especially involves a substantial piezoelectric effect, the ability to efficiently transfer excitation energy. So establishing a connection between the structure and spectra of benzophenone conformers in different phase states has not lost its timeliness. It is sufficient to refer to the review in [1], in which the spatial structure and electronic structure were calculated for the planar and twist conformers of benzophenone in the harmonic approximation of the theory of molecular vibrations [2]. To do this, the most promising of the many ab initio quantum methods was used: DFT/B3LIP/6-31G * [3]. However, benzophenone also allows for other spatial conformations, and the presence of a large number of hydrogen atoms requires analysis of the vibrational states of the molecule in the anharmonic approximation [4]. The same situation occurs for methyl-substituted and amino-substituted benzophenone. For example, in [5,6] agreement between calculated and experimental data was achieved with respect to the frequencies of the fundamental vibrations, using different schemes for the scaling procedure [7]. Thus the following question remains: does the procedure involve scaling by compensating for deficiencies of the density functional method DFT/B3LIP/6-31G * in calculating the fundamental vibrational states, or is this a method for taking into account the anharmonicity of the vibrations? For this purpose, we need to carry out calculations of the adiabatic potential for the studied compounds in the anharmonic approximation. In [1][2][3][4][5][6][7], all the calculations were performed in the harmonic approximation.In this paper, we present the results of model calculations of the adiabatic potential and the vibrational spectra for four conformers of benzophenone. The first two (C 2v symmetry) have already been mentioned. The remaining two were obtained from a planar model by rotation of one ring by the angles π/2 (C s symmetry) and π/4 (C 1 symmetry) about the C 1 -C 3 bond (the atoms in the molecule are numbered as follows: ring 1, C 3 C 4 C 5 C 6 C 7 C 8 ; ring 2, C 14 C 15 C 16 C 17 C 18 C 19; carbonyl group C 1 O 2 ; bridge C 1 C 3 -C 1 C 14 ).Discussion of Results. Detailed data on the geometric parameters for all the considered conformers of benzophenone are given in...

На основании квантовых расчетов параметров адиабатического потенциала ряда замещенных 5Х урацила (X = CH 3 , NH 2 , F, Cl) построена теория характеристических колебаний для мономеров и димеров данного класса биомолекул. Выявлены признаки спектральной идентификации для димеров с cильной водородной связью. Ключевые слова: колебательные спектры, димеры 5Х-за мещенных урацила, параметры адиабатического потенциала.

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