Spectral and energy characteristics of dioxybenzenes

Abstract

539.194:678.623 In the approximation for the valence force field with quantum-chemical estimation of the intensities of the absorption bands of IR spectra, calculation of the main spectral-structural and energy characteristics of dioxybenzenes is performed. This made it possible to suggest energetically more favorable conformations and assign the frequencies of normal vibrations to individual types of symmetry.Introduction. Aromatic hydrocarbons may serve as initial ingredients for obtaining a large set of compounds possessing varied physicochemical properties. Set apart is the class of oxybenzenes, which are an integral part of the vegetative world and which play an important role in redox processes including the high activity in reactions of nucleophilic and electrophilic substitution. Structural analysis of oxybenzenes, which often exist in the form of multicomponent associated mixtures, is an extremely complex problem. However, it has been little studied in the world's literature, although the compounds are widely used for obtaining substances important in practice.At the present time, the most promising in determining the structural organization of complex molecules is the spectroscopic method [1] that includes both analysis of experimental material and simulation of dynamic processes occurring in the molecule when it interacts with the quantum of an electromagnetic energy. This approach is especially effective as regards the vibrational spectroscopy, where the dynamics and kinematics can be separated with a great degree of authenticity (adiabatic approximation). Prescribing the geometric parameters of the molecule that were estimated in a certain way and solving the inverse spectral problem, one manages to obtain the intramolecular force field, which thereafter can serve as the initial one for a large number of simple models to be used as a basis for constructing real compounds.In the present work, we have made an attempt to use vibrational spectroscopy for estimating the structural features of some model systems. As the initial objects we selected phenol (C 6 H 5 OH) and its derivatives: resorcine, pyrocatechin, and hydroquinone, including their possible conformations (Fig. 1). It should be noted that the spectroscopic literature devoted to these compounds is rather broad. In [2,3], the geometric parameters of the structure of the phenol molecule are determined experimentally, and in [4][5][6][7] their optimization by the ab initio method is carried out. A series of works have been devoted to the study of the vibrational spectra of phenol and its isotopically substituted analogs [8][9][10][11][12][13][14][15]. Mainly its gas phase was studied experimentally [8,[10][11][12][13][14], and only in [9] were the IR spectra of solutions and also of phenol in a crystalline state analyzed. A similar picture is also observed in relation to the theory of the problem. In [16][17][18][19], the results of quantum-chemical calculations are presented with subsequent scaling of the obtained force fields to attain satis...

Calculation of transition intensities for torsional vibrations in IR and Raman spectra of dihydroxybenzenes

“…We can hypothesize that the pyrocatechol molecule (1,2-dihydroxybenzene) also has three stable nonequivalent isomers, which is supported by some experimental [5] and calculated [23] data. However, results of ab initio and DFT calculations, carried out in extended basis sets [11,14,20,22,24], allow us to confidently say that pyrocatechol has only two stable rotamers: an asymmetric rotamer (C s ) A and a symmetric rotamer (C 2v ) B with hydroxyl groups rotated relative to each other, where the energy of the latter is significant: E B = 1450-1630 cm -1 [11,20,22,24].…”

“…Dihydroxybenzenes, as representatives of a broad class of flexible molecules with two non-coaxial internal tops of low symmetry, having considerable practical importance [1,2], have been the subject of many spectral studies [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] and also quantum chemical calculations at different levels [8,14,[17][18][19][20][21][22][23][24][25]. Nevertheless, the problem of interpretation of the torsional IR and Raman spectra of dihydroxybenzenes in the 100-500 cm -1 region is far from resolved.…”