IR absorption spectra and structure of 4-cyano-4′,-p-alkoxybiphenyls

The IR absorption spectra of 4-cyano-4,-p-alkoxybiphenyls were investigated experimentally (in the range 100–3200 cm^–1 at 100–400 K), and they were interpreted on the basis of a calculation of the frequencies, forms, and intensities of the normal vibrations of various conformers of the propyloxycyanobiphenyl molecule. Temperature and phase changes in the parameters of the IR spectrum are explained by a change in the conformational composition and intermolecular interactions in the investigated liquid crystals.Institute of Physics, Ukrainian Academy of Sciences. Saratov State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 2, pp. 105–111, January–February, 1993.     

The effect of the hydrogen bonds on the molecule conformation in 2-biphenylmethanol

Infrared spectra of hydrogen-bonded organic compound 2-biphenylmethanol has been studied in the wide temperature range from 320 to 12 K. It has been found that IR spectra drastically changed with temperature in the 700–850, 1290–1500, and 3100–3600 cm⁻¹ spectral regions, where deformational vibrations of phenyl rings and methanol group, as well as ν(OH) stretching vibration manifest themselves. The analysis of the computer simulation of the IR spectra for various 2-biphenylmethanol conformers, which are characterized by different combinations of angles of the mutual orientation of the phenyl rings relative to each other and a methanol group relative to the phenyl ring allowed us to conclude that the hydrogen bonding results not only in the shortened of the intermolecular bonds, but also in the increasing of the angle between phenyl ring and methanol group. In other words, hydrogen bonding leads to the changes in the molecule conformation.     

Hydrogen bond and the structures of 2-, 3-and 4-biphenylmethanols

Density functional theory (B3LYP/6-31G*) is applied to calculate structures, energy, dipole moment, polarizability, frequencies of normal vibrations in the harmonic approximation and intensities in vibrational spectra of 2-, 3-, and 4-biphenylmethanol molecules and their H-complexes that can form in crystalline, amorphous, and liquid phases. Based on the analysis of simulation results, the effect of the position of a methanol group in the molecule on its vibrational spectrum is discussed. The structure forming role of a hydrogen bonds in biphenylmethanols and the possibility of realization of two polymorphic modifications in 2-biphenylmethanol are stated. These modifications are: metastable monoclinic, in which each of four molecules of the unit cell is a link of a chain H-associate; and stable triclinic, in which four molecules of the unit cell organize an H-complex in the form of a cyclic tetramer. It is found that crystalline samples of 3-and 4-biphenylmethanols consist of chain H-associates. A glass-like sample of 2BPhM being a mixture of H-complexes consisting of cyclic tetramers and chain associates contains crystalline nuclei of triclinic and monoclinic polymorphous modifications in the supercooled state. In a liquid sample of 2BPhm, chain H-associates and free molecules are realized.     

IR spectra temperature changes and conformational structure of 4-butyl-4′-cyanobiphenyl

IR spectra of 4-butyl-4′-cyanobiphenyl in the liquid and solid-crystal states were measured in the 400–4000 cm^–1 region at 28–70°C. Changes of the spectra as a function of temperature are due to the conformational fluxionality of the molecules according to calculated IR spectra of the possible 4-butyl-4′-cyanobiphenyl conformers. Calculations were carried out using the method of fragments and the LEV-100 program package. Bands sensitive to the conformational changes in the molecular structure were found. IR spectra have been interpreted. Conclusions have been made about the conformations of the sample in the solid-crystal and liquid phases. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 325–333, May–June, 2009.     

Novel diphenylsulfimide antioxidants containing 2,6-di-<Emphasis Type="Italic">tert</Emphasis>-butylphenol moieties

New diphenylsulfimide derivatives containing substituents with the 2,6-di-tert-butylphenol moiety at the nitrogen atom were synthesized. Their molecular structures were established by X-ray diffraction. Antioxidant activity was experimentally evaluated by spectrophotometry based on hydrogen transfer to the stable radicals, namely, 2,2-diphenyl-1-picrylhydrazyl and the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cation (ABTS^·+), and using in vitro lipid peroxidation in rat brain and liver homogenates. The presence of phenol and diphenylsulfimide moieties in one molecule leads to a significant enhancement of antioxidant activity. The new compounds exhibit moderate inhibitory activity against enzymes involved in carbohydrate and lipid metabolism. The evaluation of antiglycation activity showed that the new sulfimides taken at a concentration of 100 μmol L^–1 have activity comparable with that of aminoguanidine.     

Peculiarities of the structure and intermolecular interactons in 4-n-ALKYL-4′-cyanobiphenyls studied by IR spectroscopy

Experimental and theoretical methods of IR spectroscopy have been used to study the peculiarities of the structure and of intermolecular interactions in the homologous series of 4-n-alkyl-4′-cyanobiphenyls (abbreviated to nCBs, where n is the number of carbon atoms in the alkyl radical). IR absorption spectra of nCBs (n = 4, 8, 9) were measured in the frequency range from 400 cm^?1 to 4000 cm^?1 and in the temperature range from 26° to 100°C, which corresponded to the crystalline, liquid crystalline and liquid states of the samples. The analysis of the measured spectra was performed with regard to available X-ray data on the structures of crystalline phases and to the theoretical modeling of IR spectra; a comparison with previously studied spectra of nCBs with n = 2 and 5 was made. Characteristic differences between the spectra of higher and lower homologues of nCBs were found. Changes in the conformation of nCB molecules with the change of temperature and the length of the alkyl radical are discussed.     

Vibrational spectra and the structure of long-chain aliphatic compounds

Polymorphism and the structure of mesomorphous states of long-chain aliphatic compounds (LAC) have been studied by vibrational spectroscopy (theory, experiment) using calorimetry, polarizing microscopy (PM), and X-ray diffraction (XRD) analysis as auxiliary methods. LAC are represented by homologous series of alkyl- and alkoxybenzoic acids, alkylcyclohexanecarboxylic acids, their completely or partially fluoroalkyl-substituted analogs, and 4-cyano-4′-(n-alkoxy)biphenyls. The studies were performed at 77–500 K. IR absorption and Raman spectra were measured at 30–4000 cm⁻¹. The compounds are characterized by conformational polymorphism. The molecules and their H-complexes undergo structural rearrangements during phase and conformational transitions. In the course of the rearrangements, alkyl and fluoroalkyl radicals (AR and FAR) are twisted, and carboxyl groups are disordered. The rearrangements dictate the structure of mesophases, which are mostly formed of H-complexes consisting of dimers, monomers, and open associates. N. G. Chernyshevskii Saratov State University. Institute of Physics, Ukrainian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 338–344, March–April, 1995. Translated by L. Smolina     

Structure and Conformational Mobility of 4′‐Pentyl‐4‐Cyanobiphenyl from IR Spectroscopic Data

The structure and conformational mobility of 4pentyl4cyanobiphenyl in the liquid and liquidcrystal states were investigated by means of IR spectroscopy (experiment and theory). IR absorption spectra in the frequency range 400–4000 cm^-1 were measured in the temperature range 26–150°. Theoretical simulation of the IR spectra was performed using the fragment approach. A comparison of theoretical and experimental spectra showed that the examined samples were mixtures of conformers; characteristics of the most probable conformers are given. Temperaturerelated changes in the spectrum are due to the conformational mobility of the molecules, which is not high in the temperature range considered.