G. A. Puchkovskaya

Structure and dynamics of crystal α-modification of potassium biiodate

Abstract FT-IR (4000-400 cm −1 ) and FIR (400-10 cm −1 ) spectra of α-modification of acid potassium iodate (α-KIO 3 ·HIO 3 ) were measured in the paraelectric (at 300-220 K) and ferroelectric (at 223-20 K) phases. FIR spectra of the ferroelectric phase were found to exhibit doublet structure of many bands while FT-IR spectra mainly remain invariable. The results are in good agreement with the order-disorder mechanism of ferroelectric phase transition connected with localization of the proton within a strong hydrogen bond.

IR Spectra, Polymorphism, and Intermolecular Interactions in Carboxylic Acids

This paper summarizes the results of our studies on the structural aspects of polymorphism and mesomorphous states in long-chain aliphatic compounds represented by the homologous series of alkyl-, alkoxybenzoic, and alkylcyclohexanecarboxylic acids and their completely or partially fluorinated analogs. The studies were carried out by vibrational IR spectroscopy (experiment, theory), calorimetry, polarization microscopy, and X-ray diffractometry. Conformational polymorphs have been found for the compounds, which differ in the bending of alkyl and fluoroalkyl radicals and in rotation of carboxyl groups and phenyl rings during phase transitions. Structural rearrangements and dynamic changes take place inside the nuclei of H-complexes. The dimers are partially dissociated, and open associates, chain associates, and monomers differing in their conformational composition are formed.

Conformational Mobility and Phase Transitions in Alkyloxybenzoate of Cholesterol

Abstract The structural particularities of polymorphic modifications and cholesterol liquid crystal phase have been investigated by theoretical and experimental IR spectroscopy methods. The spectra were recorded in the interval of temperatures 293–523 K within the range of 600–3600 cm−1. The frequencies of normal modes and intensities in the IR spectra have been calculated for the alkyloxybenzoate of cholesterol conformers, which may be realized under certain temperatures. Comparison of results of theoretical modelling and recorded spectra confirmed suggestion about conformational mobility basically defined with changing of steroid kennel orientation comparatively stayed part of molecule in the different phase state.

Conformational Polymorphism of Fluorinated Derivatives of Alcylcyclohexanecarboxylic Acids

Abstract The results of investigations of polymorphism and mesomorphic states of fluorinated derivatives of alkylcyclohexanecaroxylic acids nFACHCA (where n is the number of carbon atoms in the fluoroalkil radicals) and new results for n=4, 7 have been discussed. The methods of vibrational spectroscopy (experimental, theoretical modeling) have been used. The samples have been investigated in the 290–500 K temperature range. The spectra have been recoded in the range of 33–4000 cm−1. The frequencies of normal modes and intensities of bonds of IR spectra have been calculated for conformers of H-complexes with various orientations of fluoroalkyl radical and carboxylic group relative to the rest part of the molecular complex. The polymorphism of the nFACHCA is conformational. The influence of H-bonds on dynamic of H-complex, polymorphic crystalline modification and mesophase formation were determined. The transitions solid crystal- liquid crystal-isotropic liquid and solution are accompanied by H-bonds system reconstruction: the dimmers, associates, chain associates and monomers have been appeared.

Structural transformations and H-bonds in Li1-xHxIO3 mixed crystals

Abstract The lattice dynamics of pseudo-binary system LiIO 3 ·HIO 3 has been investigated by means of IR spectroscopy and NQR technique. It is shown that at compositions close to 0.2 ≤ x ≤ 0.34 mixed crystals Li 1-x H x IO 3 based on 2LiIO 3 ·HIO 3 are formed. The spectral changes observed in the 2600 and 400 cm −1 region indicate the formation of “intermolecular” hydrogen bondings between the components. The concentration phase transition to amorphous glass phase at x near 0.26 has been detected.

Conformational analysis of alkyl- and fluoroalkylcyclohexanecarboxylic acids by infrared spectroscopy methods

Modelling of IR spectra has been carried out for alkyl- and fluoroalkylcyclohexanecarboxylic acid sets, which experimental spectra in the temperature range of 77-500 K were received earlier. This modelling took into account the conformational mobility of molecules and the hydrogen bond energy decreasing in H-complexes during heating. Temperature dependent changes of spectra have been shown to be caused by conformational transitions, accompanied with turns of the alkyl (fluoroalkyl) radical or carboxylic groups and the energy decreasing of hydrogen bond during heating.

Infrared vibrational spectroscopy study of the conformational mobility of fluoroalkylbenzoic acids

Structural aspects of polymorphism are studied for homologous series of alkylbenzoic acids with a completely or partially fluorinated alkyl radical. IR absorption spectra were measured in the range 60-4000 cm−1 at 100–500 K. The spectra were interpreted by computer simulation on a PC with LEV-100 software realizing the fragmentary approach to solving the mechanical and optoelectronic problems by the method of M. V. Volkenshtein, M. A. El’yashevich, L. A. Gribov, and B. I. Stepanov. The previous assumptions that the samples possess conformational mobility and are conformationally nonhomogeneous are confirmed by comparing the spectra of the title compounds measured at different temperatures with those calculated for conformer models with different degrees of twisting of fluoroalkyl radicals and their different orientations relative to the other part of the complex.