E. S. Vedyaeva

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.

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.

Investigation of the structure of polymorphous modifications of fluoroalkylcyclohexanecarboxylic acids by infrared spectroscopy methods

The results of investigation of polymorphism and mesomorphic states of fluorinated derivatives of alkylcyclohexanecarboxylic acids nFACHCA and new results for n=4, 7 are discussed. The methods of vibrational spectroscopy have been used. The samples were investgiated in the 290-500 K temperature range. The spectra were recorded in the range of 400-4000 cm-1. The frequencies of normal modes and IR band intensities are calculated for conformers of H-bonded complexes with varioius orientations of fluoroalkyl radical and carboxylic group relative to the rest of the molecular compelx. The polymorphism of the nFACHCA is conformational. The influence of H-bonds on dynamics of H-bonded complex, polymorphic crystalline modification and mesophase formaiton was determined. The transitions solid crystal-liquid crystal-isotropic liquid and soution are accompanied by H-bond system reconstruction: the dimers, associates, chain associates and monomers appear.

Conformational Analysis of IR Spectra of Alkyl and Fluoroalkyl Cyclohexanecarboxylic Acids

IR spectra were simulated for a series of alkyl and fluoroalkyl cyclohexanecarboxylic acids, whose experimental spectra have been previously recorded in the temperature range 77–500 K. The simulation was performed taking into account the conformational mobility of the molecules and a decrease in the hydrogen‐bond energy of H‐complexes during heating. It has been shown that temperature‐induced changes in the spectra are caused by conformational transitions accompanied by rotation of alkyl/fluoroalkyl and or carboxyl groups and a decrease in hydroge‐bond energy 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.