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Liquid Crystals and their Application
Russian Journal

Zhidkie kristally i ikh prakticheskoe ispol'zovanie

Жидкие кристаллы и их практическое использование

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Zhidk. krist. ikh prakt. ispol'z. = Liq. Cryst. and their Appl., 2018, 18 (3), 14—25.
DOI: 10.18083/LCAppl.2018.3.14

Intramolecular Vibrations and Structural Nonrigidity of Different Type Hydrogen-Bonded Complexes

N. I. Giricheva1, M. S. Fedorov1, K. E. Shpilevaya2, S. A. Syrbu1, G. V. Girichev2

Author affiliations
1Ivanovo State University, 39 Ermak St.,
Ivanovo, 153025, Russia
2Ivanovo State University of Chemistry and Technology,
7 Sheremetevsky Ave., Ivanovo, 153000, Russia

The nuclear dynamics of three hydrogen-bounded complexes A···A, A···B1 and A···B2 with different structural nonrigidity (A – p-n-propyloxybenzoic acid; B1 – 4'-pyridyl 4-propyloxybenzoate, B2 – 4'-n-propyloxy-4-biphenylcarbonitrile) were analyzed.
Vibrational amplitudes of the –OCnH2n+1 substituent depend on the conformational nature and increase upon transition from the flat structure to conformations with the nonplanar structure of the carbon core. Vibrational amplitudes of terminal atoms of the –OCnH2n+1 substituent for even homologues are less than for odd homologues. Amplitudes of intramolecular vibrations of three hydrogen-bounded complexes A···A, A···B1 and A···B2 were calculated for temperatures corresponding to the crystalline and isotropic-liquid phases. The cyclic dimer of the acid A···A has the greatest rigidity and the smallest vibrational amplitudes.
For A···B1 complex, the core part enclosed between the O(–R) atoms of two molecules is dynamically rigid, however, vibration amplitudes between alkyl substituent atoms increase sharply with increasing temperature and become significant, leading to a violation of the intermolecular order in the system. The hydrogen bond strength, structure and nuclear dynamics of A···B2 complex show that the probability of its existence is small. The A-B2 system may consist of other structural units, for example, a rigid A···A dimer and two monomers B2.

Keywords: liquid crystals, p-n-propyloxybenzoic acid, 4'-pyridyl 4-propyloxybenzoate, 4'-n-propyloxy-4-biphenylcarbonitrile, quantum chemical calculations, conformers, vibration amplitudes, H-complexes, hydrogen bond, nuclear dynamics

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