A MODEL OF HYDROGEN BOND FORMATION BETWEEN THE MOLECULES IN VAPOR AND LIQUID
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A MODEL OF HYDROGEN BOND FORMATION BETWEEN THE MOLECULES IN VAPOR AND LIQUID A. M. Dolgonosov1*
A model for the interaction between neutral molecules in amorphous isotropic environment is considered. The intermolecular interaction energy contains three independent groups of quantities describing non-polar forces, polar forces, and hydrogen bonds. Respectively, each of the forces is represented by its own molecular descriptor: generalized charge, dipole moment, and two numbers showing the ability of the molecule to be the donor or the acceptor of the H-bond. The H-bond contribution to the total energy of intermolecular interaction is described as a product of some quantum-mechanical threshold value and the probability of correct arrangement of interacting molecules. The accuracy of the model is verified by applying it to the estimations of the energies of dimers composed of water, alcohol, and carbon acid molecules. The accuracy and convenience of the model are evidently manifested in a priori calculations of the vaporization heat of water, alcohols, and carbon acids. DOI: 10.1134/S0022476620070069 Keywords: intermolecular interactions, hydrogen bond, adsorption, dimerization energy, heat of vaporization, generalized charge.
INTRODUCTION Based on the results of traditional quantum theory of chemical bonding claiming that hydrogen bonding (Н-bonding) is only formed in the absence of vacant orbitals, this type of bonding is commonly considered, following the ideas of Pauling [1], to be electrostatic and non-quantum in nature. Nowadays, this approach is realized in the models underlying semiempirical methods for the calculation of intermolecular interactions (IMIs). However, the assumption of non-quantum nature of hydrogen bonding not only explains the “blue” shift in the IR spectra of covalent bond vibrations in hydrides when forming a molecular complex, but also clarifies an unobservable feature of “classical” H-bonding, namely, the shift of this spectral band to the longwave region [2]. The effect of the “blue” shift is referred to as “non-classical” or “improper” hydrogen bonding [3]. Consequently, H-bonding is often understood as any IMI that is configured the way to make the hydrogen involved in this interaction. The contradiction between a special nature of hydrogen bonding and electrostatic forces in each specific system is not substantial, since these types of interaction have a common reason, i.e. the presence of hydrogen and electronegative atoms, and equal orders of magnitude. However, hydrogen bonding was also discussed in the works based on statistical analysis of empirical data in terms of electrostatic and covalent forces forming two principal components [4]. Since the model considering only dispersion and electrostatic IMIs is basically erroneous, the convenience of
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Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences, Moscow, Russia; *[email protected]. Original article submitted January 30, 2020; revised January 30, 2020; accepted February 17, 2020. 0022-4766/
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