In binary complexes of methane and ethane with HCl and LiCl, the effect of monomers orientation on C...H-Cl/ Li-Cl bonding was studied using the MP2/aug-cc-pVTZ method. Calculations predict the formation of ethane complexes with "parallel" and "perpendicular" orientation of HCl/LiCl molecules relative to the C-C covalent bond line of ethane. Decomposition of binding energy into components shows that in H-bonded complexes exchange repulsion and dispersion prevail over electrostatics and charge transfer. Stabilization of complexes with a Li-bond is mainly determined by the polarization component. Due to dispersion interactions, the perpendicular configuration of ethane complexes becomes more stable than the linear configuration.

Properties of lithium- and hydrogen-bonded complexes formed by ammonia molecules, lithium halides (LiHal, A-complexes), and hydrogen halides (ННal, B-complexes) are aligned using quantum chemical MP2/aug-cc-pVTZ calculations. NBO analysis shows energy E(2) of inter-orbital interaction between the monomers grows upon the transition to heavier and less electronegative halogen, along with an increase in the contribution from the p-orbital to the hybrid orbital of lithium atom in A-complexes and the hybrid orbital of the halogen atom in B-complexes. The calculated value of E(2) correlates to the elongation of covalent Li−Hal and Н−Hal bonds as the complex forms. Analytical investigation of the topology of electron density predicts noteworthily higher values of the electron and potential energy densities at the critical point of intermolecular contact in B-complexes, relative to A-complexes, and a growing mutual penetration of atoms that form the intermolecular contact. The higher thermodynamic stability of lithium-bonded complexes could be due to the stronger positive electrostatic potential on the lithium atoms in molecules of lithium halides and the weaker exchange repulsion of the monomers that form an A-complex.

Binary complexes with a chalcogen (A complexes) and hydrogen (B complexes) bond formed by SHX molecules (X = F, Cl, Br, OH) of divalent sulfur and a water molecule have been calculated by the MP2/aug-cc-pVTZ quantum chemical method. An NBO analysis was performed for complexes of both types along with the topological analysis of electron density and decomposition of the binding energy into components. The quantum chemical calculations showed that the binding energies, interorbital interaction energies of monomers, and electron densities at the critical point (3, –1) of intermolecular contact are close in the A and B complexes. The main contribution to stabilization of the complexes is made by the electrostatic interaction; in the B complexes, however, the contribution of the charge transfer component is also significant. The dispersion energy plays a significant role in the binding of monomers in complexes of both types. According to the calculations, the interconversion of A and B complexes occurs with a very low activation barrier.

The SPASCHARM experiment is aimed at a systematic study of the nucleon spin structure and the spin dependence of the strong interaction of antimatter and matter with matter at energies up to 45 GeV. As part of the first stage of the experiment, the study of the spin properties of hadrons will take place in a beam of negatively charged hadrons on existing beamline 14 at the operating SPASCHARM setup at the U70 facility. At the second stage, the production of polarized beams of protons and antiprotons is envisaged in beamline 24A of the U-70 accelerator facility. A polarized antiproton beam will certainly become a unique beam in the world. It is planned to measure single-spin asymmetries in dozens of reactions, both on hydrogen and on various nuclei. At the SPASCHARM facility, it is also possible to measure the transverse polarization of hyperons and elements of the spin density matrix of vector mesons. The spin structure of the nucleon will be investigated in the study of quarkonium production to determine the contribution of gluons to the proton spin. The presence of two types of polarized beams and eight types of nonpolarized beams (π ± , K ± , p , p̅ , d , C ), in combination with a polarized target, expands the range of studies of polarization phenomena and enhances the uniqueness of the project.

Using the MP2/aug-cc-pVTZ method, quantum chemical calculations of binary complexes with intermolecular C(sp 3 )...Hal−M (Hal = F, Cl, Br; M = Li, Na, Cu, Mg) bonds formed by the methide anion and its derivatives with metal halides were carried out. The calculations showed that the binding energy in the carbanion complex is higher, the greater the distance between the monomers. The least stable complexes form the strongest partially covalent intermolecular bond with the largest values of electron density at the bond (3, − 1) critical point of the C...Hal contact. The unusual properties of carbanion complexes analyzed in this study are determined by an increase in the energy of electron correlation E corr with increasing the intermolecular distance; E corr can exceed 50 kcal/mol. The MP2 and CCSD(T) levels of the theory predict a linear relationship between E corr values and binding energies. Graphical abstract Synopsis: Dramatic changes in the stability of carbanion complexes with the replacement of a hydrogen atom by lithium.

The properties of the potential function of interatomic interaction in the D−H...A triad formed by the proton donor DH and acceptor A are analyzed. The performed analysis showed that the difference in the behavior of the covalent D−H bond in complexes with conventional and nonconventional H-bonds is determined by the different sign of the potential of the proton-acceptor interaction. Quantum-chemical calculations of the ClH...OH 2 (conventional H-bond) and F 3 CH...OH 2 (nonconventional H-bond) complexes, performed by the MP2/aug-cc-pVTZ method, showed that the sign of the potential depends on the distance between the interacting monomers. In both complexes, at a large intermolecular distance, an "attractive" potential and lengthening of the D−H covalent bond are observed.

Based on NBO analysis, Bader's theory, and decomposition of the interaction energy, the unique properties of the C(sp(3))...Cl halogen bond in carbanionic complexes were revealed. In contrast to "electrostatic" complexes of hydroxyl and halide anions, in complexes of alkyl carbanions, charge transfer makes the main contribution to the binding energy. The C(sp(3))...Cl interaction is partially covalent, and the interaction energy grows very slowly with an increase in the electron density at BCP of the intermolecular contact. The nature of the halogen bonds involving the C(sp(3)) atom of alkyl carbanions is determined by the high energy of the carbon lone pair.

Quantum chemical calculations of molecular complexes formed by ammonia and methanide (electron pair donor) with HCl and ClF molecules (acceptor) at different mutual orientations are performed by the MP2 method of second-order Møller–Plesset perturbation theory using Dunning’s correlation-consistent aug-cc-pVTZ basis set, augmented by diffuse functions. An elongation in the covalent bond of the acceptor and a red shift in the corresponding IR band are observed for all complexes. NBO analysis and topological analysis of electron density are performed and maps of electron density shift upon complexation are plotted. The structure of the transition state for interconversion of NH3···HCl and NH3···ClH complexes corresponding to minima on the potential energy surface is calculated. The transition between configurations is accompanied by evolution of the intermolecular bond path with the N···H contact critical point being replaced by the critical point for the N···Cl contact. Calculated data supplemented by a comparative analysis of potential interaction curves indicate a similar nature of intermolecular binding in the H3N and HCl complexes with different orientations of monomers.

The quantum chemical calculations of the molecular complexes of ammonia and phosphine with NH3, H2O, HCl, and HF proton donors were performed by the MP2 method of the second-order Mӧller–Plesset perturbation theory with Dunning’s correlation-consistent aug-cc-pVTZ basis set augmented by diffuse functions. Complexes of two types were considered: with syn (A) and anti (B) orientation of monomers. An analysis of the nature of intermolecular interaction by various methods, including the decomposition of the binding energy into components, showed that the Y···H–X (Y = N, P; X = N, O, Cl, F) interaction in complexes of both types is a hydrogen bond. According to the calculated data, the binding energy in the B complexes is smaller than in the A complexes in accordance with the smaller calculated second-order perturbation energies \(E_{{n{\text{Y}} \to \sigma {\text{*XH}}}}^{{(2)}}\) and electron density at the critical point of the Y···H contact in the B complexes. Elongation of the X–H covalent bond of the donor and red shift of the XH band in the IR spectrum characteristic of molecular systems with an H bond were found for all the complexes.

Quantum chemical calculations at the MP2/aug-cc-pVTZ level of theory were carried out to study the molecular Y center dot center dot center dot H-X (Y = N, P; X = O, Cl, F) complexes formed by ammonia and phosphine with H2O, HCl and HF molecules with the orientation of the XH group to the backside of the N(P) lone pair (referred to as and-complexes). Various methods used for analysis identify the Y center dot center dot center dot H-X intermolecular interaction in the anti-complexes as hydrogen bonding. The NBO analysis shows that the stabilization of the ammonia and phosphine complexes is mainly determined by the n(Y) -> sigma*(XH) interaction between the acceptor lone pair and anti-sigma bond X-H of the proton donor. The values of topological parameters at the bond critical point for the H center dot center dot center dot Y contact are typical for neutral H-bonded molecular complexes; while the bridging hydrogen and acceptor atoms demonstrate mutual penetration, and all criteria concerning the integrated properties of the H atom are satisfied. The binding energy in complexes with the and-orientation of monomers calculated with the BSSE correction was found to vary in the range of 1-3 kcal/mol. The anti-complexes, like typical H-bonded syn-complexes, show lengthening of the covalent X-H bond, red-shift in the X-H stretching frequency in IR spectra, and downfield chemical shift of the bridging hydrogen atom. The inversion of the NH3(PH3) group leads to transition of the moleCular system between the anti- and syn-configurations corresponding to minima on the potential energy surface.

Quantum chemical methods were used to analyze the X-H center dot center dot center dot C interaction of the methide anion H3C-and its fluorine derivatives with H2O, NH3, CH4, and F3CH. According to quantum chemical calculations at the MP2 level of theory with the Dunning's aug-cc-pVTZ basis set, the C(sp(3)) atom of the methide anion can participate as proton acceptor in the formation of X-H center dot center dot center dot C complexes of two kinds- with syn- and anti orientation of monomers- designated as A and B complexes. Various methods of analysis, including NBO, AIM, NMR, and decomposition of binding energy, all identify the X-H center dot center dot center dot O interaction in complexes of both kinds as a true H-bond. The A and B complexes show a lengthening of the covalent X-H bond and a red shift in the X-H stretching frequency in IR spectra typical for conventional H-bonds. The performed calculations led to the conclusion that the carbon lone pair as proton acceptor can operate in both directions along the axis of the C-3v symmetry of the methide anion. (C) 2017 Elsevier B.V. All rights reserved.

Quantum chemical calculations of the HOH center dot center dot center dot CH4 complex, in which water acts as the proton donor and methane is the acceptor, were performed at different levels of theory. The NBO analysis reveals the interaction between sigma orbitals of the covalent C-H bonds of methane and sigma* antibonding orbital of the O-H bond of water associated with the charge transfer from methane to water. The values of topological parameters of the bond critical point for the H center dot center dot center dot C contact are typical for neutral H-bonded molecular complexes. The binding energy in the complex calculated at the MP2/aug-cc-pVQZ level with the BSSE correction was found to be 0.93 kcal/mol. With protonated water, the binding energy is raised up to 10 kcal/mol. In the H2OH+center dot center dot center dot CH4 complex of hydronium with methane, the O-H center dot center dot center dot sigma(C-H) interaction shows features similar to those of hydrogen bonds in the complexes of a hydronium ion with HCl and H2S molecules. (C) 2016 Elsevier B.V. All rights reserved.

Hydrogen bonded C–H···Y complexes formed by H 2 O, H 2 S molecules, hydrogen halides, and halogen-ions with methane, halogen substituted methane as well as with the C 2 H 2 and NCH molecules were studied at the MP2/aug-cc-pVDZ level. The structure of NBOs corresponding to lone pair of acceptor Y, n Y , and vacant anti-σ-bond C–H of proton donor was analyzed and estimates of second order perturbation energy Е (2) characterizing donor–acceptor n Y → σ C-H * charge-transfer interaction were obtained. Computational results for complexes of methane and its halogen substituted derivatives show that for each set of analogous structures, the Е nY→σ*C-H (2) energy tends to grow with an increase in the s-component percentage in the lone pair NBO of acceptor Y. Calculations for different C···Y distances show that the equilibrium geometries of complexes lie in the region where the E (2) energy is highest and it changes symbatically with the length of the covalent С–H bond when the R (C···Y) distance is varied. The performed analysis allows us to divide the hydrogen bonded complexes into two groups, depending on the pattern of overlapping for NBOs of the hydrogen bridge.

Quantum chemical calculations were performed at different levels of theory (SCF, DFT, MP2, and CCSD(T)) to determine the geometry and electronic structure of the HOH···CH 4 complex formed by water and methane molecules, in which water is a proton donor and methane carbon ( sp 3 ) is an acceptor. The charge distribution on the atoms of the complex was analyzed by the CHelpG method and Hirshfeld population analysis; both methods revealed the transfer of electron charge from methane to water. According to the natural bond orbital (NBO) analysis data, the charge transfer upon complexation is caused by the interaction between the σ orbital of the axial С–H bond of methane directed along the line of the O–H···C hydrogen bridge and the antibonding σ* orbital of the О–H bond of the water molecule. Topological analysis of electron density in the HOH···CH 4 complex by the AIM method showed that the parameters of the critical point of the bond between hydrogen and acceptor (carbon atom) for the O–H···C interaction are typical for Н-bonded systems (the magnitude of electron density at the critical point of the bond, the sign and value of the Laplacian). It was concluded that the intermolecular interaction in the complex can be defined as an Н bond of O–H···σ(С–H) type, whose energy was found to be 0.9 kcal/mol in MP2/aug-cc-pVQZ calculations including the basis set superposition error (BSSE).

Calculations were performed for structures of the keto and enol forms of dipeptide N-glycylglycine and its complexes with water molecules using the quantum-chemical B3LYP/6-31+G** method. The barrier for the reactions of the dipeptide’s keto-enol tautomerization that proceed by the mechanism of intramolecular proton transfer and proton transfer through water molecules connecting the oxygen and nitrogen atoms of the (-CONH-) peptide group was calculated. It was found that the barrier of the keto-enol tautomerization reaction with proton transfer by an exchange mechanism through water molecules is decreased halved compared to direct intramolecular transfer. It was shown that addition of a second water molecule in the transfer chain leads to linearization of the H-bonds bridges and increases hydrogen bonding between the peptide group and water molecules, but has virtually no influence on the calculated value of the keto-enol tautomerization barrier of about 20 kcal/mol. The structures of the transition states of the reaction indicate that the transfer of protons along the H-bonds chain is in both cases concerted but asynchronous. The order of the protons translocations along the water bridge is explained on the basis of NBO analysis of the relative strength of H-bonds in the transfer chain when the proton involved in the strongest H-bond is transferred first.

Differential equations based on the one-component harmonic model of a water chain are proposed for description of the proton wire structure with allowance for the interproton interaction of near and far neighbors. The solution to the Sturm-Liouville problem is considered for a fourth-order differential equation that takes into account interproton interactions with the first and second adjacent links of a one-dimensional chain. The function of proton displacements in such a wire is shown to describe a quasi-periodical structure, depending on the ratio of constants D-1 and D-2 for the interproton interaction of the first and second neighbors. According to calculations using the parameters characteristic of the water chain, the curve of the proton displacement is a plot of function y = cosk(1)x + sink(2)x and is similar to the curve of the hydrogen bond length distribution obtained earlier in the quantum-chemical calculations of the proton channel model.

Molecular complexes formed by different forms of carbocations (carbenium ions) and carboanions with water, acetylene, and methane molecules have been calculated by the MP2/6-311++G(2df,2pd) method. In complexes with water where the carbon atom of the carbocation (carboanion) acts as the proton donor (acceptor), the energies of the C-H⋯O and O-H⋯C hydrogen bonds turn out to be approximately the same being 13–20 kcal/mol for carbocation (carboanion) species differing in the valence state of the carbon atom. Two types of C-H⋯C interactions have been revealed depending on the charge at the bridging hydrogen atom, which is determined by the hybridization of the donor carbon atom. The C-H⋯C interaction energy in molecular complexes with the positively charged hydrogen atom (carboanion complexes with acetylene) is an order of magnitude higher than in the complexes where the bridging hydrogen atom has an excess of electron density (carbocation complexes with methane). In all the complexes under consideration, the covalent C-H bond involved in interaction is elongated, and the negative charge is transferred from the acceptor to the donor.

Quantum-chemical calculations of the geometries and electronic structures of molecules of ketenaminals 3-(diaminomethylene)-2,4-pentanedione and dimethyl-2-(diaminomethylene)-malonate and calculations of the structures of intermediates in the reaction of the nucleophilic addition of the ketenaminals to the acetonitrile molecule are performed by B3LYP/6-31+G** method. Two possible scenarios of the process are shown, depending on the mutual orientation of reacting molecules. The nucleophilic addition proceeds in two stages. It is found that the rate-limiting stage of the process is the transfer of the proton of the intramolecular hydrogen bond in a ketenaminal molecule. The experimentally observed faster reaction of pyrimidine formation for the 3-(diaminomethylene)-2,4-pentanedione molecule relative to that for dimethyl-2-(diaminomethylene)-malonate is explained by the hydrogen bond being stronger and the barrier of proton transfer from the aminogroup to the ketogroup oxygen falling upon nucleophilic attack in the former molecule.

A simple relation is found that connects the proton displacement value along the line of an H-bond X-H…Y at its formation with the proton transfer barrier to the acceptor Y. The fulfillment of the relation is verified by quantum-chemical calculations at the B3LYP/6-31+G(d, p) level of a series of H-bonded molecular complexes at different interatomic distances X…Y. With the aim to analyze the accuracy of this relation, calculations of model complexes were also performed with different basis sets. The effects of the basis set extension and electron correlation on the calculated values of the proton transfer barrier and the length of the X-H covalent bond in the molecular complex are considered. Using the suggested formalism for problems of proton transfer in H-bonded systems is discussed. A criterion of the barrierless transfer is introduced.

Quantum chemical calculations of the molecular complexes (NH3)3Zn2+...(H2O)n3...NH3 (Cn, n=11, 16, 21, and 30) that model the proton donor-aqueous chain-acceptor channel in biological molecules were performed. Periodicity of O-H bond lengths in water chains and charges of the H atoms of H-bonds observed earlier were discussed. In Cn complexes, the geometry and electronic structure of the ionic defect in the aqueous chain with an excess proton were studied. The distributions of O-H bond lengths and charges on H-bond H atoms in the region of the ionic defect obtained in ab initio (B3LYP/6-31+G**) and semiempirical (PM3) calculations are compared. The influence of aqueous chain extension, the position of the protonated water molecule, and the mobility of water molecules in the chain on the structure of the ionic defect was analyzed.