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The electron density distribution in [Re₄Q₄X₁₂]^4- cubane-like clusters (Q = S, Se, Te; X = F, CN) was investigated by the AIM and ELF topological quantum-chemical methods. The Re-Re, Re-Q, and Re-X interatomic interactions are characterized by bcp type critical binding points and are strained.

The profile of the reaction СН₃ОН + МОН → СН₃ОМ + Н₂О in the presence of an alkali (МОН, М = Li, Na, K) was investigated by the ab initio quantum-chemical method for the gas phase (with allowance for the solvent) within the continuum model. The proton transfer and the formation of the alkaline methoxide molecule in МОН/DMSO/СН₃ОН systems (М = Li, Na, K) in the alkali-methanol pre-reaction complexes can take place without their preliminary dissociation and are barrier-free reactions.

The parameters of the geometrical configuration of octachlorotrisilane Si₃Cl₈ were determined by quantum-chemical and gas-phase electron diffraction methods at 303±2 K. The calculated barrier to the internal rotation of SiCl₃ groups relative to the Si-Si bond was calculated.

The geometrical structure, force fields, and vibrational spectra of CeX₄ (X = F, Cl, Br, I) were investigated by second, third, and fourth order Möller-Plesset perturbation theory, CISD+Q configuration interaction method, and the CCSD(T) coupled cluster method. Calculations on CeF₄ were also performed by multiconfiguration second order perturbation theory MCQDPT2/CASSCF. The wave function of the ground state of CeX₄ molecules was found to be appreciably non-one-configurational; this property increases from cerium fluorides to iodides and leads to the divergence of the series of Möller-Plesset perturbation theory. The calculated data point to a tetrahedral equilibrium nuclear configuration in CeX₄ molecules. The energy barriers to the inversion of the tetrahedral CeX₄ molecules via the square configurations are high enough, 74-89 kJ/mol. The calculated vibration frequencies, effective internuclear distances, and mean amplitudes of nuclear vibrations in CeF₄ agree with IR and Raman spectroscopic and high-temperature gas-phase electron diffraction data.

A theoretical study of the interaction between N–nitrosodiethanolamine (NDELA) molecule and one to five molecules of water has been performed at the B3LYP level using a large polarized basis set. The calculated complexation energies (corrected for BSSE and ZPVE)
of NDELA with one, two, three, four and five molecules of water are –4.62, –9.83, –15.29, –21.60, and –25.10 kcal/mol respectively at the B3LYP/6–311++G** level. In all complexes studied there are red shifts in the vibrational frequencies of the O–Hs of NDELA and water molecules along with increases in the corresponding IR intensities.

The IR spectra of L- and DL-serines HN-CH(CH₂OH)-COO^- (without diluents) were investigated in the temperature range 93-413 K; the changes in the IR spectra due to temperature variations were correlated with previously obtained diffraction data on anisotropic compression of structure and changes in the geometrical parameters of the hydrogen bonds.

The microwave spectrum of 5-methyl-1,3-dioxane was studied in the frequency range 12-35 GHz. The а and с type rotation transitions with J ≤ 30 were identified. The rotational constants А =
4658.5244(33) MHz, В = 2383.3930(12) MHz, and С = 1724.28907(88) MHz and the quartic constants of the centrifugal distortion of the molecule in the ground vibrational state were determined. The components of the dipole moment were found, μ_а = 1.76 ± 0.01 D and μ_с = 1.10 ± 0.01 D; the net dipole moment of the molecule is μ = 2.08 ± 0.01 D. 5-Methyl-1,3-dioxane was calculated by the B3PW91/aug-cc-pVDZ density functional theory method. The calculated data are compared with the experimental data. The most stable conformation is the chair conformation with an equatorial orientation of the methyl group.

The spatial isomers of the new synthetic analogs of ethyl permithrinic ether and permethrin were investigated by NMR (¹Н, ¹³С, DEPT (distortionless enhancement by polarization transfer), COSY (correlation spectroscopy), CHCORR (heteronuclear (C, H) shift correlation spectroscopy), ROESY (rotating-frame Overhauser effect spectroscopy)). Several tendencies were revealed in the ¹Н and ¹³С chemical shifts of the α atoms of the substituents in the 2nd and 3rd positions of the cyclopropane ring. For substituents cis-orientated relative to the ester group, the spectra show a paramagnetic shift of the ¹Н signals and the diamagnetic shift of the ¹³С signals relative to the trans-orientated substituents. The ¹Н and ¹³С chemical shifts of the α atoms of the substituents in the 2nd and 3rd positions of the cyclopropane ring permit an unambiguous determination of the stereochemistry of ethyl permethrinic ether and permethrin analogs.

The antisymmetry of proton configurations was studied for the hexagonal water rings with different conformations. The change in the direction of all hydrogen bonds was used as an additional symmetry operation. The ring configuration energies were calculated using the intermolecular interaction potentials. For different ring conformations, the relationships between antisymmetry and energy were analyzed and compared.