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Infrared spectroscopy and gravimetry were used to study chemisorption kinetics and adsorption equilibrium in the reaction of hexamethyldisiloxane (HMDS), hexamethylcyclotrisiloxane (HMTS), octamethylcyclotetrasiloxane (OMTS), and 1,3,5 trivinyl-1,3,5-trimethylcyclotrisiloxane (MVCTS) with the surface of pyrogenic silica. It was determined that the electron-donor ability of the siloxanes in the formation of hydrogen bonds with surface hydroxyl groups decreases in the series HMDS > HMTS > OMTS > MVCTS. A reaction scheme is proposed, which includes electrophilic substitution of hydrogen of the surface silanol group in the limiting stage. It was found that the chemisorption kinetics is described by an equation of an inhomogeneous-surface model with allowance for interaction between species in a neutral-field approximation. The relative reactivity of the siloxanes in these transformations is governed mainly by the difference of the energies of the reactant siloxane bonds.

MINDO/3 calculations have been made on the potential-energy surfaces for the attachment of OH. radicals to benzene (1) and naphthalene (2) in the vapor state. The activation energies of these reactions are calculated as 88 and 58 kJ/mole. while the enthalpies at 298K are calculated as -211 and -199 kJ/mol. The transition states in (1) and (2) lie closer to the reagents than the products on the reaction coordinate, while (1) has an earlier transition state than does (2). The transition states in these reactions have high dipole moments: 3.1 and 3.6 D, respectively, which are due to charge transfer from the hydrocarbons to the OH.. Quantum-chemical calculations and kinetic data on the reactions of aromatic hydrocarbons with OH. in aqueous solution indicate that the mechanism is probably not one involving electron transfer and a rate-limiting stage in the attachment. These processes are of high performance because the radicals are of high stability, while polar effects determine the selectivity.

The calculation of the rate constants for the processes in the reduction of diazonium, tropylium, verdazylium, and pyrylium cations by various organic electron donors, using the equations of the Marcus theory with allowance for the reorganization energy of only the outer coordination sphere, leads to values which are one to seven orders of magnitude higher than the experimental values. By quantum-chemical calculations it was shown that the reduction of diazonium and tropylium cations to the corresponding radicals is accompanied by a substantial change in the structure of the reagents. This leads to high values for the reorganization energy of the inner coordination sphere of the cations, which must be taken into account during calculation of the rate constants. The differences in the rate constants of the processes of direct electron transfer from the electron donors to the organic cations and the recombination of these reagents depend on the dissociation energy of the bond of the cation with the donor leading to the electron transfer products.

MINDO/3 has been applied to the effects of field strength and direction on elementary stages in electroorganic reaction, the electrochemical reduction of methyl chloride: molecule and anion-radical orientation, electron transfer from electrode to molecule, anion radical dissociation, and methyl radical and anion inversion. The molecular electronic and stearic structures are affected by the field, as are those for the anion radical, the molecular and radical reorientation barriers, the direction and height in the radical dissociation barrier, and the radical and anion configuration stabilities. An explanation is given for the electrolysis data for alkyl halides and for the properties of chemically modified electrodes.

It has been found that the reduction of substituted diazonium, iodonium, and tropylium salts by cation radicals of tetra-tert-butyl-bis-pyrylium, tetramethyl-p-phenylene diamine (I), tetraphenylbenzidine, and N-methylphenothiazine obey the kinetic equation of the second order and that it follows an electron transfer mechanism. The logarithms of the rate constants of these reactions decrease with increasing standard free energy of the electron transfer reaction. The rate of the reaction of C6H5N2+ BF4- with I and the selectivity of the reactions of the substituted diazonium salts with I increases with the electron donor capacity of the solvent. The addition of crown-ethers accelerates the reaction. The reaction rate increases also with increasing ionic strength of the solution, whereby the Cl- anions have a specifically accelerating effect. The observed rules governing the influence of the medium contradict those found earlier for the interaction of organic cations with neutral radicals and anion radicals. This is attributed to the fact that the electron transfer takes place in ternary complexes cation-solvent (crown ether, Cl- ion)-cation radical.

¹H NMR spectroscopy of adsorbed water was used to study mesoporous silica gel and carbosils synthesized with carbon in the range from 4 to 14.5% w/w in the surface layer. It has been revealed that both silica gel and carbosil are characterized by a rise in temperature of water freezing in an aqueous medium in mesopores. This phenomenon may be explained by contact of water adsorbed in pores with a continuous aqueous medium. The changes in free energy of water in pores due to adsorption have been calculated. It has been shown that carbonization of the mesopore silica gel surface leads to formation of carbon layers which are denser than those on a nonporous silica and the main types of water adsorption sites on the surface are basic graphite planes of carbon and oxygen-containing groups on the carbon part of the carbosil surface.

The application of several physicochemical parameters of organic compound structures for description of their nonspecific and specific interactions at adsorption on the oxide surface as well as for chemisorption kinetics in these systems is discussed. An approach to calculate the distribution functions on the coefficients of linear equations, connecting the adsorption or chemisorption parameters on the heterogeneous surface with physicochemical parameters of adsorbates or reagents, is presented. It has been used for the description of some adsorption equilibria and chemisorption kinetics of organosilicon compounds on the SiO2 surfaces and for determination of the dispersive and specific components of the free surface energy of Si, Ti, and Al oxides.

A kinetic model including the surface distributions of both radiative and nonradiative (bimolecular) rate constants has been proposed for explanation of bimodal distribution curves of apparent rate constants of bimolecular pyrene fluorescence quenching by N,N-dimethylaniline on a nonporous silica surface. Assuming that the distributions of radiative and nonradiative rate constants are uniform functions, the analytic solutions of the generalized integral equation for the decay profile and average lifetime of the fluorophore excited state have been derived. The average values and mean-square deviations for both distributions have been determined for the bimolecular pyrene fluorescence quenching on the silica surface. The proposed model may be used as a basis for detailed studies of regularities in bimolecular photoreactions on the heterogeneous solid surface.

Several methods (condensation approximation, regularization, and non-negative least-squares (NNLS)) have been applied for calculating the pore size distribution (PSD) function from simulated isotherms. It has been shown that two near by peaks in the low size region may be recovered well by both regularization and NNLS method only for isotherms without experimental error. Wide peaks may be recovered by numerical methods almost independently on a number of experimental points and error inherent in input data. Condensation approximation is the most insensitive to the experimental errors. However it gives a distorted one peak distribution shifted to low values of micropore size and having a long tail at large values. In the case of isotherms with large errors (10% for regularization and 5% for NNLS), both numerical methods give PSD functions close to that obtained by the CA method.

The influence of distance between OH groups and lattice disorder of silica surface on the peak characteristics in the TPD (temperature programmed desorption) spectra of water desorption as well as on the coverage dependence of desorption activation energy has been investigated by the Monte Carlo simulation. The experimental TPD spectra of water desorption from different silica samples and coverage dependencies of desorption activation energy have been compared. The BOC-MP approach has been used to calculate the activation energies for possible associative desorption reactions which are realized during the dehydroxylation. It was established that most activation energies for associative desorption lie in the same region as those estimated from the TPD spectra.

The effect of the catalyst concentration (Ca(II)), the method of deposition on the carbon surface and burn-off on the parameters of the micropore and mesopore size distributions have been established. Modification of the carbon by steam and in the presence of impregnated Ca(II) changes both the microporous and mesoporous carbon structure. The micropore adsorption capacity decreased and the mesopore surface area and the average and the variance of the half-width of the micropore slits increased with increasing burn-off for all of the carbons that were studied. The sensitivity of the parameters that were used for characterizing the porous structure of the activated carbon to the changes in the burn-off is determined by the structure of the raw materials. The greatest effect on the porous structure was exhibited by the activated carbons that were prepared from plum stones and charcoal, while the least change was demonstrated by the activated carbons that were prepared from coking and hard coal. The most appropriate method of catalyst deposition on the surface of the activated carbon is calcium ion exchange compared to the impregnation method for deposition.

The MINDO/3 method was used to study the effect of intensity and vector direction of the external electric field on activation barriers of unimolecular reactions which are possible in electrochemical transformations of simple organic compounds:  orientation of molecules and radical anions, heterogeneous electron transfer to adsorbed molecules, dissociation of radical anions, cations, and molecules, inversion of anions, free radicals, and neutral molecules, cis−trans isomerization, and chair−boat conformational transition in molecules. The electronic and spatial structure of the molecules, free radicals, and ions, the height of the activation barriers of their reorientation, dissociation, isomerization, and conformational transition, and the configurational stability to change as affected by the field in the range 0.01−0.05 au are determined. Obtained data permit one to theoretically ground different effects under organic compound adsorption on the electrode surface, changes in stereochemistry of the products of alkyl halide electroreduction, and some properties of chemically modified electrodes possibly affected by electrode potential gradient.

Quantum chemical computations of potential energy surface sections along the reaction pathway for interaction of some molecules with silica surface OH groups in a cluster approach have been performed. Two minimums on the potential curves which are due to formation of linear hydrogen-bonded and following cyclic donor−acceptor complexes were observed prior to formation of the transition state for proton transfer in the cyclic complexes. Some tendencies between quantum chemical indexes of organic molecules and heats of the complex formation or chemisorption activation energies on the silica surface have been established.

The approximate analytical solutions for integral equations including γ distribution on the chemisorption rate constant as well as γ, normal, or uniform distribution functions on the distance between neighboring sites, taking into account the lateral interaction between chemisorbed species in mean-field approximation, for kinetic isotherms on an amorphous random and patchwise heterogeneous solid surface have been obtained. Influence of parameters of these functions on the shape of simulated kinetic isotherms and on the moments of distribution on observable rate constants have been studied. Satisfactory agreement between the present model predictions and experimental kinetic isotherms obtained for the chemisorption of organosilicon compound on the surface of pyrogenic silica has been found.

It was shown that the rate and selectivity of irreversible processes of electrochemical and chemical reduction of onium cations of elements of groups V-VII, containing alkyl and aryl substituents, increase with increasing principal quantum number of the central atom of the cation. This pattern is explained on the basis of the Marcus theory by a decrease in the energy of heterolytic dissociation of the bonds of the substituent to the central atom of the cation, leading to a decrease in the free energy and energy of reorganization of the reaction, as well as to an increase in their rate and selectivity.

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