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Raman spectra of ethylene glycol (EG) and 1,3-propylene glycol (1,3-PG) aqueous solutions with the diol content from 10 to 90 mol% were measured. The diol content weakly influences the EG and 1,3-PG Raman bands in the spectra of the solutions in the region 250-1800 cm

Raman spectra of liquid ethylene glycol (EG), 1,2-propylene glycol (1,2-PG) and 1,3-propylene glycol (1,3-PG) were analyzed in terms of the conformational composition of the molecules. The analysis was based on comparison of the experimental spectra with the results of the density functional theory (DFT) calculations of the structure, energy and Raman spectra for 10 conformations of EG molecule, 27 conformations of 1,2-PG molecule and 25 conformations of 1,3-PG molecule. The gas-phase approximation calculations well describe the main features of the experimental spectra of the liquid substances in the region 600 – 1600 cm−1. Calculations for clusters of EG molecules showed that an increase in the number of molecules in a cluster leads to significant improvement of the agreement between the calculated and experimental spectra. The conformations of molecules in the clusters are strongly distorted in comparison with the results of the gas-phase approximation. Thus, the intermolecular interactions influence significantly the conformational order and the Raman spectra of the diols.

We carried out calculations of non-resonance Raman spectra of s-carotene and polyenes CH2 (CH CH )n-2CH CH2 using the density functional theory (DFT). We revealed that the peak positions and intensities of the C C and C C stretching bands depend on length of the polyene chain and type of the isomer. Our experimental non-resonance Raman spectra of s-carotene powder match well the DFT-simulated Raman spectrum of s-carotene in the all-trans form. The peak positions and relative intensities of the C C and C C stretching bands of s-carotene turned out to be similar in the resonance and non-resonance Raman spectra. An increase in the number of conjugated double bonds (n = 3–30) in a polyene structure results in a monotonous shift of the positions of the most intense C C and C C bands towards lower wavenumbers with an increase in the band intensities. An increase in the isomer number results in the monotonous decrease of the C C stretching band intensity for polyenes with 9, 10, 11, 15 and 24 double bonds. An increase in the isomer number inhomogeneously influences the form, position and intensity of the C C stretching band.

Experimental Raman spectra of liquid and solid polyethylene glycols (PEGs) with various molecular weights were compared with the results of the density functional theory (DFT) calculations. The structure, energies and Raman spectra of molecules in the trans and 72 helical conformations with various orientations of the terminal groups were calculated for PEG molecule with 9 monomer units. Recorded spectrum of PEG with the average molecular weight of 400 Da (8–9 monomer units) matches very well the calculated spectrum of the most thermodynamically stable g’G(TTG)8g’ conformation. DFT-calculated Raman spectra for the g’G(TTG)ng’ conformation depend on the amount of the monomer units in PEG molecule. The peak position of the PEG Raman line at about 1100 cm−1 can be used to estimate the molecular weight distribution of short molecules.

Binuclear hydride centers containing two Zr(IV) atoms are suggested as promising catalysts for the hydrogenolysis of alkanes under mild conditions (T < 450 K, p ∼ 1 atm). Reactions of model compounds L2(H)Zr(X)2Zr(H)L2 (X = H, L = OSi≡ (4a), X = L = OMe (4d)), L(H)Zr(O)2Zr(H)L (L = OSi≡ (4b), Cp(4c)) and (≡SiO)2(H)Zr-O-Zr(H)(OSi≡)2 (4e and 4f) with the propane molecule were studied using the density functional theory method. The results show that centers of the 4a, 4e, and 4f types and especially 4b are promising catalysts of the hydrogenolysis of alkanes due to a high degree of unsaturation of two Zr atoms and their sequential participation in the splitting of the C-C bond and hydrogenation of ethylene formed as a result of splitting.

The paper is a review of a series of publications devoted to a number of homogeneous and heterogeneous catalytic reactions, their mechanisms, and energy characteristics. These reactions are promoted by coordination unsaturated compounds of Ti and Zr and proceed with cleavage and/or formation of C-C and C-H bonds in the hydrocarbon chain (polymerization reaction of ethylene, styrene, and butadiene-1,3, hydrogenolysis and hydroisomerization of linear and branched alkanes, and H/D isotope exchange in alkanes). A high-level quantum chemical method (DFT, PBE functional, gauss type TZ2p basis sets, the original PRIRODA program) was applied for the catalytic systems under the study. The nature and the structure of the active center, detailed mechanisms, and energy profile of the reaction of the substrate with a catalytic particle are considered. We compare our data with the results of both experimental and theoretical contributions from other authors.

The acid-catalyzed cyclization of 1-(3,4-dialkylaryl)-3-chloropropan-1-ones to dialkylindanones via the intermediate formation of (3,4-dialkylaryl)propenones was studied. This reaction affords isomeric products: 5,6-dialkylindan-1-ones and 4,5-dialkylindan-1-ones. The DFT quantum chemical calculation results correlate with the experimental data and suggest that the structural factors affect the ratio of products.

Density functional theory was used to study model ethylene reactions with CpTiIIIEt+A− (A− = CH3B(C6F5)3−, or B(C6F5)4−; A− can be absent) compounds. The polymerization of ethylene on an isolated CpTiEt+ cation is hindered because of equilibrium between the CpTi(C2H4)Et+ primary complex and the primary product of CpTiBu+ insertion. At the same time, the polymerization of ethylene on CpTiEt+A− ion pairs (A− = CH3B(C6F5)3− or B(C6F5)4−) is thermodynamically allowed (ΔE from −26.2 to −25.6 kcal/mol and ΔG298 from −10.9 to −10.4 kcal/mol) and is not related to overcoming substantial energy barriers (ΔE# = 8.2−12.3 kcal/mol and ΔG298≠) = 7.8−13.3 kcal/mol). The degree of polymerization can be low because of the effective occurrence of polymer chain termination by hydrogen transfer from the polymer chain to the monomer.

The model reactions of neopentane hydrogenolysis and hydroisomerization on transition metal hydrides (≡ Si−O)3MIVH (1), (=eqSi−O)2MIVH2 (2), and (≡Si−O)2MIIIH (3) (M = Zr, Ti) immobilized on the surface of silica were studied by density functional theory. It was shown that the hydrogenolysis of neopentane could occur on all the three types of metal hydrides, the catalytic activity of reaction centers increasing along the series M(IV) monohydrides 1 < M(IV) dihydrides 2 < M(III) hydrides 3. At the same time, the isomerization of the hydrocarbon skeleton of neopentane observed experimentally on titanium-based systems could only be explained by the participation of Ti(III) hydrides.

The dependence of the electrical conductivity of the polymethylalumoxane—pyridine system on the component ratio was studied. The structure and energy effects of the formation of complexes (including charged ones), which arise in interactions between pyridine, reactive fragments of polymethylalumoxane, and the natural concomitants of the latter (the most probable impurities that remain after the synthesis), namely, trimethylaluminum, H2O, and “simple” alumoxane, [Me2Al(μ-OAlMe2)]2, were calculated by the DFT method. It was found that, in the presence of traces of oxygen-containing donors (alumoxane and/or H2O), the concentration of ions in solution increased by many orders of magnitude and attained the value observed experimentally. The interaction of pyridine with polymethylalumoxane fragments caused the almost complete replacement of trimethylaluminum, which formed >Al*(Me)(μ-Me)2AlMe2 bridges with three-coordinate Al atoms in polymethylalumoxane (Al*), by pyridine. It was shown that an analysis of the dependence of the conductivity of polymethylalumoxane solutions containing “free” trimethylaluminum on the content of pyridine added allowed the concentrations of trimethylaluminum, both free and bound with polymethylalumoxane, to be determined.

Model reactions of the (≡Si-O-)3MIVH (1), (≡Si-O-)2MIVH2 (2), and (≡Si-O-)2MIIIH (3) hydrides, where M = Ti and Zr, immobilized on the surface of silica with methane and propane were studied by the density functional theory with the PBE functional. The reactions involved the breaking of C-H alkane bonds and the formation of the (≡Si-O-)3MR, (≡Si-O-)2M(H)R, and (≡Si-O-)2MR products (R = Me, n-Pr, and i-Pr), respectively. Reactions with the participation of 1 and 2 were found to occur as bimolecular processes without the formation of agostic-type prereaction complexes. With 3, the reaction was accompanied by the formation of stable prereaction and postreaction complexes. The conclusion was drawn that dihydrides 2 and trivalent metal hydrides 3 were much more reactive with respect to alkane C-H bonds than monohydrides 1. All the systems studied were characterized by low reaction regioselectivities.

The thermodynamic parameters of formation of ions in the system AlMe3 + electron donor (D) in the presence and absence of water microimpurities were determined. The structure of these ions was studied and their concentration in nonpolar media was estimated for the example of D = pyridine. The conclusion was drawn from the results of calculations that the participation of water resulted in a substantial increase in the concentration of ions.

The DFT method is used to study the interaction between metallocene catalyst precursors used in ethylene and propylene polymerization and two molecules of the Al-containing cocatalyst Al(C6F5)3. The participation of two Al centers in metallocene activation accounts for the catalytic activity and other properties of the catalytic systems. Two energy parameters characterizing the number of active sites and the polymerization rate per site are calculated.

Model reactions of silica-supported zirconium hydrides (≡Si—O—)3ZrH and (≡Si—O—)2ZrH2 with methane, resulting in cleavage of a C—H bond in the methane molecule and the formation of (≡Si—O—)3ZrCH3 and (≡Si—O—)2Zr(H)CH3 as products were studied using the DFT approach with the PBE density functional. The processes proceed as bimolecular reactions without preliminary formation of agostic complexes. According to calculations, zirconium dihydrides (≡Si—O—)2ZrH2 are more reactive toward the methane C—H bonds than zirconium monohydrides (≡Si—O—)3ZrH. The calculated activation energies of the reactions with participation of zirconium dihydrides (≡Si—O—)2ZrH2 are in better agreement with the known experimental data for the Yermakov—Basset catalytic system.

A DFT study of a model reaction [(η5-C5H5)2MCH3]+ + RH ⇌ [(η5-C5H5)2MR]+ + CH4 (M = TiIV, ZrIV; R = Me, Et, Pr, Pri) was carried out with the PBE density functional. Exchange of σ-bonded ligand proceeds through the formation of agostic complexes [Cp2M(RH)CH3]+ followed by their isomerization into complexes [Cp2M(CH4)R]+via an inner-sphere migration of a hydrogen atom. The calculated rate constants for such migrations involving the primary and secondary C--H bonds of propane molecule differ by 930 times for TiIV complexes and by 47 times for ZrIV complexes, which is due to the effect of steric factors.

Polymerization of ethylene on zirconocene catalysts was studied with the density functional theory. The approach proposed previously for the model system Cp2ZrEt++C2H4 was extended to substituted zirconocene catalysts (RCp)2ZrEt+, which allowed us to compare the results of calculations with the experimentally found rate constants of chain propagation. The ethyl fragment was demonstrated to be an adequate model for a growing polymer chain. The order of decrease in the activation energy of chain propagation calculated for compounds with R=H, Me, Prn, and Bun is in qualitative agreement with the experimental data. However, the quantitative description gave underestimated theoretical rate constants of chain propagation compared to the experimental values. In the case of polyalkyl-substituted zirconocenes (R=1.2-Me2 or Me4), no correlation between the calculated and experimental characteristics was observed. The results were explained using the simplest model reaction of the replacement of the MeMAO− counterion by an ethylene molecule accompanied by displacement of the former to the outer coordination sphere of the Zr atom. This step was demonstrated to control the kinetics of the process. It was concluded that the isolated-cation model used in early investigations is not adequate and calls for modification with regard to the effect of the counterion.

A DFT study of ethylene polymerization by zirconocene catalysts was carried out. Stationary points corresponding to intermediates and transition states were located on the potential energy surface of the [Cp2ZrC2H5]++C2H4 model system. Three possible reaction mechanisms involving the formation of β-agostic complexes were considered. The energy and thermodynamic characteristics for different reaction pathways were calculated. Corresponding activation energies lie in the range 3.9–6.8 kcal mol−1.

Reactions of methane and hydrogen molecules with [(η5-C5H5)2ZrCH3]+ and (η5-C5H5)2ZrH3]+ cations were studied using nonempirical density functional theory (DFT). In all cases, the reactions begin with the formation of agostic complexes between the substrate molecules and1 or2. Transformation of these intermediates into transition states when moving along the reaction coordinate requires only slight changes in the geometry. The dihydrogen molecule reacts with1 exothermically (−8.8 kcal mol−1) and barrierlessly to form2 and CH4. Exchange of σ-bonded ligands in the1−CH4 system proceeds through a symmetric transition state with an activation energy of 15.0 kcal mol−1. According to calculations, organometallic ZrIV complexes are promising for activation of C−H and H−H bonds under mild conditions.

Cyclopropyl type radicals\(X - _\triangledown \cdot (X = \begin{array}{*{20}c} \backslash \\ --- \\ / \\ \end{array} C, \begin{array}{*{20}c} \backslash \\ --- \\ / \\ \end{array} Si, \begin{array}{*{20}c} \backslash \\ --- \\ / \\ \end{array} Si---O)\) were identified on a surface of activated silica by ESR. The possibility of their preparation by two methods,i.e., by photocyclization of substituted allyl radicals and by interaction of cyclopropane molecules with particular surface defects, was demonstrated. The effects of β-substituents on radiospectroscopic characteristics and thermal stabilities of the radicals were studied. Rate constants and activation energies of decomposition of substituted cyclopropyl radicals were estimated. The experimental data obtained were compared with the results of quantum-chemical calculations of model systems. The mechanism of photocyclization of allyl radicals was discussed. The transition states of decomposition of cyclopropyl and β-fluorine-substituted cyclopropyl radicals were calculated. Electronegative substitution was found to result in a considerable decrease in the activation energy of the cyclopropane ring opening.

The reaction of β-substituted cyclopropyl radicals with CO was studied by ESR. Tile acyl radical resulting from the addition of CO to the cyclopropyl radical was detected. At temperatures near 270 K, an intramolecular rearrangement of the acyl radical affords substituted 2-oxocyclobutyl radicals (ring expansion reaction). Mechanisms for the free-radical transformations studied were suggested.

The reactions of methane and dihydrogen molecules with the cations [(η 5 -C 5 H 5 ) 2 MCH 3 ] + ( 1 ) and [(η 5 -C 5 H 5 ) 2 MH] + ( 3 ) (M=Zr, Ti) have been investigated by gradient-corrected density functional calculations. In the case of CH 4 , the active cationic center of 1 or 3 attracts the substrate molecule first to form an agostic complex in which its CH bond is already somewhat weakened. The σ-bonded ligand exchange reaction in the system 1 +CH 4 proceeds through a symmetric transition state with an activation barrier of 15.0 kcal mol −1 (11.6 kcal mol −1 ) for the Zr (Ti) complex. Hydrogen reacts with 1 exothermally, Δ H 0 =−7.1 kcal mol −1 (−8.6 kcal mol −1 ) for Zr (Ti), yielding 3 and CH 4 without an activation barrier. These theoretical results give insight into the mechanism of H/D exchange in methane in the presence of Ziegler–Natta-type catalysts observed experimentally by Grigoryan et al. It is shown that organometallic cationic complexes of Zr(IV) and Ti(IV) may prove to be promising systems for CH and HH bond activation under mild conditions.