Kinetic parameters of decomposition of some selenites

Studying the kinetics of isothermal decomposition of thirteen selenites at isothermal heating, the values of activation energy E of the process, pre-exponential factor A in Arrhenius equation and changes of entropy for the formation of the activated complex of the reagent were calculated. Direct dependence between the thermal stability of the selenites and their cation radii on their 'hardness' or 'softness' was found. The dependence was interpreted in the terms of the generalized perturbation theory of chemical reactivity. Kinetic compensation effect was observed only for the selenites, which thermally decompose by the same mechanism.     

Study on the Kinetics of Non-isothermal Dehydration of Alkaline Earth Metal Selenites

Summary. The dehydration kinetics of crystallohydrates of beryllium, magnesium and calcium selenites were studied under non-isothermal conditions. The values of the activation energy of dehydration, the pre-exponential factor in Arrhenius equation and the change of entropy for the formation of the activated complex were calculated using the calculation procedure of Coats and Redfern. Thermal stability and activation energy of dehydration of the crystallohydrates were found to increase by the same order. The relationships observed were interpreted using Klopman’s generalized perturbation theory of chemical reactivity. The same theory was applied to explain the differences in the IR spectra of the selenite crystallohydrates studied.     

Application of the many-body perturbation theory to normal saturated hydrocarbons in the localized representation

The second-order energy corrections are calculated for some normal saturated hydrocarbons by using the many body-perturbation theory (MBPT) based on localized orbitals. The correlation energies are expressed as the sum of contributions from virtual orbital pairs. We have found that these contributions are transferable and have interesting structural features: the trans-coplanar effects are relatively large. Partitioning the correlation energies according to the order of neighbourhood we have found that the zero order effects are the largest but the first and second neighbour contributions are also important.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday     

Use of Thermal Analysis in the Study of Sodium Carbonate Causticization by Means of Dolomitic Lime

Dolomitic lime samples were treated with sodium carbonate solution and the causticizing process was followed at different temperatures by recording the TG and DTA curves of the solid-phase products that separated after different time intervals. The chemical reactions occurring during causticization are discussed. From the TG curves, apparent kinetic parameters were derived. Some aspects of the kinetic compensation effect are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Energy decomposition in the topological theory of atoms in molecules and in the linear combination of atomic orbitals formalism: a note

 It is shown that the molecular energy calculated at the self-consistent-field level can be strictly expressed as a sum of one- and two-atom energy components in the framework of Bader's topological theory of atoms in molecules (AIM). The expressions of our recent “chemical energy component analysis” can be obtained from the AIM ones as some linear combination of atomic orbitals mappings of the integrations over the atomic basins. Received: 15 June 2000 / Accepted: 4 October 2000 / Published online: 19 January 2001     

Salt effects in the mercuration of unsaturated compounds. Kinetic evidence for the formation of ion pairs and a solvated ion

The kinetics of mercuration of bornylene and cyclohexene in different solvents in the presence of NaOAc and LiClO₄ has been investigated. Addition of NaOAc sharply decreases the rate of addition reactions of mercuric acetate to bornylene and cyclohexene in alcohols; the main direction of the mercuration of bornylene is the formation of acetoxy-adducts, and the yield of solvo-adducts decreases from 76 % in the absence of NaOAc, to 19 % in the presence of the salt (4·10^–3 mol L^–1). A reaction scheme involving the participation of intermediate ion pairs and a solvated mercurinium ion is suggested and confirmed by a steady-state concentration method. The influence of NaOAc on the rate of the reaction and on product formation is realized through the common ion effect.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 819–826, May, 1994.     

The perturbation theory model of a spherical oscillator in electric field and the vibrational stark effect in polyatomic molecular species

The effect of external electrostatic fields on the spherical oscillator energy states was studied using stationary perturbation theory. Besides the spherical oscillator with ideal symmetry, also a variety of the deformed systems were considered in which the deformations may be induced by the external fields, but also by the short-range crystal lattice forces. The perturbation theory analysis was carried out using the field-dependent basis functions. Predicted spectral appearances and band splittings due to the deformations and external field influences were shown to be helpful in interpreting the experimental spectra of molecular oscillator possessing subsets of mutually orthogonal triply degenerate normal modes (such as, e.g. tetrahedral species). To verify the results of the perturbation theory treatments, as well as to provide a further illustration of the usefulness of the employed technique, a numerical HF/aug-cc-pVTZ study of the vibrational states of methane molecule in external electrostatic field was performed.     

Interaction of the atoms in molecules of pyridine and its derivatives according to the results of ab initio calculations

Nonempirical quantum-chemical calculations of pyridine and its 2-, 3-, and 4-X-substituted derivatives (X = F, Cl, Br, Me, and Et) by RHF/6-311G(d) and MP2/6-311G(d) methods indicate an alternation of charges on the atoms of the pyridine ring and of the occupancy of their valence p_y-orbitals. This is caused by the polarization of bonds under the action of the charges of the atoms geminal to C(n). Bonding molecular orbitals in these molecules, formed as a result of the p_y-orbitals, occurring in the plane of the pyridine ring, are not an indication (characteristic) of p, π-conjugation between the unshared electron pair of the heteroatom of a substituent X and the π-electron system of the ring. The results of the calculations by these methods did not differ in principle. Dedicated to Academician of the Russian Academy of Sciences M. G. Voronkov in honor of his 85^th birthday. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1671–1681, November, 2006.     

Basic theory and some applications concerning the ratio of shear viscosity to entropy density in dense fluids

Much interest continues relating to the conjecture from string theory of an inequality satisfied by the ratio η/s in dense fluids, where η is the shear viscosity and s the entropy density. First, we summarise the models which have prompted the proposal of the inequality. Second, we consider a model equation of state which may be appropriate for the dense fluids NH₃ and H₂O, both of which satisfy the inequality.     

Effects on the Reactivity by Changing the Electrophilic Center from CO to CS: Contrasting Reactivity of Hydroxide,p‐Chlorophenoxide,and Butan‐2,3‐dione Monoximate in DMSO/H2O Mixtures

Second‐order rate constants have been measured spectrophotometrically for the reactions of O‐p‐nitrophenyl thionobenzoate ( 1 , PNPTB) with HO^?, butan‐2,3‐dione monoximate (Ox^?, α‐nucleophile), and p‐chlorophenoxide (p‐ClPhO^?, normal nucleophile) in DMSO/H₂O of varying mixtures at (25.0±0.1) °C. Reactivity of these nucleophiles significantly increases with increasing DMSO content. HO^? is less reactive than p‐ClPhO^? toward 1 up to 70 mol % DMSO although HO^? is over six pK_a units more basic in these media. Ox^? is more reactive than p‐ClPhO^? in all media studied, indicating that the α‐effect is in effect. The magnitude of the α‐effect (i.e., k/k_p) increases with the DMSO content up to 50 mol % DMSO and decreases beyond that point. However, the dependency of the α‐effect profile on the solvent for reactions of 1 contrasts to that reported previously for the corresponding reactions of p‐nitrophenyl benzoate ( 2 , PNPB); reactions of 1 result in much smaller α‐effects than those of 2 . Breakdown of the α‐effect into ground‐state (GS) and transition‐state (TS) effects shows that the GS effect is not responsible for the α‐effect across the solvent mixtures. The role of the solvent has been discussed on the basis of the bell‐shaped α‐effect profiles found in the current study as well as in our previous studies, that is, a GS effect in the H₂O‐rich region through H‐bonding interactions and a TS effect in the DMSO‐rich media through mutual polarizability interactions.     

Effect of substituents on the catalytic properties of bis(cyclopentadienyl)zirconium dichloride complexes with polymethylaluminoxane and AlBu1 3/CPh3B(C6F5)4 cocatalysts in ethylene polymerization

The catalytic properties of the complexes (RCp)₂ZrCl₂ (R=H, Me, Prⁱ, Buⁿ, Buⁱ, Me₃Si,cyclo-C₆H₁₁), and Me₂SiCp^*NBuⁱZrCl₂ (Cp^*=C₅(CH₃)₄) combined with the AlBuⁱ ₃−CPh₃B(C₆F₅)₄ cocatalyst in ethylene polymerization were studied. The specific activity of the substituted bis-cyclopentadienyl complexes decreases in the sequence: Me>Prⁱ>Buⁿ>Buⁱ>Me₃Si>cyclo-C₆H₁₁, which corresponds to the activity sequence for these complexes activated by polymethylaluminoxane (MAO) but is 4–20 times lower in absolute value. Comparison of the polyethylene samples obtained in the presence of the same complexes with MAO and AlBuⁱ ₃−CPh₃B(C₆F₅)₄ cocatalysts showed that polyethylene with much higher molecular mass, melting point, and crystallinity is formed in the presence of the ternary catalytic systems, and this indicates a different nature of the active sites of the catalytic systems. The effective activation energy of polymerization (≈3.6 kcal mol⁻¹), first order with respect to monomer and ≈0.4 order with respect to organoaluminum component, was found for the (PrⁱCo)₂ZrCl₂−AlBuⁱ ₃−CPh₃B(C₆F₅)₄ catalytic system. It was proposed on the basis of the kinetic data that AlⁱBu₃ enters into the composition of the active site to form a bridged heteronuclear cationic complex. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp 301–307, February, 2000.