A comparison of ring-chain tautomerism in heterocycles derived from 2-aminobenzenesulfonamide and anthranilamide

A number of anthranilamide and 2-aminobenzenesulfonamide derivatives with aromatic aldehydes and 1,3-dicarbonyl compounds were synthesized. Substituted benzaldehyde derivatives of neither aminoamides showed tautomerism in solutions. Reaction products of 2-aminobenzenesulfonamide with p-substituted benzoylacetic aldehydes and p-substituted benzoylacetones undergo ring-chain tautomerism with a good linear correlation between the ring-chain equilibrium constants (log K, where K=[ring]/[chain]) and the Hammett-Brown σ⁺ parameters of the aromatic substituents. The equilibrium constant was measured for the reaction products of 2-aminobenzenesulfonamide with unsubstituted benzoylacetaldehyde at several temperatures which enabled the enthalpy and entropy of this reaction to be evaluated.     

Theoretical study of the UV photodissociation of Cl2: potentials, transition moments, extinction coefficients, and Cl*/Cl branching ratio

Potential energy curves for the X (1)Sigma(g) (+) ground state and Omega=0(u) (+), 1(u) valence states and dipole moments for the 0(u) (+), 1(u)-X transitions are obtained in an ab initio configuration interaction study of Cl(2) including spin-orbit coupling. In contrast to common assumptions, it is found that the B (3)Pi(0(+)u)-X transition moment strongly depends on internuclear distance, which has an important influence on the Cl(2) photodissociation. Computed energy curves and transition moments are employed to calculate the A, B, C<--X extinction coefficients, the total spectrum for the first absorption band, and the Cl(*)((2)P(1/2))/Cl((2)P(3/2)) branching ratio as a function of excitation wavelength. The calculated data are shown to be in good agreement with available experimental results.     

On the ultraviolet photodissociation of H(2)Te

The photodissociation of H(2)Te through excitation in the first absorption band is investigated by means of multireference spin-orbit configuration interaction (CI) calculations. Bending potentials for low-lying electronic states of H(2)Te are obtained in C(2v) symmetry for Te-H distances fixed at the ground state equilibrium value of 3.14a(0), as well as for the minimum energy path constrained to R(1)=R(2). Asymmetric cuts of potential energy surfaces for excited states (at R(1)=3.14a(0) and theta;=90.3 degrees ) are obtained for the first time. It is shown that vibrational structure in the 380-400 nm region of the long wavelength absorption tail is due to transitions to 3A('), which has a shallow minimum at large HTe-H separations. Transitions to this state are polarized in the molecular plane, and this state converges to the excited TeH((2)Pi(1/2))+H((2)S) limit. These theoretical data are in accord with the selectivity toward TeH((2)Pi(1/2)) relative to TeH((2)Pi(3/2)) that has been found experimentally for 355 nm H(2)Te photodissociation. The calculated 3A(')<--XA(') transition dipole moment increases rapidly with HTe-H distance; this explains the observation of 3A(') vibrational structure for low vibrational levels, despite unfavorable Franck-Condon factors. According to the calculated vertical energies and transition moment data, the maximum in the first absorption band at approximately 245 nm is caused by excitation to 4A("), which has predominantly 2(1)A(") ((1)B(1) in C(2v) symmetry) character.     

Thermogravimetry of the NiO-Al2O3 system in a hydrogen flow

Thermogravimetry in a hydrogen flow is used to distinguish different forms of NiO-Al₂O₃ bonding at the temperatures of reduction of NiO. The influences of the temperature of preliminary treatment and the component ratio on the shapes of the TG and DTG curves of reduction were represented. By comparison of the results obtained with different weights and with different particle sizes, the influences of diffusion of water vapour in macropores on the characters of TG and DTG curves were studied. Different types of TG and DTG curves of reduction were observed:

1. Curves usual in thermal analysis, whose positions depend on the specimen weight and on the dispersity of the sample.
2. Curves whose position displays almost no change with variations of 1–2 orders the specimen weight.
3. Curves the number of reduction rate peaks in which depend on the experimental conditions.

     

GRECP/MRD‐CI calculations on the Hg atom and HgH molecule

Multireference single‐ and double‐excitation configuration interaction (MRD‐CI) calculations of transition energies for the Hg atom and spectroscopic constants for the HgH molecule are carried out with the generalized relativistic effective core potential (GRECP) method. A new selection criterium for the reference configurations is discussed. The calculated spectroscopic constants are compared with experimental data and results of calculations of other groups. Improvement of accuracy is mainly observed for bond lengths from the GRECP/MRD‐CI calculations (without applying the T = 0 correction) with respect to the results of other groups. Analysis of the quality of the approximations employed is carried out. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

GRECP/5e‐MRD‐CI calculation of the electronic structure of PbH

The correlation calculation of the electronic structure of PbH is carried out with the generalized relativistic effective core potential (GRECP) and multireference single‐ and double‐excitation configuration interaction (MRD‐CI) methods. The 22‐electron GRECP for Pb is used and the outer core 5s, 5p, and 5d pseudospinors are frozen using the level‐shift technique, so only five external electrons of PbH are correlated. A new configuration selection scheme with respect to the relativistic multireference states is employed in the framework of the MRD‐CI method. The [6, 4, 3, 2] correlation spin–orbit basis set is optimized in the coupled cluster calculations on the Pb atom using a recently proposed procedure, in which functions in the spin–orbital basis set are generated from calculations of different ionic states of the Pb atom and those functions are considered optimal that provide the stationary point for some energy functional. Spectroscopic constants for the two lowest‐lying electronic states of PbH (²Π_1/2, ²Π_3/2) are found to be in good agreement with the experimental data. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Arc discharge with a vaporizable anode: Why is the fullerene formation process affected by the kind of buffer gas?

A model for calculating an arc discharge with the vaporizable graphite anode used in production of fullerenes has been proposed. Calculations with the use of this model give a clue to the dependence of fullerene formation efficiency on the kind of buffer gas used.     

Ab initio calculations of the electronic states of AsH2 including dissociation characteristics

Multireference configuration interaction calculations have been carried out for low-lying electronic states of AsH(2). Bending potentials for the ten lowest states of AsH(2) are obtained in C(2v) symmetry for As-H distances fixed at the the ground state equilibrium value of 2.845 a(0), as well as for the minimum energy path constrained to R(1) = R(2). The calculated equilibrium geometries for the X?(2)B(1) ground state and the A?(2)A(1) excited state agree very well with the previous experimental and theoretical results, whereas the data for the higher-lying states are obtained for the first time. Asymmetric potential energy surface (PES) cuts (at R(1) = 2.845 a(0), θ = 90.7°) and two-dimensional (2D) PESs for the lowest three states are also new. The calculated ab initio data are used for analysis of possible AsH(2) photodissociation channels and predissociation effects. It is shown that the A?(2)A(1)-X?(2)B(1) transition dipole moment decreases with increasing bending angle, which influences the intensity distribution in the A?(0,0,0)→X? emission spectrum (v(2)' bending series), shifting its maximum to smaller v(2)' quantum numbers.     

Stereoselective reduction of the active substance of the medicinal preparation dimeb n to the corresponding cis- and trans-1,2,3,4,4a,9b-hexahydro derivatives

Convenient preparative methods have been developed for the reduction of the active substance of the medicinal preparation Dimebon (2,8-dimethyl-5-[2-(6-methylpyrid-3-yl)ethyl]-1,2,3,4-tetrahydro-γ-carboline) to the corresponding racemic cis- and trans-1,2,3,4,4a,9b-hexahydro derivatives, distinguished by a high degree of stereoselectivity. The structures of the obtained diastereomeric hexahydro-γ-carbolines were confirmed by various physicochemical methods, including X-ray structural analysis.