Band 55, Heft 8

It is argued that diffusion in biological and economical systems is better modelled by Cattaneo's equation where memory effects are included. Reaction diffusion equations using Cattaneo's system are derived for prisoner's dilemma (PD) and hawk-dove (HD) games. Nonlinear wave solutions are derived for them. As expected the asymptotic solution for the PD case is insufficient. Hence a cellular automata motivated by Cattaneo's system is used to show the existence of cooperation in the case of local game.

For the pyrochemical reprocessing of spent metallic nuclear fuels in molten salt baths it is important to investigate the behavior of the electrochemically negative elements Eu and Sr, which are significant fission products. Voltammetric and chronopotentiometric studies have shown that the reduction of Eu 2+ and Sr 2+ on liquid Pb cathodes in molten chloride baths at 1073 K follows the alloy formation reaction: Eu 2+ + 2e − + 3Pb → EuPb 3 and Sr 2+ + 2e − + 3Pb → SrPb 3 . In the present work these alloy formation reactions were studiedby electrochemical impedance spectroscopy. Analysis of the spectra showed that the electronic exchange of Eu 2+ /Eu and Sr 2+ /Sr is quasi-re-versible. Moreover, the experimental results allowed the determination of the kinetic parameters of EU 2+ /EU and Sr 2+ /Sr, the diffusion coefficients of these species in molten chloride baths, and also the diffusion layer thickness.

Dynamic Nuclear Polarization (DNP) studies of TANOL/water-glycerol solutions were per-formed at 1.53 mT. The samples have either various water-glycerol ratios at constant concentration or various concentrations at a constant water-glycerol ratio. The low field EPR spectra were recorded, the DNP parameters(enhancement factors, coupling constant, leakage factor) were determined, electronic relaxation times were measured. Depending on the values obtained, the interactions between nuclei and electrons are discussed.

The proton affinities of some primary, secondary, and tertiary amines have been calculated with different semiempirical and nonempirical quantum chemical methods. We were particularly interested in the question which of the most popular semiempirical methods yield good overall correlations between calculated and experimental values and, therefore, allow a reliable prediction of hitherto unknown proton affinities. We found that some of the most frequently used semiempirical methods result in good correlations only within the groups of primary, secondary and tertiary amines, while the overall correlation is even worse than the one obtained with the noniterative EHT method. Among the more recent methods which allow geometry optimizations (MINDO/3, MNDO, AMI, PM3, MSINDO) the best results have been calculated with the MSINDO method. Testing for the influence of geometry optimization we surprisingly found that two of these methods (MINDO/3, AMI) perform even better when geometry optimizations are omitted and standard bonding parameters are used instead. Superior results, however, have been obtained with the CNDO/2- and the INDO method. Finally, the best correlations between semiempirically calculated and experimental proton affinities have been achieved with the spectroscopic parametrizations of these methods, CNDO/2S and INDO/2S, respectively. The correlations resulting in these cases are close to those reached at the ZPE+MP2/6-31 l++G**//HF/6-311++G** level of ab initio theory and with a comparable DFT method. A preliminary investigation revealed that an improvement in the semiempirical calculation of proton affinities might be obtained if different U μμ parameters are used for the nitrogen atoms of primary, secondary, and tertiary amines.

A molecular beam Fourier transform microwave spectrometer, designed for the study of chemical reactions within electrical discharges, is described in detail. Applications include the production of carbonyl fluoride, ketene, acetic acid, and difluorocarbene. For the production of carbonyl fluoride and ketene with 1,1-difluoroethylene and carbon dioxide as precursor molecules a reaction path via a 2+2 cycloaddition is proposed.

The proton NMR spectra and spin-lattice relaxation times of tetrapentylammonium iodide have been measured between 100 K and the melting point. The room temperature crystal structure has been determined by X-ray diffraction as orthorhombic, space group Ccca, Z = 4 with a = 10.811(2), b = 22.771(5) and c = 9.500(2) Å with fully ordered tetrapentylammonium cations. The existence of a solid-solid phase transition at 400 K has been confirmed by DTA. The onset of C 3 methyl group reorientations characterized by Arrhenius activation parameters has been evidenced. The intracation conformational motions in the pentyl chains start to manifest themselves already at lower temperatures. The appearence of an ionic plastic phase with coexisting liquid-like and solid-like cations has been discovered.

The crystal structures of N-(substitutedphenyl)-2,2,2-trichloroacetamides of the type 2/3/4- XC 6 H 4 .NHCO.CCl 3 (X = CI, NO 2 or CH 3 ), namely, N-(3-nitrophenyl)-2,2,2-trichloroacetamide, 3-NO 2 C 6 H 4 .NHCO.CCl 3 (m-NO 2 PhTCA); N-(4-nitrophenyl)-2,2,2-trichloroacetamide, 4-NO 2 C 6 H 4 .NHCO.CCl 3 (p-NO 2 PhTCA); N-(2-chlorophenyl)-2,2,2-trichloroacetamide, 2-ClC 6 H 4 .NHCO.CCl 3 (o-ClPhTCA) and N-(4-chlorophenyl)-2,2,2-trichloroacetamide, 4- C1C 6 H 4 .NHCO.CCl 3 (p-ClPhTCA) have been determined at room temperature. The present data are analysed along with our earlier crystal structures of N-(2-nitrophenyl)-2,2,2-trichloroacetamide, 2-NO 2 C 6 H 4 .NHCO.CCl 3 (o-NO 2 PhTCA); N-(4-methylphenyl)-2,2,2-trichloroacetamide, 4-CH 3 C 6 H 4 . NHCO.CCl 3 (p-CH 3 PhTCA); N-(phenyl)-2,2,2-trichloroacetamide, C 6 H 5 .NHCO.CCl 3 (PhTCA); N-chloro-N-(phenyl)-2,2,2-trichloroacetamide, C 6 H 5 .NClCO.CCl 3 (NClPhTCA); and finally with N-(phenyl) acetamide, C 6 H 5 .NHCO.CH 3 (PhA). The crystal type, space group, formula units and lattice constants in Å of the new structures are; m-NO 2 PhTCA: triclinic, PI, Z = 4, a = 7.493(3), b = 9.992(3), c = 15.225(5), α = 84.16(2)°, β = 82.59(2)°, γ = 84.92(2); p-N02PhTCA: monoclinic, P2 1 /n, Z = 4, a = 5.807(2), b = 15.354(6), c = 12.475(5), β = 92.28(2)°; o-ClPhTCA: orthorhombic, Pna2 1 , Z = 4, a = 8.769(2), b = 12.838(3), c = 9.578(2) and p-ClPhTCA: orthorhombic, Pbca, Z = 8, a = 9.742(4), b = 10.031(4), c = 23.110(9). The compounds, m-NO 2 PhTCA, o-NO 2 PhTCA and p-CH 3 PhTCA show two molecules each in their asymmetric units. This is in agreement with the multiple lines observed in the 35 Cl NQR spectra of the latter two compounds. But the presence of two molecules in the asymmetric unit of m- NO 2 PhTCA indicates that it may undergoe a phase transition below room temperature. The bond lengths and bond angles are normal except for some deviations. The presence of strong electron withdrawing group at the ortho position of the phenyl ring and N-chlorination of the amide will have significant effect on some bond distances and bond angles.

To study the effect of electron donating or repelling group substitution in the phenyl ring on the γ( 35 Cl NQR of Cl(ω)) of the dichloroacetyl group, several N-(methylsubstituted-phenyl)-2,2-dichloroacetamides have been synthesised, characterised and their 35 Cl NQR frequencies mea-sured at 77 K. All the substituted amides, except N-(2,5-dimethylphenyl)-2,2-dichloro-acetamide, show two ω-C-Cl frequencies in the range of 37.009 -38.014 MHz. N-(2,5-dimethylphenyl)-2,2-dichloroacetamide shows one u-C-C 1 NQR frequency at 37.50 MHz for the two chlorine atoms present. The two atoms may be crystallographically equivalent. The frequencies of all the methyl-substituted dichloroacetamides have been compared and correlated alongwith the corresponding chloro substituted-phenyl dichloroacetamides. The γ( 35 C1 NQR) of Cl(ω) of all the N-(substituted-phenyl)-2,2-dichloroacetamides have been correlated with the NQR substituent parameters (κ i ), assuming additivity of the substituent effects. The frequencies are also correlated with Hammett a. The effect of ring substitution on the average 35 Cl NQR Cl(ω) frequencies of the dichloroacetyl group is not substantial, but it affects the crystal structures of the substituted compounds. Using the K i values for various groups and ω-C-Cl NQR frequencies of N-(phenyl)-2,2-dichloroacetamide (37.195 and 37.596 MHz), 7(35 C1 NQR) of all the N-(methyl and chlorosubstitutedphenyl)-2,2-dichloroacetamides have been estimated. Similar calculations are extended to all the N-(methyl and chlorosubstitutedphenyl)-2-chloroacetamides and -2,2,2-trichloroacetamides. There is a rea-sonably good agreement between the computed and the experimental values for all the three groups of compounds. Further, γ( 35 Cl NQR of Cl(ω) of all the substituted N-phenyl-chloroacetamides represented by the general formula X y C 6 H 5- y NHCOR (where X = Cl, or CH 3 , y = 1 or 2 and R = CH 2 Cl, CHCl 2 or CCl 3 ) are compared. The γ( 35 Cl NQR of Cl(ω)) of the substituted N-(phenyl)-2,2-dichloroacetamides lie between the frequencies of the corresponding substituted N-(phenyl)-2-chloroacetamides and substituted N-(phenyl)-2,2,2-trichloroacetamides.

The Electron Paramagnetic Resonance spectra of Cu 2+ in CdCa (CH 3 COO)4 • 6H 2 O (cadmium calcium tetraacetate hexahydrate) powder and single crystal have been recorded at 300 and 133 K. The angular variation of the spectra indicated the substitution of the host Cd 2+ with Cu 2+ . The observed values of the g and A hyperfine tensors were found to be temperature dependent, and this dependence is discussed and explained on the basis of dynamic Jahn-Teller effects. The spin-Hamiltonian parameters were found to be axial symmetric at room temperature, whereas they showed deviations from axial symmetry at low temperature. The g and A tensors where found to be coaxial within the limits of experimental errors, and the ground state wave functions of the complex at 300 and 133 K have been constructed.

Three liquid crystalline (LC) substances with the cyano-groups attached at the lateral positions to the molecular cores were studied with the aid of dielectric spectroscopy methods. The high frequency relaxation process connected with the molecular reorientations around the long molecular axes was studied in the isotropic, nematic and several smectic phases. The dielectric spectra are rather complex, indicating a contribution from several molecular processes to the main relaxation process. The dielectric time changes smoothly at the phase transitions between "liquid-like" phases (isotropic -nematic -smectic A -smectic C), and becomes shorter at the transition to the "solid-like" smectic G phase with a low-ering of the activation barrier. This indicates that the molecules perform broad angle librational motions rather than overall rotational motions in this phase. In case of a substance having two cyano groups at-tached to the benzene ring, a pronounced jump-wise change of the relaxation time was observed at the isotropic -smectic A transition.

The photophysical characteristics of a group of coumarins with a 3:4-fused ring system (2-substitut-ed-4,5-dioxo-l,2-dihydro-4H,5H-pyrano-[3:4-c] [1]-benzopyrans) in solutions at room temperature, in frozen ethanol matrix at 77 K, in solid phase and in PVC films are reported. The low fluorescence quan-tum yield of the compounds investigated in solution is explained as a result of internal conversion from the fluorescent S 2 (ππ*) state to the lower lying S 1 (nπ*) state. The phosphorescence with a life time in the order of seconds is connected with intersystem crossing S 1 (nπ*) -T 1 (ππ*). The absorption Franck Condon transitions in solid phase and in PVC matrix are only weekly batochromically shifted accord-ing to solution.