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51.
The additions of various five-membered ring aminoheterocycles to α-cyanocinnamonitriles were studied. Regiochemistry of product formation can in most cases be controlled by choosing the appropriate electrophile. An α-cyanocinnamonitrile with an additional β-leaving group normally provides products arising from initial attack of the ring amino group, while exo attack predominates in the case of the parent α-cyanocinnamonitrile. Aminopyrazole and aminoindazole provide only exo products with either electrophile. Product assignments were made via X-ray and 2D NMR methods; these assignments serve as a benchmark to several literature references and to future investigations of conjugate additions of these nucleophiles. 相似文献
52.
Intermolecular potentials have been obtained from high-energy total cross sections for several alkali metal systems: CS + He, Ne, Ar, CH3NO2; K + CH4, C(CH3)4, C6H6, c-C6H12, CH3I, CCl4, SF6, N2. For the CS-rare gas cases and K + N2 only the repulsive part was determined. For the rest both attractive and repulsive parts were seen. 相似文献
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J. D. Cross I. M. Dale A. C. D. Leslie H. Smith 《Journal of Radioanalytical and Nuclear Chemistry》1979,48(1-2):197-208
The normal levels of arsenic in human tissue are reported together with the arsenic concentrations found in the investigation
of a large number of industrial exposure incidents. These results are useful for establishing that industrial exposure has
taken place and for confirming arsenic poisoning but they cannot be used realistically to predict that any person or group
will suffer a visible deterioration in health because no correlation between arsenic contamination and symptoms can be made.
Industrial workers who are affected by arsenic exposure are often no more exposed than their co-workers. 相似文献
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The electron transmission efficiency as a function of kinetic energy for an electron spectrometer operating in the fixed analyser transmission (FAT) mode has been determined by direct comparison with the known transmission efficiency in the fixed retard ratio (FRR) mode. Results obtained from the background intensity and from the relative peak heights of a number of elements compare well with each other. They suggest that transmission in the FAT mode is nearly independent of kinetic energy. 相似文献
60.
A comparative study of seven discretization schemes for the equations describing convection-diffusion transport phenomena is presented. The (differencing) schemes considered are the conventional central- and upwind-difference schemes, together with the Leonard,1 Leonard upwind1 and Leonard super upwind difference1 schemes. Also tested are the so called locally exact difference scheme2 and the quadratic-upstream difference scheme.3,4 In multidimensional problems errors arise from ‘false-diffusion’ and function approximations. It is asserted that false diffusion is essentially a multidimensional source of error. No mesh constraints are associated with errors in function approximation and discretization. Hence errors associated with discretization only may be investigated via one-dimensional problems. Thus, although the above schemes have been tested for one- and two-dimensional flows with sources, only the former are presented here. For 1D flows, the Leonard super upwind difference scheme and the locally exact scheme are shown to be far superior in accuracy to the others at all Peclet numbers and for most source distributions, for the test cases considered. Furthermore, the latter is shown to be considerably cheaper in computational terms than the former. The stability of the schemes and their CPU time requirements are also discussed. 相似文献