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The azido tetrazolo valence isomerism of twenty 9-methyl-s-triazolo[4,3-c]tetrazolo[1,5-a]pyrimidines with different substituents at position 5 has been studied by means of 1H NMR spectroscopy. All the compounds have been found to be tetrazoles in the solid state and in (CD3)2SO solution; in CF3COOH azido and tetrazolo isomers are in equilibrium. From equilibrium constants K and thermodynamic data determined it is concluded that in this series K depends on both electronic effects and steric requirements of the 5-substituents. A linear relation between K and σ was found for 5-arylderivatives because ΔS° keeps approximately constant and the substituent mainly operates on ΔH°. 相似文献
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Covalent and noncovalent chemistries that are selective to single-walled carbon nanotubes of a particular electronic type have become increasingly important for electronic structure separation and on-chip modification of nanoelectronic devices. By monitoring transient Raman spectroscopy and photoluminescence (PL) during a reaction with 4-chlorobenzene diazonium in aqueous solution, evidence for a characteristic two-step mechanism with two distinct time constants is uncovered. A long-lived intermediate selectively and noncovalently binds and partially dopes the nanotube surface (tau = 2.4 min). A slower, covalent reaction is tracked using the time-dependent increase in the disorder mode in Raman (tau = 73 min). The transient Raman and PL data are well described using a series of two first-order reactions. The covalent bonding step can be deactivated by changing the structure of the surfactant adsorbed phase, further supporting the mechanism. 相似文献
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Ohne Zusammenfassung 相似文献
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G. Patein Esbach Denigès E. W. T. Jones E. O. von Lippmann und F. Soxhlet 《Fresenius' Journal of Analytical Chemistry》1907,46(5):339-341
Ohne Zusammenfassung 相似文献
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Summary The mean rise in temperature with plastic strain due to the work of plastic deformation, taking account of the temperature-dependence
of yield stress, is investigated when conduction effects are neglected and results for one particular example are presented.
An adaptation of the well-known Siebel-Karman analysis for sheet rolling is examined, and results for the particular case
of rolling a medium carbon steel are given in detail. The temperature-dependent property of the yield stress in cold-rolling
at moderate reductions is shown not to have a large effect on factors such as roll-torque, though the actual temperature increase
generated is a significant one. Examples are given of how the temperature of the material increases in its passage through
the roll gap. 相似文献