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991.
Fluorescence lifetime measurements of rhodamine B in ethanol solution have confirmed the presence of two distinct species dependent on acidity. Rotational diffusion times of these species are identical and we propose that they are the acid and base forms of the dye. Species having identical spectra to these forms have also been obtained in concentration dependent studies and we believe that here, too, the equilibrium is acid—base rather than monomer—dimer as had been suggested.  相似文献   
992.
R.M. Dupeyre  A. Rassat 《Tetrahedron》1978,34(10):1501-1507
Complete determination of all proton hyperfine splitting constants in magnitude and sign, and their specific assignment in two stable rigid nitroxides are presented. Long range γ-splitting has been calculated by an MO method (INDO approximation) and by a modification of a valence bond calculation. The results are consistent with a non-planar and rapidly inverting NO group.  相似文献   
993.
-Fluorosulfatoperfluoroethyl isopropyl ketone I and fluorosulfatopentafluoroacetone II react with alkali metal chlorides and bromides to form the corresponding -haloperfluoro ketones as a result of direct nucleophilic substitution.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2066–2069, September, 1990.  相似文献   
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998.
The intersystem crossing decay constants from the 3B2u state into the ground state of anthracene-d10 in a phenazine crystal have been determined by magnetic resonance techniques at 1.5°K both at high magnetic field and, by a parameterization procedure, at zero magnetic field. A comparison of the anthracene-d10 zero-field results with those for anthracene-h10 show the effects of deuterium substitution to be largest for the in-plane spin levels of the anthracene triplet state.  相似文献   
999.
Summary When measuringQ –1 and the flexural resonance frequency of bars clamped at one end, constituted by a viscoelastic polymeric material glued to a rigid support of modulusE 1, it is possible to calculate the componentsE 2 andE 2 of the complex elastic modulus of the polymeric material examined. In this work the minimum (critical) value of the ratioa=E 2 /E 1=a c and the values of the ratioQ 2 –1/Q –1=F 1 are evaluated beyond which no exact calculation ofE 2 and ofQ 2 –1 is possible.Within the confidence limits of the linear viscoelasticity theory, these values depend on the accuracy of measurement of both frequency and resonance curve, as well as on the instrument employed, on the operating temperature and on the ratio between the thicknesses of the two coupled materials.In order to keep outside the critical conditions, the most convenient method involves the use of measurements of coupled test-pieces having different ratiosz between their thicknesses and of supports having different modulusE 1, depending on the field of temperature of the analysis ofE 2 and tg 2 concerning and E.P.R. elastomer and a vulcanized cis-1,4 polyisoprene in very wide ranges of temperature comprising the glass transition. Moreover, it is demonstrated by analysis the shift on the temperature axis of the tg maximum of the composite test-piece with respect to the position of the tg maximum of the polymeric material alone.With 11 figures and 1 table  相似文献   
1000.
The salts and quaternary derivatives of 2-methylene-3-hydroxyquinuclidine readily add nucleophilic reagents because of the high polarity and polarizability of the carbon-carbon double bond, which are due to the overall electron-acceptor effect of the positively charged nitrogen atom and the carbonyl group. The double bond is substantially deactivated in the base, and the addition of nucleophilic reagents is hindered.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1370–1376, October, 1977.  相似文献   
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