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491.
The substitution structure (rs) of ethyleneimine (aziridine) has been found by analysis of microwave gas spectra of the parent molecule and of the necessary number (5) of mono-isotopically substituted species, all of which were chemically enriched. Two coordinates (<0.1 Å) had to be derived using the conditions Σmici = Σmibici = 0. Data from microwave spectra of two double-isotopically substituted species [1-D]-, [1−15N]-ethyleneimine, and [2,2'-D2]-ethyleneimine were applied as a further check. The agreement was satisfactory. In the resulting rs structure the C-C distance is shorter than the C-N distance, in accordance with the larger nuclear charge of nitrogen compared to carbon, but qualitatively disagreeing with the results of earlier investigations. Also, the plane defined by H(2), C(2), H(2') is not perpendicular to the N(1), C(2), C(3) plane as assumed earlier. The former plane forms and angle of 87° with the latter which, however, almost exactly bisects the HCH angle. The CH2 groups may, therefore, be described as slightly “twisted”. 相似文献
492.
Reversible Guest Binding in a Non‐Porous FeII Coordination Polymer Host Toggles Spin Crossover 下载免费PDF全文
Dr. Anders Lennartson Dr. Peter Southon Dr. Natasha F. Sciortino Prof. Cameron J. Kepert Prof. Cathrine Frandsen Prof. Steen Mørup Dr. Stergios Piligkos Prof. Christine J. McKenzie 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(45):16066-16072
Formation of either a dimetallic compound or a 1 D coordination polymer of adiponitrile adducts of [Fe(bpte)]2+ (bpte=[1,2‐bis(pyridin‐2‐ylmethyl)thio]ethane) can be controlled by the choice of counteranion. The iron(II) atoms of the bis(adiponitrile)‐bridged dimeric complex [Fe2(bpte)2(μ2‐(NC(CH2)4CN)2](SbF6)4 ( 2 ) are low spin at room temperature, as are those in the polymeric adiponitrile‐linked acetone solvate polymer {[Fe(bpte)(μ2‐NC(CH2)4CN)](BPh4)2 ? Me2CO} ( 3? Me2CO). On heating 3? Me2CO to 80 °C, the acetone is abruptly removed with an accompanying purple to dull lavender colour change corresponding to a conversion to a high‐spin compound. Cooling reveals that the desolvate 3 shows hysteretic and abrupt spin crossover (SCO) S=0?S=2 behaviour centred at 205 K. Non‐porous 3 can reversibly absorb one equivalent of acetone per iron centre to regenerate the same crystalline phase of 3? Me2CO concurrently reinstating a low‐spin state. 相似文献
493.
Micellar systems composed of surfactants are used extensively in academia and industry for many different applications. In this work a highly versatile CE method for determination of CMCs of charged surfactants has been developed. In the case of positively charged surfactants a coating procedure of the fused-silica capillary was used, whereas negatively charged surfactants were analyzed using uncoated capillaries. The CE method is based on frontal analysis (FA) employing use of contactless conductivity and UV detection. The main advantages of the method are that it can be used for non-UV absorbing surfactants without introducing marker compounds which previously has been found to affect CMCs, requires very limited sample volume and is easily implemented and automated using standard CE equipment. The fact that counterions and different aggregated states are separated allows a detailed characterization of the micelle systems using the developed method. In the case of UV absorbing surfactants similar results were obtained employing contactless conductivity and UV detection. Finally, CMCs obtained using conductometry gave similar results as compared to the developed CE-FA procedure. 相似文献
494.
de Klerk W. P. C. Schrader M. A. van der Steen A. C. 《Journal of Thermal Analysis and Calorimetry》1999,56(3):1123-1131
Compatibility is an important safety aspect related to the production and storage of energetic materials. To test different
combinations of materials a simple test method with clear criteria is advisable. At the last ESTAC the use of microcalorimetry
and the vacuum stability test for the compatibility testing of propellants were presented. This paper presents DSC, DTA/TG
and (pressure) vacuum stability test results for the same combination. For three polymers (PMMA, PVC and CA) the results for
all tests are the same. Only Nylon-6/6 gives a variable result for the different test methods.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
495.
Jørgen Houmøller Sydney H. Kaufman Dr. Kristian Støchkel Prof. Lokesh C. Tribedi Prof. Steen Brøndsted Nielsen Prof. J. Mathias Weber 《Chemphyschem》2013,14(6):1133-1137
We report electronic spectra of mass‐selected MnO4? and MnO4??H2O using electronic photodissociation spectroscopy. Bare MnO4? fragments by formation of MnO3? and MnO2?, while the hydrated complex predominantly decays by loss of the water molecule. The band in the visible spectral region shows a well‐resolved vibrational progression consistent with the excitation of a Mn? O stretching mode. The presence of a single water molecule does not significantly perturb the spectrum of MnO4?. Comparison with the UV/Vis absorption spectrum of permanganate in aqueous solution shows that complete hydration causes a small blueshift, while theoretical models including a dielectric medium have predicted a redshift. The experimental data can be used as benchmarks for electronic structure theory methods, which usually predict electronic spectra in the absence of a chemical environment. 相似文献
496.
In this paper, we introduce the p-adic Moufang condition for hyperbolic buildings of rank 3. It is the most obvious and simplest generalization of the p-adic Moufang condition for affine buildings, introduced in Part III of this sequence of papers. We show that p is very restricted, which confirms (but does not prove) the conjecture that no p-adic analogue is possible for the construction of Moufang (hyperbolic) buildings by Ronan and Tits. 相似文献
497.
Koster S Duursma MC Boon JJ Heeren RM Ingemann S van Benthem RA de Koster CG 《Journal of the American Society for Mass Spectrometry》2003,14(4):332-341
Electron capture dissociation (ECD) of doubly protonated hyperbranched polyesteramide oligomers (1100-1900 Da) was examined and compared with the structural information obtained by low energy collisionally activated dissociation (CAD). Both the ester and amide bonds of the protonated species were cleaved easily upon ECD with the formation of odd electron (OE(.+)) or even electron (EE(+)) fragment ions. Several mechanistic schemes are proposed that describe the complex ECD fragmentation behavior of the multiply charged oligomers. In contrast to studies of biomolecules, the present results indicate that consecutive cleavages induced by intramolecular H-shifts are significant for ECD and of less importance for low energy CAD. The capture of an electron by the ionized species results in fragmentation associated with a redistribution of the excess internal energy over the products and the subsequent bond cleavage. Low energy, multiple collision CAD is found to be a more selective dissociation method than ECD in view of the observation that only amide bonds are cleaved for most of the hyperbranched polymers examined with CAD in this study. ECD appears not to provide complementary structural information compared to CAD in the study of hyperbranched polymers, even though a significantly more complex ECD fragmentation behavior is observed. ECD is shown to be of use for the structural characterization of large oligomers that may not dissociate upon low energy CAD. This is a direct result of the fact that ECD produces ionized hyperbranched oligomers with a relatively high internal energy. 相似文献
498.
Steen Ingemann Els Kluft Nico M. M. Nibbering Colin E. Allison Peter J. Derrick Steen Hammerum 《Journal of mass spectrometry : JMS》1991,26(10):875-881
The intramolecular secondary isotope effects on the α-cleavage of deuterium-labelled N-methyldipentylamine radical cations have been studied as a function of ion lifetime by field ionization kinetics. The isotope effects observed are all normal and increase in magnitude with increasing ion lifetime, with the exception of the δ-labelled compound which shows an inverse effect (predominant loss of the labelled radical) at times shorter than 10?9 s, and a normal effect at longer times. The isotope effects reflect differences in zero-point energies of the transition states as well as the influence of slight reductions of isotope-dependent frequencies on the state sums–a statistical weight effect. The latter is particularly important at high ion energies and is the primary reason for the occurrence of the inverse isotope effect. The time dependence of the normal and inverse isotope effect is reproduced by QET/RRKM calculations. 相似文献
499.
Spectral pairs in cartesian coordinates 总被引:1,自引:0,他引:1
Palle E. T. Jorgensen Steen Pedersen 《Journal of Fourier Analysis and Applications》1999,5(4):285-302
Let d have finite positive Lebesgue measure, and let
() be the corresponding Hilbert space of
-functions on . We shall consider the exponential functionse
on given bye
(x)=e
i2·x
. If these functions form an orthogonal basis for
(), when ranges over some subset in
d
, then we say that (, ) is a spectral pair, and that is a spectrum. We conjecture that (, ) is a spectral pair if and only if the translates of some set by the vectors of tile d. In the special case of =Id, the d-dimensional unit cube, we prove this conjecture, with =Id, for d3, describing all the tilings by Id, and for all d when is a discrete periodic set. In an appendix we generalize the notion of spectral pair to measures on a locally compact abelian group and its dual.Acknowledgements and Notes, Work supported by the National Science Foundation.Dedicated to the memory of Irving E. Segal 相似文献
500.
On the product of two generalized derivations 总被引:2,自引:0,他引:2
Mohamed Barraa Steen Pedersen 《Proceedings of the American Mathematical Society》1999,127(9):2679-2683
Two elements and in a ring determine a generalized derivation on by setting for any in . We characterize when the product is a generalized derivation in the cases when the ring is the algebra of all bounded operators on a Banach space , and when is a -algebra . We use these characterizations to compute the commutant of the range of .