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151.
Akimoto Tachibana Masahiko Koizumi Iwao Okazaki Hiroyuki Teramae Tokio Yamabe 《Theoretical chemistry accounts》1987,71(1):7-19
The non- and fluorine-substituted singlet carbonyl ylides are studied by using ab initio MCSCF calculations. The thermodynamic stability of the carbonyl ylides and the intramolecular stability to isomerization or fragmentation reaction coordinates is demonstrated in terms of the topological structure of the ab initio potential energy surfaces. The allylic resonance is found to be dynamically unstable, considering out-of-plane vibrational mode. The instability is studied by the symmetries of the low-lying excitations out of the MCSCF wave function. 相似文献
152.
Kaishuo Yang Ehsan Sadeghi Pouya Libin Liu Dr. Ming Li Dr. Xiaoxian Yang Dr. Neil Robinson Prof. Eric F. May Prof. Michael L. Johns 《Chemphyschem》2022,23(4):e202100794
Understanding the behaviour of short-chain hydrocarbons confined to porous solids informs the targeted extraction of natural resources from geological features, and underpins rational developments in separation, storage and catalytic conversion processes. Herein, we report the application of low-field (12.7 MHz) 1H nuclear magnetic resonance (NMR) relaxation measurements to characterise ethane dynamics within mesoporous silica materials exhibiting mean pore diameters between 6 and 50 nm. Our measurements provide NMR-based adsorption isotherms within the range 25–50 bar and at ambient temperature, incorporating the ethane condensation point (40.7 bar at our experimental temperature of 23.6 °C). The quantitative nature of the acquired data is validated via a direct comparison of NMR-derived excess adsorption capacities with ex situ gravimetric ethane adsorption measurements, which are demonstrated to agree to within 0.2 mmol g−1 of the observed ethane capacity. NMR relaxation time distributions are further demonstrated as a means to decouple interparticle and mesopore dominated adsorption phenomena, with unexpectedly rapid relaxation rates associated with interparticle ethane gas confirmed via a direct comparison with NMR self-diffusion analysis. 相似文献
153.
The possibility of detection of the electron spin of a single paramagnetic species (an atom, a radical, or an ion) on the
surface was discussed. The analysis was based on spin chemistry laws taking into account the statistics of the spin states
of both the tunneling electron and paramagnetic center. The equations for the tunneling current as a function of temperature
and magnetic field strength were derived.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1732–1734, September, 1998. 相似文献
154.
Paramagnetic metal ions bound to proteins generate a dipolar field that can be accurately probed by pseudocontact shifts (PCS) displayed by the protein's nuclear spins. PCS are highly useful for determining the coordinates of individual spins in the molecule and for rapid structure determinations of entire protein-protein and protein-ligand complexes. However, PCS measurements require reliable resonance assignments for the molecule in its paramagnetic state and in a diamagnetic reference state. This article discusses different approaches for pairwise resonance assignments, with emphasis on a strategy which exploits chemical exchange between the two states. 相似文献
155.
156.
157.
本文对月光花素甲(Calonyctin A)的整体分子结构分析加以完善并进行总结。前文报道月光花素甲是两个分子量相差28a.m.u的糖甙类同系物分子的混合物。这两个分子(简称M_1和M_2)分别称为月光花素甲(Ⅰ)与月光花素甲(Ⅱ)(Calonyctm A_1,CalonyctinA_2),分子量分别为938与910。它们分别含 相似文献
158.
N.D. Yordanov V. Gancheva M. Radicheva B. Hristova M. Guelev O. Penchev 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1998,54(14):2413-2419
Non irradiated and γ-irradiated dry herbs savoury (Savoury), wild thyme (Thymus serpollorium) and marjoram (Origanum) with absorbed dose of 8 kGy have been investigated by the methods of elecrtron paramagnetic resonance (EPR) and thermoluminescence (TL). Non-irradiated herbs exhibit only one weak siglet EPR signal whereas in irradiated samples its intensity increase and in addition two satelite lines are recorded. This triplet EPR spectrum is attributed to cellulose free radical generated by irradiation. It has been found that upon keeping the samples under the normal stock conditions the life-time of the cellulose free radical in the examined samples is ∼60–80 days. Thus the conclusion has been made that the presence of the EPR signal of cellulose free radical is unambiguous indication that the sample under study has been irradiated but its absence can not be considered as the opposite evidence. In the case when EPR signal was absent the method of TL has been used to give the final decision about the previous radiation treatment of the sample. 相似文献
159.
本文应用取代基效应(SCS)方法研究了乙烯-乙烯醇(EVA)共聚物,得到了羟基(-OH)在两种不同溶剂中的SCS参数:在苯酚+重水(80/20W/W)中参数为S_1=42.77±0.08ppm,S_2=7.155±0.06ppm,S_3(s)=-4.08±0.02ppm,S_3(t)=-3.09±0.02ppm,S_4=0.48±0.03ppm,S_5=0.26±0.05ppm,在以邻二氯苯为溶剂时参数为S_1=44.97±0.61ppm,S_2=7.40±0.00ppm,S_3(s)=-4.51±0.17ppm,S_3(t)=-3.13±0.00ppm,S_4=0.63±0.04ppm,S_5=0.36±0.00ppm,同时利用所得到的SCS参数对该共聚物的~(13)C NMR谱进行了归属。 相似文献
160.
Tomislav P. Živković 《Theoretical chemistry accounts》1988,73(2-3):207-219
A new method for the calculation of bond orders in alternant hydrocarbons is presented. The method requires a summation over the contributions of various superposition diagrams. Quantitatively, the method is almost as reliable as PPP, and due to its simplicity it can be used for fast and relatively accurate calculation of bond orders. In addition some simple rules are derived, which in many cases can be used to predict the signs of bond orders between nonbonded atoms.Dedicated to Professor J. Koutecký on the occasion of his 65th birthdayResearch supported by the Robert A. Welch Foundation of Houston, Texas 相似文献