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排序方式: 共有81条查询结果,搜索用时 31 毫秒
1.
Edwin Haselbach Urs Klemm Rudolf Gschwind Thomas Bally Laurant Chassot Stephan Nitsche 《Helvetica chimica acta》1982,65(8):2464-2471
The radical cations of indeno [2, 1-a]indene ( 1 ), stilbene ( 2 ) and 3, 5, 3', 5'-tetramethylstilbene ( 3 ) were prepared by γ-irradiation of the neutral precursors in an electron-scavenging matrix at 77 K . Their electronic spectra were recorded and compared to the photoelectron spectra ( PE .) of the neutral precursors. The results show that either the fourth or the fifth excited doublet state of the cations is of «Non-Koopmans» type, with specific doublet energy (D) D (2Bg)=2.74 eV ( 1 +), =2.59 eV ( 2 +), =2.49 eV ( 3 +). Remarkably, 1 + possesses two electronic states in the 2.7-2.8 eV energy range: 2Au («Koopmans»-type) and 2Bg («Non -Koopmans»-type). The «SDT»-equation \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm D} = \sqrt {{\rm S} \cdot {\rm T}} $\end{document} approximately connecting excited singlet (S) and triplet (T) states of a neutral alternant system with the excited doublet (D) states of its radical cation - provided e-promotion occurs For all three excited states between the same (paired) orbitals-is satisfyingly exemplified by 1 : S1 = 3.92 eV and T1= 2.06 eV for 1 , D4 or 5=2.74 eV for 1 +. 相似文献
2.
Gschwind RM Armbrüster M Zubrzycki IZ 《Journal of the American Chemical Society》2004,126(33):10228-10229
Hydrogen bonding plays a major role in the selective recognition of guanidinium groups by receptor molecules. The present NMR investigation provides direct experimental evidence of hydrogen bonds in an artificial arginine receptor complex consisting of alpha-N-benzoylarginine ethyl ester and a bisphosphonate tweezers molecule. trans-Hydrogen bond 2hJHP couplings between the phosphonate moieties and individual guanidinium protons as well as the amide proton have been detected by [1H,31P]-HMBC and [31P,1H]-INEPT experiments. The detected hydrogen bonding network in the investigated artificial arginine receptor shows a symmetrical end-on interaction of the guanidinium moiety, which enables concerted rotations and deviates from the structure proposed for the biological arginine fork. 相似文献
3.
The kinetics of the formation of the photochromic forms B and C of tetramethyl-dianthrone has been studied in triacetin and methylcyclohexane/2-methylpentane at several temperatures. A flash spectroscopy method was developed, which allows the recording of the transient behaviour of the sample as function of both – wavelength and time – using a single photoflash for excitation. The results show that the photochromic forms B and C are directly populated from the excited singlet state. In addition a new triplet-triplet absorption band in the near infrared region was detected. 相似文献
4.
Binary intercluster compounds (IC) can be reduced to basic structure types of ionic solids. We examined the validity of this concept for ternary compounds, on the example of a quasi-ternary intercluster compound made from a Keggin anion ([PMo12O40]3?), an organic cation (o-xylylenebis(triphenylphosphonium)), and a complex (cobaltocenium). The new compound and its two related quasi-binary IC were investigated by X-ray diffractometry, examined for intermolecular interactions such as hydrogen-bonding, π–, or van der Waals-interactions, and evaluated for possible reductions to basic structure types. 相似文献
5.
6.
Franziska Pecho Dr. You-Quan Zou Johannes Gramüller Prof. Dr. Tadashi Mori Prof. Dr. Stefan M. Huber Dr. Andreas Bauer Prof. Dr. Ruth M. Gschwind Prof. Dr. Thorsten Bach 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(23):5190-5194
A chiral phosphoric acid with a 2,2’-binaphthol core was prepared that displays two thioxanthone moieties at the 3,3’-position as light-harvesting antennas. Despite its relatively low triplet energy, the phosphoric acid was found to be an efficient catalyst for the enantioselective intermolecular [2+2] photocycloaddition of β-carboxyl-substituted cyclic enones (e.r. up to 93:7). Binding of the carboxylic acid to the sensitizer is suggested by NMR studies and by DFT calculations to occur by means of two hydrogen bonds. The binding event not only enables an enantioface differentiation but also modulates the triplet energy of the substrates. 相似文献
7.
8.
Jitka Daďová Susanne Kümmel Christian Feldmeier Jana Cibulková Dr. Richard Pažout Dr. Jaroslav Maixner Prof. Dr. Ruth M. Gschwind Prof. Dr. Burkhard König Dr. Radek Cibulka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(3):1066-1075
A series of 10‐arylflavins (10‐phenyl‐, 10‐(2′,6′‐dimethylphenyl)‐, 10‐(2′,6′‐diethylphenyl)‐, 10‐(2′,6′‐diisopropylphenyl)‐, 10‐(2′‐tert‐butylphenyl)‐, and 10‐(2′,6′‐dimethylphenyl)‐3‐methylisoalloxazine ( 2 a – f )) was prepared as potentially nonaggregating flavin photocatalysts. The investigation of their structures in the crystalline phase combined with 1H‐DOSY NMR spectroscopic experiments in CD3CN, CD3CN/D2O (1:1), and D2O confirm the decreased ability of 10‐arylflavins 2 to form aggregates relative to tetra‐O‐acetyl riboflavin ( 1 ). 10‐Arylflavins 2 a – d do not interact by π–π interactions, which are restricted by the 10‐phenyl ring oriented perpendicularly to the isoalloxazine skeleton. On the other hand, N3? H???O hydrogen bonds were detected in their crystal structures. In the structure of 10‐aryl‐3‐methylflavin ( 2 f ) with a substituted N3 position, weak C? H???O bonds and weak π–π interactions were found. 10‐Arylflavins 2 were tested as photoredox catalysts for the aerial oxidation of 4‐methoxybenzyl alcohol to the corresponding aldehyde (model reaction), thus showing higher efficiency relative to 1 . The quantum yields of 4‐methoxybenzyl alcohol oxidation reactions mediated by arylflavins 2 were higher by almost one order of magnitude relative to values in the presence of 1 . 相似文献
9.
P. I. Demyanov P. M. Polestshuk V. S. Petrosyan R. Gschwind 《Russian Chemical Bulletin》2008,57(3):480-492
The structures of monomeric lithium dimethylcuprate solvated by three 1,2-dimethoxyethane (DME) molecules (Me2Cu)Li · 3DME and its oligomers [(Me2Cu)Li · 3DME]
n
(n = 2–5) in the gas phase were studied using the density functional theory. The structures of these systems are compared with
that of (Me2Cu)Li · 3DME in the crystal. It is shown that numerous C-H…Cu and C-H…C hydrogen bonds, as well as C-H…H dihydrogen bonds
between DME molecules, which solvate lithium cations, and corresponding dimethylcuprate anions significantly affect the formation
and structure of these compounds in the gas and solid phases.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 470–481, March, 2008. 相似文献
10.
Dr. Ravi Yadav Martin Weber Dr. Akhil K. Singh Luca Münzfeld Johannes Gramüller Prof. Dr. Ruth M. Gschwind Prof. Dr. Manfred Scheer Prof. Dr. Peter W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(56):14128-14137
A series of molecular group 2 polyphosphides has been synthesized by using air-stable [Cp*Fe(η5-P5)] (Cp*=C5Me5) or white phosphorus as polyphosphorus precursors. Different types of group 2 reagents such as organo-magnesium, mono-valent magnesium, and molecular calcium hydride complexes have been investigated to activate these polyphosphorus sources. The organo-magnesium complex [(DippBDI−Mg(CH3))2] (DippBDI={[2,6-iPr2C6H3NCMe]2CH}−) reacts with [Cp*Fe(η5-P5)] to give an unprecedented Mg/Fe-supramolecular wheel. Kinetically controlled activation of [Cp*Fe(η5-P5)] by different mono-valent magnesium complexes allowed the isolation of Mg-coordinated formally mono- and di-reduced products of [Cp*Fe(η5-P5)]. To obtain the first examples of molecular calcium-polyphosphides, a molecular calcium hydride complex was used to reduce the aromatic cyclo-P5 ring of [Cp*Fe(η5-P5)]. The Ca-Fe-polyphosphide is also characterized by quantum chemical calculations and compared with the corresponding Mg complex. Moreover, a calcium coordinated Zintl ion (P7)3− was obtained by molecular calcium hydride mediated P4 reduction. 相似文献