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21.
Il Nuovo Cimento D - Deterioration of the superconducting properties of HTC materials, induced by different substitutions, offers a key towards the understanding of the basic HTC interactions.... 相似文献
22.
Marcantoni E Roselli G Lucarelli L Renzi G Filippi A Trionfetti C Speranza M 《The Journal of organic chemistry》2005,70(10):4133-4141
[isomers: see text] The kinetics and stereochemistry of the protonation-induced unimolecular isomerization of (R)-1-D1-3-(p-fluorophenyl)butane have been investigated in the gas phase at 40-100 degrees C and 70-760 Torr. This process leads to the formation of the relevant meta and ortho isomers with partial racemization of the migrating sec-butyl moiety. Complete racemization is observed, instead, when the isomerization reaction involves a 1,2-H shift in the moving alkyl group. These results, together with the relevant activation parameters, fully confirm the previous evidence of the occurrence in the alkyl cation/arene PES of noncovalent eta-type intermediates of defined structure and stability, lying well below the classical pi-complexes, as confirmed by ab initio calculations. Their crucial role in determining the positional selectivity of gas-phase electrophilic aromatic substitutions clearly emerges from the comparison of the present results with the site selectivity measured in the corresponding bimolecular arene alkylation carried out at the same temperatures and pressures. 相似文献
23.
De Renzi V Rousseau R Marchetto D Biagi R Scandolo S Del Pennino U 《Physical review letters》2005,95(4):046804
The role of molecular dipole moment, charge transfer, and Pauli repulsion in determining the work-function change (Deltaphi) at organic-metal interfaces has been elucidated by a combined experimental and theoretical study of (CH(3)S)(2)/Au(111) and CH(3)S/Au(111). Comparison between experiment and theory allows us to determine the origin of the interface dipole layer for both phases. For CH(3)S/Au(111), Deltaphi can be ascribed almost entirely to the dipole moment of the CH(3)S layer. For (CH(3)S)(2)/Au(111), a Pauli repulsion mechanism occurs. The implications of these results on the interpretation of Deltaphi in the presence of strongly and weakly adsorbed molecules is discussed. 相似文献
24.
The reaction between mercury(II) chloride and azoles(pyrazole, 3,5-dimethylpyrazole, benzotriazole, 1,2,4-triazole) afforded mainly N-chloro mercury derivatives, although other reactions, such as the well known ring mercuration or the formation of a complex, were observed simultaneously. Therefore, no simple generalization explains the observed reactivity of azoles towards mercury(II) chloride, each reaction investigated being a different case. 相似文献
25.
Mattia Silvi Polyssena Renzi Deborah Rosato Cristiana Margarita Alessio Vecchioni Ivan Bordacchini Diego Morra Alessandro Nicolosi Riccardo Cari Dr. Fabio Sciubba Dr. Daniele M. Scarpino Schietroma Dr. Marco Bella 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(30):9973-9978
A challenging asymmetric reaction (aza‐Michael addition of imides to enones) has been optimized through an integrated approach involving the synthesis of a family of organocatalysts, multiple catalysis (usage of additives), and finally with rational exploration of the chemical space by the application of the experiment design. 相似文献
26.
S. Agrestini S. Sanna K. Zheng R. De Renzi E. Pusceddu G. Concas N.L. Saini A. Bianconi 《Journal of Physics and Chemistry of Solids》2014
We have studied the electronic structure of unoccupied states measured by O K-edge and Cu L-edge x-ray absorption spectroscopy (XAS), combined with crystal structure studied by high resolution powder x-ray diffraction (HRPXRD), of charge-compensated layered superconducting CaxLa1−xBa1.75−xLa0.25+xCu3Oy (0≤x≤0.4 and 6.4≤y≤7.3) cuprate. A detailed analysis shows that, apart from hole doping, chemical pressure on the electronically active CuO2 plane due to the lattice mismatch with the spacer layers greatly influences the superconducting properties of this system. The results suggest chemical pressure to be the most plausible parameter to control the maximum critical temperatures (Tcmax) in different cuprate families at optimum hole density. 相似文献
27.
Corradini V Biagi R del Pennino U De Renzi V Gambardella A Affronte M Muryn CA Timco GA Winpenny RE 《Inorganic chemistry》2007,46(12):4937-4943
A study of the deposition of heterometallic antiferromagnetically coupled rings onto gold surfaces is reported. Two new {Cr7Ni} rings, [NH2nPr2][Cr7NiF8(3-tpc)16] (1) (where 3-tpc=3-thiophenecarboxylate) and [nBuNH2CH2CH2SH] [Cr7NiF8(O2CtBu)16] (2) have been made and structurally characterized. They have been deposited from the liquid phase on Au(111) and the adsorbed molecules compared by means of scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS). In both cases a two-dimensional distribution of individually accessible {Cr7Ni} heterometallic rings on the gold surface has been obtained, exploiting the direct grafting of sulfur-functionalized clusters. There is a competition between the chemisorption of the {Cr7Ni} clusters and a thiolic self-assembled monolayer (SAM) formed by free ligands. In 2, the presence of a single sulfur ligand should force the molecule to graft with the ring axis normal to the surface. The cluster stability in the STM images and the S-2p energy positions demonstrate, for both functionalizations, the strength of the grafting with the gold surface. 相似文献
28.
Filippi A Giardini A Marcantoni E Paladini A Piccirillo S Renzi G Rondino F Roselli G Satta M Speranza M 《Physical chemistry chemical physics : PCCP》2007,9(14):1676-1679
The R2PI-TOF spectra of supersonically expanded rare gas/chiral arene heteroclusters have been rationalized in terms of the distortion of the pi-electron density reflecting the different dipole and quadrupole momenta induced in the rare gas atoms by interaction with the opposite pi-faces of the chiral arene itself. 相似文献
29.
Asymmetric organocatalysis is now an established methodology for the preparation of chiral compounds. However, these are not the only valuable molecules which can be conveniently obtained. Organocatalytic reactions affording achiral compounds are gaining momentum, opening unexplored pathways in the synthesis of densely functionalized aromatic moieties, olefins and useful molecules such as natural substances. 相似文献
30.