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1.
Marilyn Breen 《Journal of Geometry》1989,36(1-2):8-16
LetS be a compact, simply connected set inR
2. If every boundary point ofS is clearly visible viaS from at least one of the three pointsa, b, c, thenS is a union of three starshaped sets whose kernels containa, b, c, respectively. The result fails when the number three is replaced by four.As a partial converse, ifS is a union of three starshaped sets whose kernels containa, b, c, respectively, then the set of points in the boundary ofS clearly visible from at least one ofa, b, orc is dense in the boundary ofS.Supported in part by NSF grant DMS-8705336. 相似文献
2.
Marilyn M. Olmstead James C. Fettinger Soya Gamsey Jacob W. Clary Bakthan Singaram 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(6):o333-o335
The structures of three chiral vinyldioxazaborocanes are reported, namely (2E)‐ and (2Z)‐6‐benzyl‐2‐buten‐2‐yl‐1,3,6,2‐dioxazaborocane, C27H30BNO2, (II) and (III), respectively, and (2Z)‐2‐buten‐2‐yl‐6‐isobutyl‐1,3,6,2‐dioxazaborocane, C24H32BNO2, (IV). These compounds may be useful in asymmetric reactions. In the structures reported here, the N—B donor–acceptor bond is longer than in any previously reported analogous compounds. 相似文献
3.
In a previous paper, some 15 compounds were positively identified among the products of thermal degradation of bisphenol-A diglycidyl ether. The structures of an additional 22 compounds, all aromatic, were speculated upon on the basis of mass spectral analysis. In the present paper, mechanisms are proposed to account for all these products and the characteristics of their formation in the overall degradation process. 相似文献
4.
Sammelson RE Gurusinghe CD Kurth JM Olmstead MM Kurth MJ 《The Journal of organic chemistry》2002,67(3):876-882
An efficient and selective method for the synthesis of spiro-fused (C5)-isoxazolino-(C4)-pyrazolones (C) is reported. The process consists of utilizing the Baylis-Hillman reaction-or a quicker, stepwise MAC procedure-to give I followed by 1,3-dipolar cycloaddition and Swern oxidation to give beta-ketoesters H, which were condensed with hydrazine derivatives to provide hydrazones that underwent cycloelimination. These novel spiro-fused (C5)-isoxazolino-(C4)-pyrazolones were confirmed by spectroscopic analysis as well as single-crystal X-ray of 5. We also concluded that all condensations/cycloeliminations, except with hydrazine itself, were more effective with catalysts or higher reaction temperatures. For example, TiCl(4) was an efficient catalyst for hydrazone formation and cycloelimination with methylhydrazine, while phenyl-, benzyl-, and (4-methoxyphenyl)hydrazine reacted effectively without catalyst in refluxing xylene. 相似文献
5.
Cui C Brynda M Olmstead MM Power PP 《Journal of the American Chemical Society》2004,126(21):6510-6511
Reaction of Ar'GeGeAr' (1) with an excess of Me3SiN3 gives the non-Kekulé, biradicaloid Ar'Ge(mu-NSiMe3)2GeAr' (3, Ar' = 2,6-Dipp2C6H3, Dipp = 2,6-i-Pr2C6H3) which has a planar Ge2N2Si2 array and pyramidal geometry at the germaniums. DFT calculations for the model MeGe(mu-NSiH3)2GeMe indicate no Ge-Ge bonding and a singlet ground state. The calculated energy difference between the optimized singlet and triplet states is 17.51 kcal/mol. 相似文献
6.
Monoanionic tridentate ligands LHa and LHb containing ONSe and ONTe donor sequences and their Pd2+ and Pt2+ derivatives were synthesized and characterized. The formation of a five- and a six-membered ring around the central metal atom and associative phenomena in solutions provide extra stability to the metal complexes. 相似文献
7.
Harrop TC Olmstead MM Mascharak PK 《Journal of the American Chemical Society》2004,126(45):14714-14715
The Ni(II)-dicarboxamido-dithiolato complexes (Et4N)2[Ni(NpPepS)] (1) and (Et4N)2[Ni(PhPepS)] (2) were used as Nid metallosynthons in the construction of higher nuclearity dinuclear Ni-Cu and Ni-Ni species to model the bimetallic Mp-Nid site of the A-cluster of acetyl coenzyme A synthase/CO dehydrogenase (ACS/CODH). Reaction of 1 with [Cu(neo)Cl] and [Ni(terpy)Cl2] in MeCN affords the dinuclear complexes (Et4N)[Cu(neo)Ni(NpPepS)] (3) and [Ni(terpy)Ni(NpPepS)] (4), respectively. Reaction of 2 with [Ni(dppe)Cl2] in MeCN yields [Ni(dppe)Ni(PhPepS)] (6). The Ni-Cu complex 3 exhibits no redox chemistry at the Nid site and no reaction with CO. In contrast, the Nip sites in 4 and 6 are readily reduced (characterized by their Ni(I) EPR spectra) and bind CO, exhibiting nuco bands at 2044 and 1997 cm-1, respectively, indicating terminal CO binding. The present Ni-Ni systems replicate the structural and chemical properties of the A-cluster site in ACS/CODH and support the presence of Ni at Mp in the catalytically active enzyme. 相似文献
8.
Colorless [Au[C(NHMe)(2)](2)]X.H(2)O (X = Cl or Br) crystallize as dimers with Au.Au separations of 3.1231(3) A (Cl salt) and 3.1297(4) A (Br salt) between the linear, two-coordinate cations, and there is no direct interaction of Au(I) with the halide ions which are hydrogen bonded to ligand N-H groups and the water molecules. The luminescence of these dimers occurs at higher energy than that observed in extended chains of the same cation in the corresponding (PF(6))(-) and (BF(4))(-) salts and shows the important effects of aggregation on the observed luminescence. 相似文献
9.
The results presented here show that the nature of the axial ligand can alter the distribution of electrons between the metal and the porphyrin in complexes where there is an oxygen atom replacing one of the meso protons. The complexes (1-MeIm)(2)Fe(III)(OEPO) and (2,6-xylylNC)(2)Fe(II)(OEPO(*)) (where OEPO is the trianionic octaethyloxophlorin ligand and OEPO(*) is the dianionic octaethyloxophlorin radical) were prepared by addition of an excess of the appropriate axial ligand to a slurry of [Fe(III)(OEPO)](2) in chloroform under anaerobic conditions. The magnetic moment of (2,6-xylylNC)(2)Fe(II)(OEPO(*)) is temperature invariant and consistent with a simple S = (1)/(2) ground state. This complex with an EPR resonance at g = 2.004 may be considered as a model for the free-radical like EPR signal seen when the meso-hydroxylated heme/heme oxygenase complex is treated with carbon monoxide. In contrast, the magnetic moment of (1-MeIm)(2)Fe(III)(OEPO) drops with temperature and indicates a spin-state change from an S = (5)/(2) or an admixed S = (3)/(2),(5)/(2) state at high temperatures (near room temperature) to an S = (1)/(2) state at temperatures below 100 K. X-ray diffraction studies show that each complex crystallizes in centrosymmetric form with the expected six-coordinate geometry. The structure of (1-MeIm)(2)Fe(III)(OEPO) has been determined at 90, 129, and 296 K and shows a gradual and selective lengthening of the Fe-N(axial bond). This behavior is consistent with population of a higher spin state at elevated temperatures. 相似文献
10.
Solvent effects on the electrochemistry and spectroscopic properties of alkyl- and aryl-substituted corroles in nonaqueous media are reported. The oxidation and reduction of six compounds containing zero to seven phenyl or substituted phenyl groups on the macrocycle were studied in four different nonaqueous solvents (CH(2)Cl(2), PhCN, THF, and pyridine) containing 0.1 M tetra-n-butylammonium perchlorate. Dimers were formed upon oxidation of all corroles in CH(2)Cl(2), but this was not the case in the other three solvents, where either monomers or dimers were formed upon oxidation depending upon the solvent Gutmann donor number and the number or location of aryl substituents on the macrocycle. The half-wave potentials were analyzed as a function of the number of aryl substituents on the macrocycle as well as the concentration of added pyridine to PhCN solutions of the compound, and these data were combined with data from the spectroelectrochemistry experiments to determine the stoichiometry of the species actually in solution after the first oxidation or first reduction of each compound. The results of these experiments indicate that reduction of the bispyridine adduct (Cor)Co(III)(py)(2) proceeds via the monopyridine complex (Cor)Co(III)(py) to give in each case the unligated cobalt(II) corrole [(Cor)Co(II)](-). In contrast, pyridine remains coordinated after electrooxidation, and the final product was characterized as [(Cor)Co(III)(py)(2)](+). 相似文献