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21.
22.
Maria A. Curtin Irwin A. Taub Kenneth Kustin Narith Sao Jeremy R. Duvall Katharine I. Davies Christopher J. Doona Edward W. Ross 《Research on Chemical Intermediates》2004,30(6):647-661
The slow reaction between peroxodisulfate and formate is significantly accelerated by ascorbate at room temperature. The products of this induced oxidation, CO2 and oxalate (C2O2–
4), were analyzed by several methods and the kinetics of this reaction were measured. The overall mechanism involves free radical species. Ascorbate reacts with peroxodisulfate to initiate production of the sulfate radical ion (SO–
4), which reacts with formate to produce carbon dioxide radical ion (CO–
2) and sulfate. The carbon dioxide radical reacts with peroxodisulfate to form CO2 or self-combines to form oxalate. Competition occurring between these two processes determines the overall fate of the carbon dioxide radical species. As pH decreases, protonation of the carbon dioxide radical ion tends to favor production of CO2. 相似文献
23.
The synthesis and transition temperatures of some trans-4-alkylcyclohexylethyl-substituted 2,3-difluorobiphenyls 总被引:1,自引:0,他引:1
Terphenyls with two lateral ortho-fluoro-substituents have proved to be excellent host materials for ferroelectric (SC*) mixtures. The compounds reported here are biphenyls with the same arrangement of lateral substituents but with a trans-4-alkylcyclohexylethyl moiety as one of the terminal substituents. Such three ring systems retain the ability to generate the SC mesophase and have low melting points. Low temperature lithiation procedures were used to prepare phenylboronic acids, which were then used in palladium catalysed cross-coupling procedures to prepare the desired compounds. The effect of molecular structure on the mesophase types and thermal stabilities is discussed and comparisons are made with analogous terphenyls and biphenyls with open chain terminal substituents. 相似文献
24.
25.
Walstrom A Pink M Yang X Tomaszewski J Baik MH Caulton KG 《Journal of the American Chemical Society》2005,127(15):5330-5331
Replacement of chloride in (PNP)RuCl, PNP = (tBu2PCH2SiMe2)2N, by Me3SiN3 gives a pre-redox adduct that, already at -30 degrees C, releases N2 to produce the mononuclear nonplanar Ru(IV) nitride (PNP)RuN, characterized by spectroscopic and X-ray methods. DFT calculations show the planar structure to be only 1.6 kcal/mol less stable, which explains the time-averaged simplicity of the 1H NMR spectrum, as well as the large vibrational amplitude of the nitride ligand. 相似文献
26.
The synthesis of 2-methyl-5H-dibenz[b,f]azepine-5-carboxamide (2-methylcarbamazepine, 2-MCBZ, 8), a promising internal standard for chromatographic assays of the antiepileptic agent carbamazepine (CBZ, 1), is described. N-(p-Tolyl)anthranilic acid (2) was utilized as a starting material for the synthesis of a key compound, 2,9-dimethylacridine (4), which was converted in two steps to 2-methyl-9-hydroxymethylacridan (6). The acridan 6, in the presence of poly-phosphoric acid, was ring-expanded to form 2-methyl-5H-dibenz[b,f]azepine (7), this latter compound being converted by conventional reactions to its 5-carbamyl derivative, 2-MCBZ (8). 相似文献
27.
Derivatization of a variety of peptides by a method known to enhance anhydride formation is demonstrated by mass spectrometry to yield ions that have elemental composition and fragmentation properties identical to [b(n-1) + OH + H]+ ions formed by gas-phase rearrangement and fragmentation. The [b(n-1) + OH + H]+ ions formed by gas-phase rearrangement and fragmentation and the solution-phase [b(n-1) + OH + H]+ ion structural analogs formed by derivatization chemistry show two different forms of dissociation using multiple-collision CAD in a quadrupole ion trap and unimolecular decomposition in a TOF-TOF; one group yields identical product ions as a truncated form of the peptide with a free C-terminal carboxylic acid and fragments at the same activation energy; the other group fragments differently from the truncated peptide, being more resistant to fragmentation than the truncated peptide and yielding primarily the [b(n-2) + OH + H]+ product ion. Nonergodic electron capture dissociation MS/MS suggests that any structural differences between the specific-fragmenting [b(n-1) + OH + H]+ ions and the truncated peptide is at the C-terminus of the peptide. The specific-fragmentation can be readily observed by MS(n) experiments to occur in an iterative fashion, suggesting that the C-terminal structure of the original [b(n-1) + OH + H]+ ion is maintained after subsequent rearrangement and fragmentation events in peptides which fragment specifically. A mechanism for the formation of specific-fragmenting and nonspecific-fragmenting [b(n-1) + OH + H]+ ions is proposed. 相似文献
28.
Polymers and plastics are receiving increased attention as materials for microfluidics and microTAS applications. Given the ubiquity of fluorescence detection techniques in micro-analytical systems, the fluorescence properties of polymers and plastics should not be overlooked. We survey some commonly available polymer thin-films for their fluorescence behaviour under standardized conditions to determine which materials are most suitable for high-sensitivity fluorescence detection lab chips. The initial fluorescence intensities of some of the materials surveyed were significantly higher than glass and fused silica controls, and decreased over the three hour period with complex kinetics. We then discuss how this has confounded fluorescence detection in our analytical context, and possible mechanisms for the decrease. 相似文献
29.
Kenneth R. Seddon 《Journal of organometallic chemistry》1985,293(1):C21-C25
A close examination of the ESR spectrum of a paramagnetic complex formed from bis(ethoxythiocarbonyl)sulfide and dimanganese decacarbonyl has revealed, for the first in this type of radical adduct, 13C hyperfine coupling in natural abundance from the carbonyl ligands. 相似文献
30.
Rijssenbeek JT Saito T Malo S Azuma M Takano M Poeppelmeier KR 《Journal of the American Chemical Society》2005,127(2):675-681
The related parameters of cation size and valence that control the crystallization of Sr(3)CaRu(2)O(9) into a 1:2 B-site-ordered perovskite structure were explored by cationic substitution at the strontium and calcium sites and by the application of high pressure. At ambient pressures, Sr(3)MRu(2)O(9) stoichiometries yield multiphasic mixtures for M = Ni(2+), Mg(2+), and Y(3+), whereas pseudocubic perovskites result for M = Cu(2+) and Zn(2+). For A-site substitutions, an ordered perovskite structure results for Sr(3-x)Ca(x)CaRu(2)O(9), with 0 = x = 1.5. In contrast, Ba(2+) substitution for Sr(2+) is accompanied by a phase change to a hexagonal BaTiO(3) structure type. At high pressures and temperatures, a 1:2 B-site-ordered perovskite structure is stabilized for Sr(3-x)Ba(x)CaRu(2)O(9), with 0 = x = 3. The scarcity of B-site-ordered perovskite ruthenates at ambient pressure and the metastable nature of the high-pressure phases underscore the strict size and valence requirements that must be met by the constituent cations to achieve these uncommon ordered structures. 相似文献