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41.
SCF-MO studies as FeS, CrS and ZnS illustrate the changing role ofd-orbitals along a transition series, where they become at first good acceptors playing an important role in the bonding, then so stable that their electrons behave essentially as “core” electrons in agreement with the conjecture of Phillips and Williams [1]. 相似文献
42.
Charles M. MarsonJane McGregor Timothy WalsgroveTrevor J. Grinter Harry Adams 《Tetrahedron letters》2003,44(1):141-143
Treatment of an unsaturated 2,3-epoxy alcohol with SnBr4 leads to a stereoselective formation of a cyclopropane ring, and an α-ketol unit as part of a subsequent ring expansion. 相似文献
43.
Thitivat Suebsaeng Charles A. Wilkie Vern T. Burger Janet Carter Charles Eric Brown 《Journal of polymer science. Part A, Polymer chemistry》1984,22(4):945-957
The solid reaction products from pyrolysis of polyethylene terephthalate in the presence and absence of red phosphorus were characterized by CP/MAS 13C-NMR, FR-IR, and MAS 31P-NMR spectroscopy. Over the temperature range of 300–400°C, polyethylene terephthalate was converted in a sealed vial to a highly crosslinked polymer of terephthalic acid. Pyrolysis in the presence of red phosphorus, which functions as a flame retardant by increasing the amount of char, yielded an intractible polyaromatic phosphate ester. After thermal cleavage of polyethylene terephthalate with formation of free carboxyl and vinyl ester groups, there are two competing reaction pathways. The smaller molecular weight fragments may enter the vapor phase where they undergo further degradation primarily to CO2, CO, and acetaldehyde, as described by others. However, if volatilization of the oligomeric fragments is inhibited, an alternate reaction pathway gives rise to the formation of highly crosslinked char. Red phosphorus decreases the volatility of the oligomeric fragments by converting them to phosphates and thereby enhances char formation. 相似文献
44.
The adsorption of lipoteichoic acid onto the surface of titanium dioxide is shown to be heterogeneous. 31P CPMAS solid-state NMR reveals two distinct phosphate species. The chemical shift anisotropy, asymmetry parameter, and rotating-frame spin-lattice relaxation suggest that 50% of the phosphates are bound to the surface. The remaining phosphates also exhibit restricted molecular motion, but do not have a direct surface bond. 相似文献
45.
Charles C. Wu Robert W. Lenz 《Journal of polymer science. Part A, Polymer chemistry》1972,10(12):3555-3567
The thermal ring-opening reactions, autoxidation and hydrogenation of polymethy-lenecyclobutene (PMCB) and poly-1-methyl-3-methylenecyclobutene (PMMCB), were investigated. Both polymers were prepared by cationic polymerization and consisted almost entirely of 1,5-repeating units containing cyclobutene rings in the polymer backbone. Both polymers showed well behaved exothermic processes at elevated temperatures which apparently resulted in crosslinking. These processes were investigated by differential scanning calorimetry and interpreted to involve thermal ring-opening reactions. Autoxidation occurred very rapidly in PMCB but much more slowly in PMMCB as predicted by Bolland's rules. Attempts to hydrogenate the cyclobutene rings in both polymers resulted in the occurrence of hydrogenolysis in PMCB and little or no reaction with PMMCB for a Pd-catalyzed reaction and partial hydrogenation of the latter for a diimide reaction. 相似文献
46.
Charles E. Reid 《International journal of quantum chemistry》1972,6(2):383-386
It is a standard theorem of group representation theory that the dimension of an irreducible representation is a divisor of the order of the group. This paper gives a new, relatively simple proof, intended to make the theorem understandable to readers unfamiliar with algebraic integers. 相似文献
47.
Charles S. Kahane 《Integral Equations and Operator Theory》1984,7(1):96-117
The integral operator which sends f (ζ) into $$\int_{|\xi |< 1} {\tfrac{{f(\xi )}}{{|x - \xi |^{p - 1} }}} d\xi = g(x)(|x|< 1)$$ x and ζ ∈ RP, is shown to map the space of functions f (ζ) on |ζ|<1, square integrable with respect to the weight (1-|ξ|2)1/2 one to one onto the space of functions g (x) on |x|<1 which possess gradients δg(x) in the sense of distribution theory, with both g(x) and δg(x) being square integrable with respect to the weight (1-|x|2)1/2. This extends to p≥3 a result of P. Wolfe's in the case p=2. 相似文献
48.
Joachim Schaefer William A. Lester Donald Kouri Charles A. Wells 《Chemical physics letters》1974,24(2):185-190
Integral cross sections for pure rotational and vibrational-rotational excitation of H2(X1Σ+g) by Li+(1S) impact are computed by close-coupling methods at 0.2, 0.6, and 1.2 eV in the c.m. system using vibrational functions that are numerical solutions of the one-dimensional radial Schrödinger equation for harmonic, Morse, and adiabatically corrected Kolos-Wolniewicz (KW) potential functions. Comparison of results employing KW and Morse functions shows excellent agreement for all transitions studied. Findings using harmonic oscillator functions, however, differ noticeably from KW and Morse values for vibrational (0 → 1) and very large rotational (Δj = 10) transitions, but are satisfactory for lower order (0 → 2, 4, 6, 8) rotational transitions. 相似文献
49.
Charles O. Okafor 《Journal of heterocyclic chemistry》1976,13(1):107-110
The reactions of 2-amino-3-hydroxypyridine and 2-chloro-3-nitropyridine in various solvents and in the presence of certain catalysts were studied. A dilute acid-catalysed procedure led to a 45% yield of 3-hydroxy-3-nitro-2,2-dipyridylamine which was also obtained by refluxing in alcoholic potassium hydroxide for several hours. The diarylamine was converted to 1,9-diazaphenoxazine by base-catalysed intramolecular condensation in refluxing DMSO. The same diazaphenoxazine was obtained directly by prolonged base-catalysed reaction of the starting pyridine compounds in DMSO. From a study of the infrared spectrum of the diarylamine precursor, it was found that strong NHO hydrogen bonding is responsible for the failure of the cyclization step in either aqueous or alcoholic base. This problem was overcome by the use of DMSO as the reaction solvent. Structural assignments were made by a study of their ultraviolet, infrared, nmr and mass spectra and the mechanistic pathways were also discussed. 相似文献
50.
Goldschmidt RJ Wetzel SJ Blair WR Guttman CM 《Journal of the American Society for Mass Spectrometry》2000,11(12):1095-1106
Various secondary series are observed in matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectra of polystyrene. The number and positions of the series depend on the choice of matrix and added cation. For a given treatment, series observed in linear mode are not necessarily observed in reflectron mode, and vice versa. Post-source decay analysis was used to determine that the secondary series arise at least in part from formation and decay of adducts of polystyrene with matrix species. There is some treatment-to-treatment variation, but adduct formation and decay were observed for all tested treatments. The multiplicity of secondary series makes it unclear whether post-source decay occurs for the main series (polystyrene + cation)+ ions under the conditions normally used for polystyrene analysis. Such ions do undergo post-source decay at laser fluences greater than normally used. Although only polystyrene was investigated in this work, other polymers may also produce adduct and decay series in MALDI analysis. Their presence can mask the presence of minor components in a sample, but at least as observed here, do not have a strong influence on molecular mass determinations. 相似文献