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991.
Dimethylcarbonate (DMC) is a valuable methylating reagent that can replace methyl halides and dimethylsulfate in the methylation of a variety of nucleophiles. It couples tunable reactivity and unprecedented selectivity towards mono-C- and mono-N-methylation. In addition, it is a prototype example of a green reagent, because it is nontoxic, is made by a clean process, is biodegradable, and reacts in the presence of a catalytic amount of base, thereby avoiding the formation of undesirable inorganic salts as by-products. Depending on the reaction conditions, DMC can be reacted under plug-flow, CSTR, or batch conditions. Other remarkable reactions are those where DMC behaves as an oxidant. The reactivity of other carbonates is reported as well. 相似文献
992.
M. Srividhya 《European Polymer Journal》2006,42(10):2743-2754
A series of novel poly(imide-siloxane)s (PIS) were synthesized by the grafting of amine terminated soluble imides to the siloxane backbone. The amine terminated imides were synthesized by choosing suitable anhydrides and amines to get the imides that are soluble in polar and non-polar solvents. The imides were grafted to the siloxane backbone by the epoxy group cleavage. All the polymers were obtained in quantitative yields with the inherent viscosities ranging from 0.22 to 1.2 dL g−1. The polymers were characterized by FT-IR, 1H and 13C NMR, and were examined for their thermal properties. The polymers were found to be stable up to a temperature 350 °C. The DSC results showed a single glass transition in the negative temperature, whereas the DTA revealed another glass transition in the positive end for some of the polymers showing phase separation. Polymer films were prepared employing the coupling reaction between PIS and the polydimethylsiloxane matrix by varying the amount of incorporation of PIS in the films. The polymer films had a tensile strength of 35-82 MPa with a percentage elongation of 86-271%. The contribution of polar and dispersion component towards the total surface energy was studied by the contact angle measurement and a reduction in surface tension of 14 mN m−1 was achieved with the fluorine containing PIS membrane. 相似文献
993.
Free-energy-perturbation theory from molecular dynamics calculations has been used to obtain the DeltaG of adjoining cavities' formation in water. The DeltaGs for systems with three, five and seven cavities are compared with that of a single cavity of the same volume, and found to be in good agreement. The conditions under which the analytical formulation of the energy of cavity formation proposed by Pierotti holds are discussed. The data for a single cavity have been tabulated and can lend themselves to a simple numerical implementation in standard quantum chemical packages, which can be used when high accuracy for DeltaG(cav) is required. 相似文献
994.
Xiao Lian Zhang Joseph T. Hupp Gerald D. Danzer 《Journal of Electroanalytical Chemistry》1995,380(1-2)
The comparative interfacial oxidation kinetics of the approximate structural isomers trans-(O)2ReV(py)+4 and cis-(O)2ReV(bpy)(py)+2 (py, pyridine; bpy, 2,2′-bipyridine) have been assessed in aqueous solution via conventional cyclic voltammetry at a highly ordered pyrolytic graphite (HOPG) electrode. HOPG was employed because of its known propensity to diminish interfacial electron transfer (ET) rates (by ca. three to four orders of magnitude) and because of a probable lack of importance of kinetic work terms (diffuse double-layer corrections). Measured rates for the trans complex exceed those for the cis by about a factor of 3. Expressed as an effective activation Gibbs energy difference ΔG*, this corresponds to a cis-trans difference of ca. 3 kJ mol−1. The actual vibrational barriers to ET have determined from a combination of published X-ray structural results (trans complex) and new resonance Raman results (cis complex). The values are 0.6 kJ mol −1 for the trans oxidation and 4.4 kJ mol−1 for the cis oxidation (i.e. close to the barrier difference inferred from rate measurements). Further analysis shows that most of the barrier difference is associated with displacement of a (predominantly) Re-N(bpy) stretching mode found only in the cis system. Differences in metal-oxo displacements (cis > trans) are also implicated. 相似文献
995.
Based on building emerging engineering education of "energy chemistry", we investigated the state key petro-chemical enterprises according to the industrial development and the demand of professional talents. The research report summarizes, analyzes and discusses the current priority development fields of industry, the talent training status, curriculum structure and education program of the chemistry and chemical engineering in universities. The ideas on emerging engineering education of "energy chemistry" have been proposed, and it will be beneficial to building a novel education program for talents training, which integrates the principle of chemistry, energy conversion and information science, etc. 相似文献
996.
Ivan Gutman 《Monatshefte für Chemie / Chemical Monthly》1989,120(12):1043-1047
Summary The recently proposed statistical method for the calculation of resonance energies in the conjugated circuit theory is tested on the example of polyacenes. It is found that for the estimation of the resonance energy with a 10% average error, the method requires a sample consisting of about 20 (randomly chosen) Kekulé structures. Further increase of the sample size gives no significant gain in the accuracy of the method.
Überprüfung der statistischen Methode in der Konjugierten-Ring-Theorie
Zusammenfassung Die unlängst vorgeschlagene statistische Methode in der Konjugierten-Ring-Theorie (conjugated circuit theory) wird am Beispiel der Polyacene getestet. Es wurde festgestellt, daß für die Abschätzung der Resonanzenergien bei einem mittleren Fehler von 10% für diese Methode ungefähr 20 (willkürlich gewählte) Kekulé-Strukturen nötig sind. Weitere Erhöhung dieser Anzahl bringt keine signifikante Verbesserung der Genauigkeit der Methode.相似文献
997.
998.
The potential energy surfaces for the butoxy radical dissociation into R·+O on the six low-lying electronic states have been determined with the combined CASSCF and MR-CI methods. The isomerization reactions between the different conformers of 1- and 2-butoxy radicals at the X and B states have been also investigated with the MP2, B3LYP, and CASSCF methods. The non-radiative decay mechanisms of butoxy radicals at the B state have been characterized with the computed potential energy surfaces and intersections. Supported by recent LIF experimental results, it was predicted that the t-butoxy radical would predissociate via the B/C intersection. As to 1- and 2-butoxy radicals, the relative energies of the transition states for the isomerization reactions between conformers at the B state are much lower than those of the B/C intersections, resulting in the predominance of the isomerization in the decay of the B state for 1- and 2-butoxy radicals. 相似文献
999.
Todd B. Kreutzian Khalid S. A. Seraj Larry G. Anderson Donald C. Zapien 《Electroanalysis》2007,19(23):2479-2482
In this work, long optical path length thin‐layer electrochemical cell was constructed using indium‐tin oxide on glass as the electrode material. Iron release from ferritin adsorbed on the electrode was induced by applying a negative potential sweep in the presence of 1,10‐phenanthroline. The usefulness of spectroelectrochemistry as a means of determining the quantity of iron released from an adsorbed layer of ferritin is demonstrated. 相似文献
1000.
This paper describes a copper selective optical chemical sensor based on static quenching of the fluorescence of 2-(2′-hydroxyphenyl)benzoxazole entrapped in a poly(vinyl chloride) (PVC) membrane. The effect of the composition of the sensing membrane was studied, and experimental conditions were optimized. The sensors exhibit stable response over the concentration range from 4.0 × 10−8 M to 5.0 × 10−5 M Cu2+ at pH 4.0-6.5, and a high selectivity. The response time for Cu2+ with concentration ≤5 × 10−6 M is less than 7 min. The optode can be regenerated using 0.1 M HCl and acetate buffer solution. The sensor has been used for direct measurement of copper content in river water samples with a relative error less than 4% with reference to that obtained by atomic absorption spectrometry. 相似文献