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排序方式: 共有116条查询结果,搜索用时 312 毫秒
1.
Sivaramakrishnan R Tranter RS Brezinsky K 《The journal of physical chemistry. A》2005,109(8):1621-1628
Density functional theory (DFT) has been used along with isodesmic reaction schemes to estimate heats of formation for aromatics and polynuclear aromatic hydrocarbons (PAHs). Calculations have been performed for 42 molecules, 12 of which have uncertain or unknown experimental values, using the B3-LYP functional with the small 6-31G(d) basis set. Heats of formation for the group of test molecules were estimated using both conventional bond separation (BS) isodesmic reactions as well as a new technique of ring conserved (RC) isodesmic reactions which is able to correct systematic errors in B3-LYP calculations. When a ring conserved isodesmic reaction based on delocalization energies is used, the estimated heat of formation is more accurate than that obtained by the bond separation technique. The methodology for creating and using appropriate ring conserved isodesmic reactions is discussed. The present scheme also compares favorably against a recently developed bond centered group additivity scheme that was tested against a large number of PAH molecules. 相似文献
2.
K. P. Sivaramakrishnan C. Samyn Ira John Westerman Daniel Ting-Man Wong C. S. Marvel 《Journal of polymer science. Part A, Polymer chemistry》1975,13(5):1083-1094
1,3-Bis(p-phenoxybenzenesulfonyl)benzene, 4,4′-bis(p-phenoxybenzenesulfonyl)diphenyl ether, and 4,4′-diphenoxydiphenyl sulfone were polymerized with isophthaloyl or terephthaloyl chlorides in Friedel-Crafts type polymerizations. These polymers had [2,2]p-cyclophane units in the backbone, introduced by employing 3,9-bis(p-phenoxybenzoyl) [2.2]p-cyclophane as part of the polyaryl ether component. Thermolysis of the dimethylene bridge of the [2.2]p-cyclophane monomer produced diradicals which combined across polymer chains to provide crosslinks. p-Cyclophane polymers with 1,3-bis-(p-phenoxybenzenesulfonyl)benzene showed potential as high performance, thermally stable laminating resins. 相似文献
3.
Parthiban A. Lingam K. Arun Prasath Mangalaraj S. Muthukrishnan P. Surendiran M. 《Journal of Cluster Science》2021,32(5):1401-1409
Journal of Cluster Science - Single crystal electron paramagnetic resonance (EPR), powder X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) and UV–Visible (UV–Vis)... 相似文献
4.
5.
A mild, efficient, and high-yielding method for the synthesis of 2-aryl-2,3-dihydroquinolin-4(1H)-ones from their corresponding 2-amino chalcones using silica chloride (SiO2Cl) under solvent-free conditions is described. A series of 2-aryl-2,3-dihydroquinolin-4(1H)-ones containing both electron-donating and electron-withdrawing substituents were synthesized. 相似文献
6.
Two uncoupled two-level atoms cannot be jointly excited by classical light under general circumstances, due to destructive interference of excitation pathways in two-photon absorption. However, with temporally entangled light, two-atom excitation is shown possible. Photons arising from three-level cascade decay are intrinsically ordered in time of emission. This field correlation induces a joint resonance in the two-atom excitation probability via suppression of one of the time-ordered excitation pathways. The relative gain in two-photon absorption increases with the time-frequency entanglement. 相似文献
7.
A variety of privileged bis-spirochromanones were synthesized for the first time from 4,6-diacetyl resorcinol in one-pot by carrying out the Kabbe condensation in room temperature ionic liquid [bbim]Br. 相似文献
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9.
Yujie Tao Ahren W. Jasper Yuri Georgievskii Stephen J. Klippenstein Raghu Sivaramakrishnan 《Proceedings of the Combustion Institute》2021,38(1):515-522
Recent theoretical studies have shown that termolecular chemistry can be facilitated through reactions of flame radicals (H, O, and OH) or O2 with highly-energized collision complexes (either radical or stable species) formed in exothermic reactions. In this work, radical-radical recombination reaction induced termolecular chemistry and its impact on combustion modeling was studied. Two recombination reactions, H + CH3 + M → CH4 + M and H + OH + M → H2O + M, were analyzed using ab-initio master equation analyses guided by quasiclassical trajectory results. The dynamics results and the master equation calculations indicate that CH4? and H2O? (formed in the two radical-radical reactions outlined above) react rapidly with flame radicals and O2 at rates that are competitive with collisional cooling. The addition of these processes into conventional combustion modeling requires two modifications: the inclusion of the new nonthermal termolecular reaction rates and the simultaneous reduction of the competing recombination reaction rates. The former is described with newly derived Arrhenius expressions based on quasiclassical trajectories, and the latter is achieved by perturbing the recombination reaction rate during the simulation. Kinetic modeling was used to gauge the impact of including this nonthermal chemistry for H2/CH4-air laminar flames speeds. Inclusion of this nonthermal chemistry has a noticeable impact on simulated flame speeds. The procedure developed here can be utilized to properly quantify the effects of such nonthermal reactions in macroscopic kinetic models. 相似文献
10.
Vyas S Muthukrishnan S Kubicki J McCulla RD Burdzinski G Sliwa M Platz MS Hadad CM 《Journal of the American Chemical Society》2010,132(47):16796-16804
The photochemistry of diphenylphosphoryl azide was studied by femtosecond transient absorption spectroscopy, by chemical analysis of light-induced reaction products, and by RI-CC2/TZVP and TD-B3LYP/TZVP computational methods. Theoretical methods predicted two possible mechanisms for singlet diphenylphosphorylnitrene formation from the photoexcited phosphoryl azide. (i) Energy transfer from the (π,π*) singlet excited state, localized on a phenyl ring, to the azide moiety, thereby leading to the formation of the singlet excited azide, which subsequently loses molecular nitrogen to form the singlet diphenylphosphorylnitrene. (ii) Direct irradiation of the azide moiety to form an excited singlet state of the azide, which in turn loses molecular nitrogen to form the singlet diphenylphosphorylnitrene. Two transient species were observed upon ultrafast photolysis (260 nm) of diphenylphosphoryl azide. The first transient absorption, centered at 430 nm (lifetime (τ) ~ 28 ps), was assigned to a (π,π*) singlet S(1) excited state localized on a phenyl ring, and the second transient observed at 525 nm (τ ~ 480 ps) was assigned to singlet diphenylphosphorylnitrene. Experimental and computational results obtained from the study of diphenyl phosphoramidate, along with the results obtained with diphenylphosphoryl azide, supported the mechanism of energy transfer from the singlet excited phenyl ring to the azide moiety, followed by nitrogen extrusion to form the singlet phosphorylnitrene. Ultrafast time-resolved studies performed on diphenylphosphoryl azide with the singlet nitrene quencher, tris(trimethylsilyl)silane, confirmed the spectroscopic assignment of singlet diphenylphosphorylnitrene to the 525 nm absorption band. 相似文献