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1.
The cesium enolate of 6-phenyl-alpha-tetralone (CsPAT) has a lambda(max) in THF at about 387 nm, but the variation with concentration is too small for application of singular value decomposition. Proton-transfer studies with several indicators show that CsPAT forms monomer-tetramer mixtures with a tetramerization equilibrium constant, K(1,4) = 2.3 x 10(11) M(-3). The pK of the monomer is 23.39 on a scale where fluorene is assigned 22.9 (per hydrogen). For comparison, the lithium enolate, LiPAT, is also a monomer-tetramer with K(1,4) = 4.7 x 10(10) M(-3) and a monomer pK = 14.22. HMPA in large amounts promotes dissociation to monomer with both enolates. Ion-pair S(N)2 initial rates were measured for CsPAT with several alkyl halides and with methyl tosylate and compared with other rates with LiPAT. In all cases, the enolate monomers are much more reactive than the aggregates. Reaction of CsPAT with alkyl halides is generally C-alkylation but HMPA promotes increasing amounts of O-alkylation. A new indicator, 11-methyl-11H-benzo[b]fluorene, has a pK on the cesium scale of 23.39. 相似文献
2.
Dimitris K. Agrafiotis Brian Tansy Andrew Streitwieser 《Journal of computational chemistry》1990,11(9):1101-1110
Two new computational methods for the evaluation and partitioning of projected, planar, and averaged slab electron densities, implemented in the program PRODEN, are presented. The new algorithms for the projection, demarcation, and integration of electron densities are described and evaluated in terms of speed and numerical accuracy. Integrated Projected Populations are analyzed and some of the advantages and limitations of the methods are discussed. 相似文献
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The basicity of 1,3-di-tert-butylimidazol-2-ylidene (1) was measured in THF against three hydrocarbon indicators. Both ion pairs and free ions were found and the corresponding equilibrium constants were measured. Homoconjugation was not found in either THF or DMSO. The carbene is effectively more basic in DMSO by several pK units, probably because of hydrogen bonding of 1-H(+) to DMSO. Model ab initio computations are consistent with these results. 相似文献
5.
Ab initio calculations were used to determine the equilibrium geometries and rotational barriers of the pentadienyl cation, anion, and metalated pentadienes. Pentadienyllithium and pentadienylsodium are most stable in a U-shaped structure. This geometry is a higher energy local minimum for the pentadienyl anion and is not a stationary point for the pentadienyl cation. The atomic and group charges were analyzed by natural population analysis and were determined for each of the conformations studied. 相似文献
6.
Studies with two lithium enolates show that aggregation varies from comparable to lower in dimethoxyethane (DME) compared to tetrahydrofuran (THF) but that aggregation is much higher in methyl tert-butyl ether (MTBE). Alkylation reactions, which occur dominantly with the enolate monomers, are exceptionally slow in MTBE, but even acylation reactions that can occur with aggregates are orders of magnitude slower in MTBE. These reactions apparently require additional solvation of the lithium cation, and MTBE is ineffective at such solvation. 相似文献
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8.
Streitwieser A Keevil TA Taylor DR Dart EC 《Journal of the American Chemical Society》2005,127(25):9290-9297
Kinetic acidities are reported for methane, ethane, propane, cyclopropane, isobutane, neopentane, tetramethylbutane, norbornane, nortricyclene, and adamantane by tritiodeprotonation or deuteriodeprotonation in cyclohexylamine catalyzed by cesium cyclohexylamide. 相似文献
9.
Proton affinities are calculated at all reactive positions for the normal benzenoid hydrocarbons, benzene, naphthalene, phenanthrene
and anthracene, a strained benzenoid hydrocarbon, biphenylene, and a nonalternant hydrocarbon, fluoranthene, and the results
are compared to experimental protodetritiation rates. Methods used include PM3 and Hartree-Fock calculations at the STO-3G,
3-21G*, 6-31G* and MP2//6-31G* levels. Generally good agreement is found between theory and experiment with 6-31G* giving
the best correlations.
Received: 11 June 1998 / Accepted: 3 September 1998 / Published online: 23 February 1999 相似文献
10.