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71.
72.
Freitag MA Pruden TL Moody DR Parker JT Fallet M 《The journal of physical chemistry. A》2007,111(9):1659-1666
Recent studies have mapped the keto-enol tautomerization of malonaldehyde through a general transition structure that leads exclusively to the Z isomer of the enol. However, it will be shown that a competing general transition structure exists that leads to both the E and Z isomers of the enol at the B3LYP/6-31G(d,p) and MP2/6-31G(d,p) levels of theory. Both the RHF- and DFT-based effective fragment potential methods have been used to model solvation effects, and the results are compared with full ab initio calculations. It is found that two bridging water molecules with two discrete DFT-based effective fragment potential solvent waters at the MP2/6-31G(d,p) level of ab initio theory provides the most computationally effective model for solvent effects in this system. It is shown that the relative energies for this QM/MM model differ from the full MP2/6-31G(d,p) energies by an average absolute relative difference of 2.2 kcal mol-1 across the reaction path when the zero-point vibrational energy correction is included. 相似文献
73.
The nature of the 7-substituent has a remarkable effect on the diastereoselectivity of the oxidative rearrangement of indole-2-carboxamides derived from (S)-2-methoxymethylpyrrolidine into chiral 3,3-disubstituted oxindoles. 相似文献
74.
75.
Transition-metal carbene X-H insertion reactions (X=N or O) have been employed in the simple conversion of anilines and phenols into indoles and benzofurans, respectively. Thus copper(II) catalyzed N-H insertion reactions of α-diazo-β-ketoesters with N-methylanilines followed by treatment with acidic ion-exchange resin gives indoles. In a similar manner, dirhodium(II) catalyzed O-H insertion reactions of α-diazo-β-ketoesters with phenols followed by treatment with PPA gives benzofurans. 相似文献
76.
K. J. Moody 《Journal of Radioanalytical and Nuclear Chemistry》2009,279(1):13-24
It has been observed that the intensities of the gamma-rays emitted in the alpha-decay of 245Cm reported in the literature result in calculated concentrations that do not agree with those obtained via other methods.
In this work, a 245Cm sample was chemically isolated from a sample of 249Cf, and the gamma-ray intensities were measured relative to the alpha-particle emission rate of the resulting source; there
is a systematic bias relative to the literature intensities of approximately 8%. In addition, gamma-rays that have never before
been observed in the decay of 245Cm are placed in the level scheme of the decay product, 241Pu. 相似文献
77.
Dustin Moody 《Designs, Codes and Cryptography》2009,52(3):381-390
Bilinear pairings on elliptic curves have been of much interest in cryptography recently. Most of the protocols involving
pairings rely on the hardness of the bilinear Diffie–Hellman problem. In contrast to the discrete log (or Diffie–Hellman)
problem in a finite field, the difficulty of this problem has not yet been much studied. In 2001, Verheul (Advances in Cryptology—EUROCRYPT
2001, LNCS 2045, pp. 195–210, 2001) proved that on a certain class of curves, the discrete log and Diffie–Hellman problems
are unlikely to be provably equivalent to the same problems in a corresponding finite field unless both Diffie–Hellman problems
are easy. In this paper we generalize Verheul’s theorem and discuss the implications on the security of pairing based systems.
相似文献
78.
The syntheses, structural and spectroscopic characterization, fluoride abstraction reactions, and photochemical reactivity of cationic uranyl(VI) phosphine oxide complexes are described. [UO2(OPPh3)4][X]2 (1a, X = OTf; 1b, X = BF4) and [UO2(dppmo)2(OPPh3)][X]2 (2a, X = OTf; 2b, X = BF(4)) are prepared from the corresponding uranyl(VI) chloride precursor and 2 equiv each of AgX and phosphine oxide. The BF4- compounds 1b and 2b are prone to fluoride abstraction reactions in methanol, leading to dinuclear fluoride-bridged uranyl(VI) complexes. Fluoride abstraction of 2b in methanol generates two structural isomers of the fluoride-bridged uranyl(VI) dimer [(UO2(dppmo)2)2(mu-F)][BF4]3 (4), both of which have been structurally characterized. In the major isomer 4C, the four dppmo ligands are all chelating, while in the minor isomer 4B, two of the dppmo ligands bridge adjacent uranyl(VI) centers. Photolysis of 2b in methanol proceeds through 4 to form the uranium(IV) fluoride complex [UO2F2(dppmo)3][BF4]2 (5), involving another fluoride abstraction step. X-ray crystallography shows 5 to be a rare example of a structurally characterized uranium(IV) complex possessing terminal U-F bonds. Complex 5 reverts to 4 in solution upon exposure to air. 相似文献
79.
Ethyl 2-diazo-4,4,4-trifluoro-3-oxobutanoate is a highly versatile intermediate for the synthesis of a wide range of trifluoromethyl heterocycles. With the use of rhodium(II) or copper(II) catalyzed carbene X-H insertion reactions as key steps, a diverse set of trifluoromethyl-oxazoles, -thiazoles, -imidazoles, -1,2,4-triazines, and -pyridines are available from the diazoketoester, either directly in a single step or with just one additional step. 相似文献
80.
E. E. Tereshatov J. M. Gostic R. A. Henderson D. A. Shaughnessy K. J. Moody 《Journal of Radioanalytical and Nuclear Chemistry》2012,293(1):331-337
A new procedure to isolate carrier-free isotopes of Nb and Ta after a 12-MeV proton bombardment of a natural Hf foil has been considered. The cross section of the corresponding natHf(p,x)179Ta reaction has been estimated for the first time as 5.4?±?0.5 mb. The isotopes that were produced were subsequently used for development of procedures for the chemical characterization of element 105 (Db). HF/HNO3 and HNO3/H2O2 media have been chosen and the parameters of the experiments have been optimized. Based on the results obtained in this work, off-line experimental procedures have been proposed for the evaluation of the chemical behavior of Db. 相似文献