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11.
Some gauge invariant atomic orbitals-coupled-perturbed Hartree-Fock (GIAO-CPHF) calculations were performed for seven indolizine derivatives and their monoprotonated forms. Chemical shift, molecular geometry, and charge distribution data are reported for each molecule. The calculations support the results of nuclear magnetic resonance (NMR) spectroscopy measurements showing that protonation occurs preferentially at N1. The good agreement between the calculated and observed 13C and 15N chemical shifts show that such calculations can be used for chemical shift assignment purposes. Cation structures and probable sites for electrophilic reaction or second protonation are also discussed. 相似文献
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A variable-temperature (1)H- and (13)C-NMR study revealed a conformational equilibrium for 1,3,3,5,7,7-hexamethyl-1,5-diazacyclooctane (4) having DeltaG() = 8.8 +/- 0.6 kcal/mol at 184 K. This activation barrier connects a major and a minor form of 4. Molecular mechanics calculations on 4 led to the conclusion that the major form is a set of twist-chair-chairs interconverting rapidly via the chair-chair and that the minor form is most likely a set of twist-boat-boats interconverting rapidly via the boat-boat. The proximity of the two nitrogen lone pairs in the major form of 4 made plausible the expectation that 4, as well as a related diamine with apposed nitrogens, 3,7-dimethyl-3,7-diazabicyclo[3.3.1]nonane (3), might bind a Lewis acid, namely BH(3), using both lone pairs simultaneously and equally. This proved not to be the case: for 3 only the bis-BH(3) adduct was found and for 4 the mono-BH(3) adduct utilized only one nitrogen lone pair. The structure of the bis-BH(3) adduct of 4 (12) was determined by X-ray crystallography to be a twist-boat-boat with BH(3)s cis. Molecular mechanics calculations on 12 were consistent with the solid state conformation found. 相似文献
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W. Bocian J. Jaźwiński O. Staszewska J. W. Wiench L. Stefaniak G. A. Webb 《Chemistry of Heterocyclic Compounds》1996,32(11-12):1358-1366
Multinuclear1H,13C,14N,15N, and17O NMR data are presented for some sydnones, isosydnones and isothiosydnones. The type of valence tautomerism shown in (Fig. 1) is not observed for the compounds studied. At high pH compounds2 and12 are found to undergo transformations. The more suitable NMR parameters are reported for establishing the structures of mesoionic compounds containing three heteroatoms in the five-membered conjugated ring. Someab initio GIAO calculations on a model structure of sydnones and related compounds have been performed. 相似文献
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The continuous flow hydroformylation of 1-octene catalysed by Rh/[RMIM][Ph(2)PC(6)H(4)SO(3)](R = 1-propyl, 1-pentyl or 1-octyl) dissolved only in the steady state reaction mixture and using scCO(2) as a transport vector for both substrates and products gives rates up to 160-240 catalyst turnovers h(-1) with low rhodium leaching over a 12 h period at a total pressure of 125-140 bar. 相似文献
19.
Functionalization of the 4(5)methyl group of imidazoles: A novel synthesis of substituted imidazoles
Acyl vinyl phosphonium salts react with amidines to form imidazolyl phosphonium salts. These imidazolyl salts can be readily converted to multifunctional imidazoles with quantitative recovery of triphenyl phosphine. 相似文献
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Webb AG 《Magnetic resonance in chemistry : MRC》2005,43(9):688-696
The increased separation efficiency afforded by reducing the size of the separation column has resulted in 'microseparations' becoming an important component in many chemical and biochemical applications. The coupling of microseparations with NMR detection is an area of increasing interest owing to the high structural information of NMR. In order to couple efficiently with the separation, the NMR detector must be reduced in size to correspond to that of the separation peak. This paper summarizes some of the approaches used in coupling NMR detection with pressure-driven and electrophoretic microseparations, the design of small NMR detectors and applications of this technology. 相似文献