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71.
72.
A series of geometry, frequency, and energy calculations of chloroaquazinc(II) complexes were carried out at up to the MP2/6-31+G* level. A thorough examination of all species up to and including hexacoordinate species, and with up to six chlorides, was carried out. The structures of the complexes are compared with experimental data where available. The solution chemistry of zinc(II) in the presence of chloride is discussed, and Raman spectra of zinc perchlorate with increasing amount of chloride are presented. 相似文献
73.
J. I. Degraw J. C. Christensen V. H. Brown M. J. Cory 《Journal of heterocyclic chemistry》1974,11(3):363-367
The svnthesis of 1-(2′-bromo-4′-methoxy-5-hydroxybenzyl)-6-keto-Δ4a-5-decahydroisoquinoline (IX) is described. Efforts to cyclize this intermediate or its N-acyl derivatives in acidic media to morphinan products were unsuccessful. The presence of the para-bromine blocking group apparently exerts a deactivating influence on the phenolic ring. 1-(3′,5′-Dihydroxy-4′-methoxybenzyl)-6-methoxy-1,2,3,4,5,8-hexahydroisoquinoline (XVIII) was readily cyclized to 2-hydroxydihydronorthebainone. However, attempts to remove the 2-hydroxy group and subsequent conversion to dihydronorcodeine were unrewarding. 相似文献
74.
A simple, customizable connectivity scheme is rigorously defined in which pairs of atoms are classified into three categories. The tools of graph theory are used to analyze the molecular graph and to efficiently find rings and ring assemblies through a combination of pruning and homeomorphic reduction. The definition of natural internal coordinates is extended in a nonredundant fashion for the various cases of weakly interacting components and for fused ring systems. The ring system coordinates were tested and found to be superior to Z-matrix coordinates. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 504–511, 1998 相似文献
75.
76.
The conductor-like screening model (COSMO) of solvation has been implemented in the Amsterdam density functional program
with maximum flexibility in mind. Four cavity definitions have been incorporated. Several iterative schemes have been tested
for solving the COSMO equations. The biconjugate gradient method proves to be both robust and memory-conserving. The interaction
between the surface charges and the electron density may be calculated by integrating over either the fitted or exact density,
or by calculating the molecular potential. A disk-smearing algorithm is applied in the former case to avoid singularities.
Several self-consistent field/COSMO coupling schemes were examined in an attempt to reduce computational effort. A gradient-preserving
algorithm for removing outlying charge has been implemented. Preliminary optimized radii are given. Applications to the benzene
oxide-oxepin valence tautomerization and to glycine conformation are presented.
Received: 13 November 1998 / Accepted: 16 December 1998 / Published online: 16 March 1999 相似文献
77.
C H Tseng G P Wong V R Pomeroy R W Mair D P Hinton D Hoffmann R E Stoner F W Hersman D G Cory R L Walsworth 《Physical review letters》1998,81(17):3785-3788
NMR images of laser polarized 3He gas were obtained at 21 G using a simple, homebuilt instrument. At such low fields magnetic resonance imaging (MRI) of thermally polarized samples (e.g., water) is not practical. Low-field noble gas MRI has novel scientific, engineering, and medical applications. Examples include portable systems for diagnosis of lung disease, as well as imaging of voids in porous media and within metallic systems. 相似文献
78.
79.
T. Pavlin R. Wang R. McGorty M. S. Rosen D. G. Cory D. Candela R. W. Mair R. L. Walsworth 《Applied magnetic resonance》2007,32(1-2):93-112
We present a novel nuclear magnetic resonance (NMR) technique that provides a noninvasive, direct measurement of gas exchange
in a three-dimensional gas-fluidized bed of solid particles. The NMR spectrum of hyperpolarized 129Xe gas in an Al2O3 particle bed displays three resolved peaks corresponding to xenon in bubbles, the interstitial spaces (emulsion), and adsorbed
on particles. Modified NMR exchange and saturation recovery sequences, together with data analysis based on an exchange-coupled
set of Bloch equations, yield gas exchange rate constants between the emulsion and adsorbed phases, and between the bubble
and emulsion phases. The results are in approximate agreement with previously unverified predictions from well-known models
of fluidized bed behavior. Incorporation of NMR imaging methodologies would straightforwardly allow similar measurements on
a spatially resolved basis.
Authors' address: Ross W. Mair, Harvard Smithsonian Center for Astrophysics, MS 59, 60 Garden Street, Cambridge, MA 02138,
USA 相似文献
80.
Beshara CS Hall A Jenkins RL Jones TC Parry RT Thomas SP Tomkinson NC 《Chemical communications (Cambridge, England)》2005,(11):1478-1480
A mild, efficient and general method for the chemospecific alpha-oxygenation of aldehydes is described. Treatment of a series of aldehydes with N-tert-butyl-O-benzoyl hydroxylamine hydrochloride gives the corresponding alpha-oxygenated carbonyl via a proposed pericyclic rearrangement process. 相似文献