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91.
92.
G.A. Crowder 《Journal of fluorine chemistry》1973,3(2):125-131
Normal coordinate calculations have been carried out for CF3CH2Cl using a 30-parameter valence force field. The resulting force constants for the CF3 group have been transferred to CF3CH2F, CF3CH2Br and CF3CH2I with excellent results. Previous vibrational assignments have been revised, the calculations showing that several of the normal modes are highly mixed. 相似文献
93.
Infrared spectra were obtained for n-butyl, n-pentyl, and n-hexyl fluorides in the liquid and solid states, and liquid-state Raman spectra were obtained for the first two of these. Normal coordinate calculations were carried out and twenty force constants of the C-CH2F group were refined to provide the best fit for the 114 assigned frequencies of trans-n-propyl, gauche-n-propyl, TT-n-butyl, and TG-n-butyl fluorides. The resulting force constants were used to calculate the frequencies of the GT- and GG conformations of n-butyl fluoride and the two conformations for each of n-pentyl and n-hexyl fluoride that have coplanar carbon chains. The presence of all four conformers of n-butyl fluoride in the liquid state is indicated, but only the TG-conformer is present in the solid. The existence of the two conformations of n-pentyl and n-hexyl fluorides for which calculations were made is supported by comparison of the observed and calculated frequencies. Additional conformations seem to be present. The simplest solid-state spectrum is due only to the conformer that has a coplanar chain of carbons and the fluorine atom in the gauche position. Previous tentative conclusions about the relation between C-F stretching frequency and configuration have been revised. 相似文献
94.
Infrared spectra have been redetermined for fluoroacetone in the vapor, liquid, and solid states, and Raman spectra have been obtained for the liquid. There are two rotational isomers present in the liquid, but only the more polar form is present in the crystalline solid and only the less polar form is present in the vapor. Vibrational assignments were made for the two rotamers with the aid of normal coordinate calculations that utilized a twenty-five parameter valence force field. 相似文献
95.
Many organic compounds exist as equilibrium mixtures of two or more molecular conformations, and vibrational spectroscopy can be used to obtain information about the structure of those conformations. Normal coordinate calculations are often an aid to those conformational studies and to making vibrational assignments for the different conformers. However, sometimes those calculations are partially inconclusive, and a few results are briefly discussed in which both conclusive and inconclusive results were obtained from calculations. Calculations are then applied to some 1,2-dichloro- and 1,2-dibromo-alkanes. Previous calculations on 1,2-dichloropropane and 1,2-dichlorobutane are revised, and calculations are reported for 1,2-dibromopropane, 1,2-dibromopropane-d6, and 1,2-dibromobutane. Spectra are given for the last two of these compounds. A modified valence force field was determined for each family of 1,2-dihaloalkane that should be transferable to other members of the family. 相似文献
96.
G.A. Crowder 《Journal of fluorine chemistry》1977,10(3):241-246
Normal coordinate calculations were made for CF3CH3, using a twenty-two parameter modified valence force field. Thirteen force constants were constrained to the CF3CH2X values and nine were adjusted to fit the twelve frequencies, resulting in an average error of 2.3 cm/t-1. The CF3 group force constants should be useful in calculations for other compounds containing this group. 相似文献
97.
Droplet aggregation is an important cause of instability in emulsions because it may, on one hand, lead to an increased creaming rate, resulting in fast separation of a concentrated emulsion phase (creamed layer). On the other hand, it may also lead to the formation of a stabilizing, droplet-based network. Early detection of instability is often difficult due to the high turbidity and viscosity of more concentrated food emulsions. The applicability of diffusing-wave spectroscopy (DWS) for monitoring droplet aggregation and creaming was studied using a model system consisting of a protein-stabilized emulsion, to which a soluble polymer ("thickener") was added. This addition leads to an increased solvent viscosity and may induce droplet aggregation. In addition, the redistribution process of emulsion droplets in aggregating concentrated emulsions was directly observed by confocal scanning laser microscopy (CSLM). By DWS the decrease of the droplet mobility caused by the viscosity increase of the continuous phase could be separated from the effect of droplet aggregation. Moreover, a distinction could be made between aggregation, leading to increased creaming rates and that leading to the formation of a stabilizing droplet network. The potential of DWS for in situ measurement of the stability of concentrated emulsions is discussed. Copyright 2000 Academic Press. 相似文献
98.
Anne L Carenbauer James D Garrity Gopal Periyannan Robert B Yates Michael W Crowder 《BMC biochemistry》2002,3(1):4-13
Background
The metallo-β-lactamases are Zn(II)-containing enzymes that hydrolyze the β-lactam bond in penicillins, cephalosporins, and carbapenems and are involved in bacterial antibiotic resistance. There are at least 20 distinct organisms that produce a metallo-β-lactamase, and these enzymes have been extensively studied using X-ray crystallographic, computational, kinetic, and inhibition studies; however, much is still unknown about how substrates bind and the catalytic mechanism. In an effort to probe substrate binding to metallo-β-lactamase L1 from Stenotrophomonas maltophilia, nine site-directed mutants of L1 were prepared and characterized using metal analyses, CD spectroscopy, and pre-steady state and steady state kinetics. 相似文献99.
Infrared and Raman spectra are obtained for 1-chloro-2-methylpropane and 1-chloro-2,2-dimethylpropane. The former compound exists as a mixture of PC and PH' conformers in the liquid and unannealed solid states, but only the PC conformer is present in the crystalline solid. Vibrational assignments are made for both conformers of 1-chloro-2-methylpropane and for 1-chloro-2,2-dimethylpropane with the aid of normal coordinate calculations. 相似文献
100.
IR and Raman spectra have been obtained for 1,1-dichlorobutane and interpreted with the aid of normal coordinate calculations. It is concluded that this compound exists in three conformations in the liquid and glassy solid states but crystallizes only in the conformer that has all four carbons coplanar and both chlorines out of that plane (Cs symmetry). 相似文献