摘要:

The 60 MHz1H NMR spectra of the systemic agricultural fungicide, triadimefon,1, have been studied in CDCl3at 28±1° (as the racemic free base) with the added achiral lanthanide shift reagent (LSR), tris(6, 6, 7, 7, 8, 8, 8-heptafluoro-2, 2-dimethyl-3, 5-octanedionato) europium(III), Eu(FOD)3,2, for spectral simplification, and with the chiral LSR, tris [3-(heptafluoropropylhydroxymethylene)-(+) -camphorato)europium(III), Eu(HFC)3,3, to induce enantiomeric shift differences (ΔΔδ) for several nuclei. Significant ΔΔδ values were seen for the two protons of the heterocyclic ring, the OCH methine, and aryl H-2′, 6′ of the chlorophenoxy ring. For each of these nuclei exhibiting ΔΔδ with added 3, the ΔΔδ magnitudes reached maximum values with3:1molar ratios ca. 0. 18–0. 29, and decreased with higher levels of3. To confirm analytical utility of 3 for % e. e. determinations of1, a nonracemic (“spiked”) sample of racemic1, with addedR-(−) triadimefon, was examined with3. At low3:1ratios, both triazole H-3 and H-5, as well as the OCH and aryl H-2′, 6′ protons of (−)-1showed a downfield sense of magnetic nonequivalence with (+) -3. With3:1ratios ca. 0. 8, triazole proton H-3 reversed its sense of magnetic noneguivalence. The H-3 and H-5 signals were useful for % e. e determinations at this higher3:1ratio.

ISSN:0038-7010    

DOI:10.1080/00387019408006638

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The19F-1H heterocorrelated NMR experiments enable the final assignments of structures of six difluorocyclopropane (mono, bis and tris gem) sesquiterpene lactones of helenalin and parthenin series.

ISSN:0038-7010    

DOI:10.1080/00387019408006639

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Glyoxal bis(amidinohydrazone) (GBG) and several analogs thereof are compounds of considerable pharmacological interest, and a variety of HPLC and MECC methods have been developed for their analysis. In these methods, detection is invariably based on the strong UV absorption of the compound. Yet, almost nothing has been known of their UV and VIS spectral properties. In the present paper the UV and VIS Spectroscopy of GBG has been studied in several solvent systems (water, 0. 03 M aqueous sodium acetate buffer, 0. 1 inM aqueous NaOH and dimethylsulfoxide). In the case of solutions in bare water, the shape of the UV spectrum depends drastically on concentration, probably because of changes in the species distribution of GBG as a function of concentration. The spectrum comprises one maximum at ca. 200 nm, and between ca. 250 nin and 400 nm an absorption region with distinctly higher absorbance. In the case of aqueous sodium acetate as well as NaOH solutions, one strong maximum can be detected (at ca. 285–288 nm and 332–337 nm, respectively). In both cases, the maximum occurs at constant wavelength, being independent of concentration. In dimethylsulfoxide, the spectrum of GBG contains an absorption band at distinctly higher wavelengths (λmax354 nm) than in any one of the aqueous solvents studied, indicating that solvent effects are considerable in the UV spectrum of GBG. In no case, distinct absorption could be detected at wavelengths higher than 400 nm. The results indicate that if aqueous media are used as elements in HPLC analyses of bis(amidinohydrazones) or as solvents in direct UV analysis, they must be buffered.

ISSN:0038-7010    

DOI:10.1080/00387019408006640

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A Laplace Transform (LT) method is used to improve the results obtained in a quasi-elastic scattering (QELS) experiment. This is designed to determine the characteristic parameters of a bimodal solution of spherical and rod-like macromolecules. The theoretical study and the experimental simulation are carried out for low light levels and the results show that the LT technique provides a real alternative to the second order correlation function, g(2)(τ), in QELS measurements for these particularly difficult experimental conditions.

ISSN:0038-7010    

DOI:10.1080/00387019408006641

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The Carbon-13 NMR spectra of dihydrocarveol and dihydrocarvyl acetate stereoisomers are characterized. The chemical shifts are assigned taking account the steric and electronic substituent effects, the lanthanide induced shifts and the proton-carbon correlation.

ISSN:0038-7010    

DOI:10.1080/00387019408006642

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The antihyperlipoproteinemic agent, acifran, has been studied as its racemic methyl ester,1, by 60 MHz1H NMR in CDC13solution at 28±1° with the added achiral lanthanide shift reagent (LSR), tris(6, 6, 7, 7, 8, 8, 8-heptaf luoro-2, 2-dimethyl-3, 5-octanedionato-europium(III), Eu (FOD)3,2, for spectral simplification, and with the chiral LSRs, tris[3-(heptafluoropropylhydroxymethylene)-(+)-camphorato]europium(III), Eu(HFC)3,3, and tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorato]europium(III), Eu (FACAM)3,4, for potential determinations of enantiomeric excess. Relative lanthanide-induced shift (LIS) magnitudes with the three LSRs were interpreted as consistent with major lanthanide binding at the 4-oxo carbonyl, but contrasting behavior in observed enantiomeric shift differences (ΔΔδ) with3versus4may suggest different bound complex geometries for3or4with1.

ISSN:0038-7010    

DOI:10.1080/00387019408006643

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Mixed copper aluminium oxide has been studied by XPS. It was shown that the reduction under hydrogen of the precursor oxide leads to the formation of cuprous ions located in the octahedral sites of the spinel matrix γ-A1203and hydridic species stored in the solid. The use of the pre-reduced compound at 300°C before catalysis with H2/CO is necessary to maintain almost intact the spinel phase despite the formation of metallic copper, whereas a strong modification of a surface composition was obseved when the solid is directly treated by H2/CO mixture.

ISSN:0038-7010    

DOI:10.1080/00387019408006644

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0038-7010    

DOI:10.1080/00387019408006645

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor