摘要:

Benzene-induced shifts (BIS) in the1H NMR spectra of nine chromeno-compounds have been studied. It provides a simple non-destructive technique for distinguishing linear isomers of chromenoflavones from there angular counterpart. BIS also assists in the assignment of chromene proton signals in chromeno-compounds.

ISSN:0038-7010    

DOI:10.1080/00387019008054032

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The interaction of amphiflavins in organic solvents and a binary (ethanol/water) solvent has been studied. The absorption spectra, steady state and phase sensitive fluorescence spectra, lifetimes, anisotropy and quantum yield of fluorescence have been measured. In a binary solvent the interaction between the amphiflavin molecules and the microenvironment of different polarity leads to the selforganization of amphiflavins. As a result organized structures of amphiflavin molecules appear.

ISSN:0038-7010    

DOI:10.1080/00387019008054033

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The 60 MHz1H NMR spectra of 2-methyl-3-(2′-hydroxymethylphenyl)-4(3H)-quinazolinone,1, a major metabolite of methaqualone, have been studied at 28° in CDCl3solution with the achiral reagent tris (6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium (III),2, and the chiral reagent tris [3-(heptafluoropropylhydroxy-methylene)-d-camphorato]europium (III),3, Lanthanide induced shifts, Δλ, are consistent with major LSR binding at the hydroxyl, and the diastereotopic hydrogens of the CH2are clearly anisochronous. Substantial Δλ values and spectral simplification are achieved with2or3. Significant enantiomeric shift differences, ΔΔλ, are observed with3that should provide direct optical purity determinations of1. Results are discused in terms of LSR binding sites and hindered rotations about selected bonds in1.

ISSN:0038-7010    

DOI:10.1080/00387019008054034

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

An improved method for direct determination of optical purity of the novel benzodiazepine analog, ketazolam,1, is reported. Adding the chiral lanthanide NMR shift reagent, tris[3-(heptafluoropropylhydroxymethylene)-d-camphorato] ytterbium (III), Yb(HFC)3, to racemic ketazolam in CDCl3solution allows observation of enantiomeric shift differences for six of the ketazolam proton resonances. The C(2) methyl1H signal is especially appropriate for the determination of optical purity since the C(2) methyl resonance of each enantiomer are clearly resolved (for accurate peak intensity determination) at 200 MHz. For racemic1, using a molarratio of Yb(HFC)3:1of 0.20, the valley height between the peaks of the two enantiomers′ CCH3signals was only 4.8% of the average peak heights. Detection of as little as 2–3% of a minor enantiomer should be possible. Some aspects of the hindered phenyl rotation in1and the LSR-induced broadening of certain NMR signals are also discussed.

ISSN:0038-7010    

DOI:10.1080/00387019008054035

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The i.r. spectra of indazole have been measured from 4000 to 180 cm−1; polarized spectra of single crystals have been also obtained. The Raman spectra of polycrystalline samples and solutions have been recorded and the polarization of many lines has been determined. Most vibrations have been assigned on the basis of the i.r. dichroism, Raman spectra and correlative arguments.

ISSN:0038-7010    

DOI:10.1080/00387019008054036

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Aspectrophotometric method is presented for the determination of Ascorbic Acid and Analgin in prescence of each other using a first dervative spectrophotometry. By measuring the absolute value of the first-order contribution of both drugs in prescence of each other. The concentration of both drugs can be calculated without interference from each other. The method was proved using synthetic mixtures of Ascorbic Acid and Analgin in prescence of each other.

ISSN:0038-7010    

DOI:10.1080/00387019008054037

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The IR spectra of the title compounds are recorded and an assignment of the normal modes in terms of local symmetry is suggested by comparison with those observed in analogous molecules. A set of force constants calculated for simplified models confirms most of the experimental assignments and reflects the symmetry of the complexes under study. ThefCOof the two different CO groups in the cationic complexes indicated that CO groups cis to the halide ligand should be more selective towards nucleophiles.

ISSN:0038-7010    

DOI:10.1080/00387019008054038

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The twisting of the A-, B-, and D- rings of β-arteether were determined from dihedral angles derived from3JHHcoupling constants and a Karplus-type equation that takes into account heteroatom substitution. The angles obtained by NMR were also compared to the angles obtained by molecular modeling and to those obtained from the methyoxyl analog (artemether) using x-ray crystallography. The NMR results showed that the A-ring was a relatively undistorted chair conformation with the 14-methyl group in an equatorial position. The NMR data indicated that the B-ring was very distorted and the D-ring was twisted outward because of the steric interactions with the ethoxy group. Two-dimensional NOESY data was used to measure selected proton-proton distances for arteether in solution and these distances were also compared to those obtained by molecular modeling and from the x-ray data for artemether. The NOESY data also indicated that the conformation of the A-ring was fairly normal, the B-ring was twisted, and the ethoxy group was in an extended conformation (C11-C12-O-C16=+170°, and C12-O-C16-C17=+169°)

ISSN:0038-7010    

DOI:10.1080/00387019008054039

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A simple spring model for molecular vibrations, which uses Cartesian co-ordinates for both longitudinal and transverse displacements, is applied to non-centrosymmetric linear triatomic molecules. Analytical expressions for the stretching and bending mode frequencies are obtained, which are equivalent to those derived by conventional methods. For most molecules, the effects of the interaction between the outside atoms are shown to be negligible, but for N2O, complex solutions are obtained unless this is included. The validity of the model is demonstrated by the satisfactory agreement between calculated and observed frequencies of isotopic species. For N2O, frequency shifts resulting from isotopic substitution are explained by reference to the calculated eigenvectors.

ISSN:0038-7010    

DOI:10.1080/00387019008054040

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The IR spectra of nitrobenzene-d0and -d5were recorded in gas and liquid phases at 25°C and in amorphous solid phase at -170°C. The appearance of new bands and intensity changes going from liquid to solid phase spectrum, are interpreted in terms of molecular symmetry modifications. A normal coordinates analysis was performed and the potential energy distribution agrees well with previous assigments.

ISSN:0038-7010    

DOI:10.1080/00387019008054041

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor