摘要:

Ambiguities in the13C NMR chemical shift assignments of 1-nitropyrene were resolved using direct and long-range two-dimensional heteronuclear chemical shift correlation experiments. The latter was modified with a bilinear rotational decoupling (BIRD) pulse sequence, which enabled detection of all three-bond long-range correlations.

ISSN:0038-7010    

DOI:10.1080/00387019108018119

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Vibrational spectra have been obtained for quite a few monobromo1–15and dibromoalkanes16–32, most of which were shown to exhibit rotational isomerism. However, very few tribromo23,33,34and tetrabromoalkanes28,35,36have been studied. Therefore, IR spectra have been obtained for 1,2,4,5-tetrabromopentane (TBP), and molecular mechanics calculations have been made for the six spectroscopically distinguishable conformers of this molecule that have all five carbons coplanar, in order to learn something about the molecule's conformational behavior. The calculations were made with the MM2 program written by Allinger and Yuh and converted by Petillo to run on a microcomputer.37The six conformers of TBP can be represented by the following skeletal formulas, where a + indicates a bromine on one side of the plane of carbons and a − indicates a bromine on the other side of that plane:

ISSN:0038-7010    

DOI:10.1080/00387019108018120

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A simple spring model for molecular vibrations is applied to non-linear triatomic ABC-type molecules with Cspoint group. The development is in terms of Cartesian co-ordinates, which offers certain advantages for extensions to lattice dynamics calculations. Analytical expressions for the three normal mode frequencies are derived in terms of two stretching and one bending force constants. The model is applied to a number of ABC-type molecules and to asymmetric isotopic species of AB2-type non-linear molecules. The validity of the model is demonstrated by the satisfactory agreement between calculated and observed frequencies of isotopic species. Examination of the calculated eigenvectors shows that mixing between the A-B and B-C stretches and ABC bend is appreciable. For DOC1 a new value of the bending frequency is suggested.

ISSN:0038-7010    

DOI:10.1080/00387019108018121

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We have studied the behaviour of the brain pentapeptide leucineenkephalin on phosphoric acid spiked glycerol matrices under FAB-PI conditions. Ion series of the general formula [mM+nH3PO4+H]+, [mM+H+62]+and [mM+H3PO4+H+62]+were observed. Experiments using labelled glycerol, methionine-enkephalin and various spiking agents were performed along with B/E linked scans in order to investigate the nature of the latter two series of ions; they led to the conclusion that the +62 ions originate from the slow decomposition of H3PO4-peptide aggregates.

ISSN:0038-7010    

DOI:10.1080/00387019108018122

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

1HNMR spectra of the title compounds have been measured as the function of the mole fraction of benzene in the mixture solvent of benzene and CC14. As the mole fraction of benzene increases, the chemical shifts (δ) of two methyl groups in a molecule and of benzene gradually move upfield. The upfield shifts of different methyl groups in a molecule are not equal to one another. The Δδ of β-CH3is larger than that of α-CH3. Thus, the two lines appear to coalesce at a certain concentration and to cross over with the increment of the proportion of benzene. All of the chemical shifts can be related with a linear equation (δ=A+BX). Where, X is the mole fraction of benzene in the mixture solvent. The correlation coefficients R are approximately equal to 1.

ISSN:0038-7010    

DOI:10.1080/00387019108018123

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In the magnetic resonance imaging (MRI) technique the local tissue characterization is accomplished by measurements of the standard NMR parameters.

ISSN:0038-7010    

DOI:10.1080/00387019108018124

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The i. r. spectra of benzimidazol-2-thione 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:10.1080/00387019108018125

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In this work the reaction between oxamniquine as n donor and iodine as sigma acceptor was studied,. Different parameters involved in the reaction were investigated such as choice of solvent, iodine concentration, time, light and temperature. Also the stoichiometry of the reaction was determined. Thus, a spectrophotometric procedure has been developed for the determination of oxamniquine by reaction with iodine and measurement of absorbance of the formed charge transfer complex at λ 291 and λ 360 nm. Molar absorptivities, A 1%, 1 cm and the regression equations were computed. The proposed procedure was applied for the determination of oxamniquine in its dosage forms. Accurate and precise results were obtained when compared to the manufacturer's procedure.

ISSN:0038-7010    

DOI:10.1080/00387019108018126

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The unsubstituted phenyl ring in ketazolam, a 1,4-benzodiazepine derivative, has a two-fold rotational barrier about the aryl to tert-alkyl bond connecting this phenyl group to the rest of the molecule. At 50.3 MHz, all twenty of the13C resonances of ketazolam are resolved below -40°C, including two distinct resonances for theorthocarbons and two for themetacarbons. Twelve of the twenty13C nuclei resonate between 138 and 125 ppm, necessitating assignment via a combination of one-bond and long-range heteronuclear shift correlation experiments.

ISSN:0038-7010    

DOI:10.1080/00387019108018127

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Electronic and resonance Raman spectra are reported for the [Fe(Hdmg)2(clpz)]npolymer (clpz = 2-chloropyrazine, Hdmg = dimethylglyoximato anion). Excitation at the absorption bands in the visible region led to a selective enhancement of vibrational modes of the Hdmg and clpz ligands, allowing the characterization of the metal-to-macrocycle and metal-to-axial ligand charge-transfer transitions.

ISSN:0038-7010    

DOI:10.1080/00387019108018128

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor