摘要:

AbstractThe1H and13C NMR spectra of methylenecyclopropane, both in the isotropic phase and in the Merck IV nematic phase, were analysed. The relative signs of the13CH scalar coupling constants were determined. The complete geometry deduced from this study was compared with that from a microwave study, and the discrepancies are discusse

ISSN:0749-1581    

DOI:10.1002/mrc.1260280702

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe major protonation sites of six cardiotonic isomeric 2‐aryl‐n‐methoxy‐1H‐imidazo[4,5‐b]‐ and ‐[4,5‐c]‐pyridines (n = 4–7) were determined by1H and13C NMR methods. All the 1H‐imidazo[4,5‐c]pyridines and the 7‐methoxy derivative of sulmazole were found to protonate at the pyridyl nitrogen. Protonation occurred at the imidazo nitrogen, however, for the 5‐ and 6‐m

ISSN:0749-1581    

DOI:10.1002/mrc.1260280703

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe determination of radical ions is crucial in mechanistic studies of reactions in which single electron transfer is suspected. A13C NMR method based on the interaction of radical anions with tetrahydrofuran (THF) molecules is presented; measurements of the broadening of the THF α‐carbon signal allow determination of the substrate concentration in the range 0.2–1.2M. The spectacular effect observed on addition of small amounts of benzene greatly improved the method. In addition, studies of the spin‐lattice,T1, and of the transverse nuclear,T2, relaxation times and of the effects of added co‐solvents allow the proposal of the bonding situation and of the degree of coordination in the radical anion‐cation‐THF molecu

ISSN:0749-1581    

DOI:10.1002/mrc.1260280704

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe introduction of a substituent in the 3‐position of the pyrrole ring inN‐vinyl‐2‐arylpyrroles and ‐2‐heteroarylpyrroles results in an increase in the dihedral angles between the planes of the pyrrole ring and the aryl (or heteroaryl) residue, and a decrease in the dihedral angle between the planes of the pyrrole ring and the vinyl group. Introduction of the substituent in the 5‐position of the pyrrole ring has the opposite effect on these angles. ForN‐vinyl‐2‐(2′‐furyl)pyrrole, some spectral data suggest the formation of a CH…O hydrogen bond between the α‐hydrogen atom of the vinyl group and the oxygen atom of the furyl ring. This is in accord with the results of

ISSN:0749-1581    

DOI:10.1002/mrc.1260280705

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe conformation of the hormone bradykinin (Arg–Pro–Pro–Gly–Phe–Ser–Pro–Phe–Arg) in DMSO‐d6was investigated using proton NMR spectroscopy at 500 MHz. Complete resonance assignments were made using 2D COSY and NOESY techniques. The chemical shifts, magnitudes of the3JNH‐CαHcouplings, temperature coefficient data on backbone NH protons and intramolecular NOEs were used to obtain information on the conformation. The nonapeptide assumes a rigid structure in DMSO‐d6. Based on the experimental results, a model is proposed using computer‐

ISSN:0749-1581    

DOI:10.1002/mrc.1260280706

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractRadicals produced in aqueous solution by gamma irradiation of the five first glucose oligomers were trapped using 2‐methyl‐2‐nitrosopropane (MNP) and separated by high‐performance liquid chromatography. The electron spin resonance (ESR) spectra were analysed on a microcomputer with a general interactive simulation program (VOYONS). The ESR coupling constants of five radical adducts, which were found in all the oligomers, are reported. A comparison with the coupling constants previously obtained from α‐D‐glucopyranosyl,‐0‐methyl‐α‐D‐glucopyranose, O‐α‐D‐glucopyranosyl‐(1 →4)‐α‐D‐glucopyranose or polyols, irradiated in the liquid phase or in the powder state, provides new information on the chemical structures of the radicals radioinduced in glucose oligomers. As the powder ESR spectra and the main radiolytic products from the gamma‐irradiated oligomers have been found to be comparable to those from irradiated starches, this work is the first step in the elucid

ISSN:0749-1581    

DOI:10.1002/mrc.1260280707

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe13C and15N NMR spectra of someortho‐, meta‐andpara‐substituted methanesulphonanilides were recorded. Correlations of the13C chemical shifts with the appropriate substituent chemical shifts (SCS) for monosubstituted benzenes were excellent and showed enhancement of the substituent effects at C‐1 (parato the substituent). The C‐1 chemical shifts were also examined by means of the dual substituent parameter (DSP) and DSP‐nonlinear resonance equations. The results indicate that the —NHSO2Me moiety is a weak electron donor. The15N chemical shifts of thepara‐substituted compounds were analysed by means of DSP equations and the results compared with those of related compounds.Ortho‐substituted compounds indicate the high sensitivity of15N chemical shifts towards steric compression.T1and nuclear Overhauser enhancement data for the protonated carbons of methyl‐substituted

ISSN:0749-1581    

DOI:10.1002/mrc.1260280708

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe enantiomeric purities of disubstituted β‐lactams were determined by1H and13C NMR spectroscopy using tris[3‐(trifluoromethylhydroxymethylene)‐d‐camphorato]europium(III), Eu(tfc)3, as a chiral shift reagent. Using a [Eu(tfc)3]/[lactam]ratio of 0.5, most of the resonances were split into signal pairs due to the respective enantiomers. The method gives quantitative enantiomeric compositions.13C NMR spectroscopy is more advantageous than1H NMR, which is of limited use owing, for example, to the significant line broadening observed in the1H spectra at [Eu(tfc)3]/[lactam]>0.8. Assignments of the proton and carbon signals were obtained for the two enantiomers of the complexed

ISSN:0749-1581    

DOI:10.1002/mrc.1260280709

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe contributions to the13C NMR spin–lattice relaxation rates of both protonated and non‐protonated carbons of a range of carbocations in superacids were determined from the analysis ofT1values measured over a range of temperatures and at different field strengths. From the data for 1‐adamantyl, 2‐methyl‐2‐norbornyl, 3‐methyl‐3‐nortricyclyl, 2‐phenyl‐2‐norbornyl, cumyl (1‐methyl‐1‐phenylethyl) and methylphenylcyclopropylcarbinyl (1‐cyclopropyl‐1‐phenylethyl) cations, dipole–dipole interactions (both intra‐ and inter‐molecular) were found to be entirely responsible for the relaxation of protonated carbons. However, for the cationic carbons, chemical shift anisotropy contributes significantly to their relaxation at low field strengths (2.3 T) and predominantly at high field strengths (5.8 T). The shielding anisotropies (Δσ) of the cationic carbons were determined as 410–540 ppm, which are amon

ISSN:0749-1581    

DOI:10.1002/mrc.1260280710

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe conformational analysis and the assignment of relative configurations [(RR,SS) and (RS,SR)] to the dia‐stereomeric racemates of two acyclic ketones with two asymmetric carbons, ±‐2,2,7,7‐tetramethyl‐5,6‐diphenyloctan‐3‐one and ±‐5,5‐dimethyl‐1,3,4‐triphenylhexan‐1‐one, have been achieved by analysis of1H‐1H geminal and vicinal coupling constants,13C–1H direct coupling constants and13C chemical shifts. This study allows the establishment of the monoconformational character of the (RR,SS) diastereomers. The application of the empirical equation of Haasnoot

ISSN:0749-1581    

DOI:10.1002/mrc.1260280711

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY