摘要:

AbstractPotential energy calculations (MM2), low‐temperature1H and13C NMR spectra and1H–1H COSY spectra are reported for four octane derivatives, the central portions of which constitute tetrasubstituted succinates. The existence of several conformers differing in stereochemistry in this central moiety is predicted by calculations and observed in low‐temperature NMR. The periphery of each molecule is in an extended configuration, as shown by the existence of long‐range (W‐plan) couplings involving the meth

ISSN:0749-1581    

DOI:10.1002/mrc.1260290202

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe application of two‐dimensional phase‐sensitive COSY, ROESY and13C–1H shift correlation spectroscopy in the structural elucidation and stereochemical assignment of the steroidal alkaloids 15‐(2‐methylbutyryl)germine, 3‐(2‐hydroxy‐2‐methylbutyryl)‐15‐(2‐methylbutyryl)germine and 16‐(2‐methylbutyryl)germine is reported. It is shown that two‐dimensional13C–1H heteronuclear long‐range correlation spectroscopy is an invaluable method for the stereochemical assignment of proton resonances which overlap in1H NMR an

ISSN:0749-1581    

DOI:10.1002/mrc.1260290203

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe1H NMR spectrum of the Pt(0) complex Pt(trans‐MeO2CCHCHCO2Me)2[P(cyclohexyl)3] was measured and the structures of the two isomeric forms, which differ with respect to olefin coordination, were assigned. The structural study made use of a complete analysis of the 11 non‐equivalent protons of the P(cyclohexyl)3in one isomer, and this was accomplished via DQF‐COSY and13C,1H inverse heteronuclear correlation

ISSN:0749-1581    

DOI:10.1002/mrc.1260290204

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractComplexes of the types Pt(L)Cl2, [Pt(L)(D2O)2](NO3)2, [Pt(L)(D2O)(NO3)](NO3), Pt(L)(OD)2, [Pt(L)(D2O)Cl]+and Pt(L)(OD)Cl, where L = ethylenediamine,N,N‐dimethylethylenediamine,N,N′‐dimethylethylenediamine andN,N,N′,N′‐tetramethylethylenediamine, were characterized mainly by195Pt and1H (high‐ and low‐field) nuclear magnetic resonance. The NMR spectra were measured in D2O. The dichloro complexes showed a195Pt resonance between −2355 and −2433 ppm (relative to Na2PtCl6) whereas the diaqua compounds absorbed at lower field from −1821 to −1977 ppm. The signals of the monoaqua‐monochloro species were observed at intermediate field between −2030 and −2173 ppm. The dihydroxo complexes showed a resonance at lower field (about 100 ppm) than the diaqua compounds, whereas the monochloro‐monohydroxo species absorbed at about 50 ppm from the monoaqua‐monochloro species. The monoaqua‐mononitrato compounds with only two ligands absorbed at about −20 ppm from the diaqua species. The high‐field proton NMR spectra of the complexes were also measured. The195Pt–1H coupling constants were obtai

ISSN:0749-1581    

DOI:10.1002/mrc.1260290205

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractRemarkably large (>10 ppm)13C NMR chemical shift differences are observed in solution and in the solid phase betweenorthoaromatic carbons of structurally analogous dibenzodiaza‐18‐crown‐6 ethers and their 9‐membered ring counterparts. On the basis of geometries deduced from1H1H NOESY results, the upfield13C chemical shifts in the 18‐membered systems are attributed tociscoplanar interactions between the terminal carbons of these torsional networks. Overall mobilities of 9‐ and 18‐membered ring systems are examined via13C spin–lattice r

ISSN:0749-1581    

DOI:10.1002/mrc.1260290206

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractγgaucheEffects of 17β‐ and 7α‐substituted 14α‐steroids were studied by1H and13C NMR spectroscopy. A linear correlation was found between the1H chemical shift of H‐12β and the13C chemical shift of C‐12 for C‐17β‐substituted steroids and between the chemical shifts of H‐14α and C‐14 in C

ISSN:0749-1581    

DOI:10.1002/mrc.1260290207

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractProton chemical shifts for the C‐18, C‐21, CO2CH2CH3and CO2CH2CH3protons of epimeric ethyl esters of 20(R,S)‐hydroxy‐23‐norcholanoic acids were measured in deuteriochloroform and pyridine‐d5. The observed solvent shifts due to specific OH—pyridine hydrogen‐bonded complexes allowed the quantification of the epimeric mixtures by analysis of the pyridine‐d51H NMR spectra. The main features of the pyridine‐induced shifts are rationalized in terms of the preferred conformations for the 20R‐ and 20S‐epimers, which are predicted by molec

ISSN:0749-1581    

DOI:10.1002/mrc.1260290208

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractA survey of the one‐bond upfield18O isotope effects on13C NMR chemical shifts shows that a linear relationship exists between the magnitude of the isotope shift and the17O NMR chemical shift for the corresponding oxygen atom in the molecule. The relationship holds over the entire range of functional groups to a significance level of>99.999% for 66 pairs of data points. This relationship permits an estimation with confidence of the general magnitude of an18O isotope shift in13C NMR, simply from a knowledge of the17O NMR chemical shift for an oxygen atom of interest. Extrapolation of this relationship anticipates observation of downfield isotope shifts and may assist in an explanation of this rare and unusual phenomenon in NMR spectroscop

ISSN:0749-1581    

DOI:10.1002/mrc.1260290209

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe conjugative ability of a spirocyclopropane on 4‐en‐3‐one steroids was studied with the help of13C NMR and two‐dimensional experiments such as COSY and NOESY. The conformational analysis of the A ring of these compounds indicates a ‘normal’ (1α,2β)‐ half‐chair conformation rather than the expected ‘inverted’ (1β,2α)‐ half‐chair conformation. Application of the modified McConnell equation for the shielding influence of the cyc

ISSN:0749-1581    

DOI:10.1002/mrc.1260290210

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe17O NMR chemical shift data for 23 9‐fluorenones in acetonitrile at 75°C are reported.17O NMR data for the 3‐substituted 9‐fluorenones are correlated with17O NMR data for 4‐substituted acetophenones. Chemical shift data for 1‐halogeno‐9‐fluorenones are deshielded relative to the 3‐isomers, suggesting important repulsive van der Waals interactions. The keto carbonyl signal for 9‐fluorenone‐1‐carboxylic acid is substantially shielded, as expected, from intramolecular hydrogen bonding. The data for several multi‐substituted 9‐fluorenones demonstrate that substituent effects are addi

ISSN:0749-1581    

DOI:10.1002/mrc.1260290211

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY