摘要:

AbstractThe interpretation of the1H,13C and15N NMR chemical shifts and spectral processes in 2‐nitroenamines, studied as neutral molecules and under cationic and anionic activation conditions, is presented in terms of molecular stereochemistry and electron distribution along the main skeleton. A comparison of the latter effects in the cationic and anionic molecules with respect to the neutral molecule allows hypotheses regarding the activity of various reactive centres, i.e. the C‐2 and NO atoms. In the case of cationic activation a variety of products can be synthesized; the regioselectivity of the reaction in acids is rationalized on the basis of the spectral characterization of the reactive species, the structure of which depends on the nature of the substituent on the enamine nitrogen a

ISSN:0749-1581    

DOI:10.1002/mrc.1260250112

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractLow‐temperature13C NMR spectral data have been obtained for equatorial and axial methyl‐, ethyl‐ and isopropylcyclohexane using a high‐temperature cryogenic trapping technique.13C chemical shift differences between major and minor conformations of each compound are discussed in terms of chemical shift theories. A convenient synthesis of deuteriated dichlorofluoro‐ and difluorochloromethane, which are excellent low‐temperature NMR solvents, is als

ISSN:0749-1581    

DOI:10.1002/mrc.1260250113

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractOne‐bond and long‐range two‐dimensional1H/13C NMR experiments allow the unequivocal and simultaneous assignment of13C and1H spectra. On this basis, previous assignments of13C signals of hibalactone have been re

ISSN:0749-1581    

DOI:10.1002/mrc.1260250114

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractFour types of dithiazolidin‐2‐yl radical were selected for dimerization measurements in solution. The radicals had different types of substituents and/or different amounts of strain; ESR measurements for a new dithiazolidinyl radical prepared fromtrans‐cyclooctene are presented. Toluene, diethyl ether and chloroform were used as solvents. Radical concentration measurements incorporated corrections for the variation of theQof the spectrometer cavity with solvent and temperature. It was found that ΔH⊖for the dimerization process is dependent only on the radical s

ISSN:0749-1581    

DOI:10.1002/mrc.1260250115

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

Abstract13C NMR spectra ofcis‐cyclohexyl‐15‐crown‐5 ether in the temperature range 298–173 K have been recorded. A single degenerate conformational process, attributed to cyclohexyl ring inversion, has been detected with a barrier ofca10.3 kcal mol‐1. Sodium ion complexation increases this barrier byca0.5 kcal mol−1, whereas potassium ion complexation has no measurable effect. Spin‐lattice relaxation time results also indicate more effective complexation of sodium ion than potassium ion by the macrocyclic cro

ISSN:0749-1581    

DOI:10.1002/mrc.1260250116

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractA two‐dimensional heteronuclear multiple‐quantum NMR experiment, based on the DEPT pulse sequence, for the simultaneous determination of the nature of proton‐bearing chemical groups together with the measurement and correlation of carbon and proton chemical shifts is presented. Time and computer memory requirements for the proposed experiment are comparable to the acquisition of a two‐dimensional C,H shift correlation spectrum. The data evaluation of the proposed zero‐quantum carbon‐shift correlated spectrum provides a list of chemical groups corroborated with their carbon and proton chem

ISSN:0749-1581    

DOI:10.1002/mrc.1260250117

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

Abstract29and13C NMR spectra of all possible pertrimethylsilylated β‐D‐xylopyranosyl‐substituted methyl 4‐O‐β‐D‐xylopyranosyl‐β‐D‐ XYLOPYRANOSIDES ARE ASSIGNED BY HETERONUCLEAR1H‐X 2D NMR chemical shift correlation experiments, where X = C or Si. It is shown that the29Si NMR spectra can be used for identification of the glycosidation site and ring assignments. The silicon chemical shifts do not follow any simple rule that would al

ISSN:0749-1581    

DOI:10.1002/mrc.1260250118

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractVariable‐temperature solid‐state13C NMR measurements show effects due to molecular motion in spectra of 2,2‐bis[p‐(2,3‐dihydroxypropoxy)phenyl]propane (BADGETOL), which is a derivative of bisphenol‐A diglycidyl ether. Features in the spectra indicate that the motions present may not be characterized by a simple exponentially decaying autocorrelation function (single correlation‐time process), and a study of the coalescence of doublets due to reorientation between non‐equivalent sites strongly suggests that the motions are more properly characterized by a spatially inhomogeneous distribution of single correlation

ISSN:0749-1581    

DOI:10.1002/mrc.1260250119

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe13C NMR characteristics of the polyaminocarboxylate ligands EDTA [(HO2CCH2)2NCH2CH2N(CH2CO2H)2],DTPA (HO2CCH2)2NCH2CH2N(CH2CO2H)CH2CH2N(CH2CO2H)2and NTA [N(CH2CO2H)3] and their Tl(III) complexes are reported. The pH dependence of the13C shifts of the ligands is helpful in understanding the13C coordination chemical shifts, Δδ, but not the thallium‐carbon coupling constantsJ(205TI,13C), which vary markedly for no apparent reason. The anion Tl(DTPA‐5H)2‐contains three non‐equivalent coordinated carboxyl functions and a suggestion is made to account for this lower

ISSN:0749-1581    

DOI:10.1002/mrc.1260250120

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY

摘要:

AbstractThe1H and13C NMR spectra of 1,4‐diazaphenanthrene (benzolfquinoxaline) (1) and some of its derivatives have been fully assigned and most of the coupling constants have been measured. The compounds examined bear a piperidino or methoxy group at the 2‐ or 3‐position, or a chlorine atom at the 2‐, 3‐ or 9‐position. The spectra of theN‐1‐oxides of 1 and of 1,4,5,8‐tetraazaphenanthrene are also given. The synthe

ISSN:0749-1581    

DOI:10.1002/mrc.1260250121

出版商:John Wiley&Sons, Ltd.    

年代:1987

数据来源: WILEY