摘要:

AbstractMeasurements of the13C chemical shifts of 2‐alkoxy‐1,3,2‐dioxaphospholanes have allowed the determination of the contribution of the substituent to the α‐, β‐ and γ‐carbon chemical shifts of attached alkyl groups. The preliminary assignments of the signals were made using the following information; relative intensities, variations in coupling constantsJ(31P13C) and the existence of linear correlations between the shifts of carbon atoms in theP‐alkoxy groups and the degree of substitution of the observed carbon or o

ISSN:0030-4921    

DOI:10.1002/mrc.1270130402

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractINDO parameterized calculations ofnJ(19F15N) are reported wheren=1, 2, 3, 4 and 5. The calculations are performed within the sum‐over‐states perturbation and self‐consistent perturbation frameworks. In general, satisfactory agreement between both sets of calculated results and the available experimental data is obtained. All of the1J(19F15N) and4J(19F15N) couplings can be of either sign. Most of the couplings considered are dominated by the contact contribution but the non‐contact interactions can be very important in certai

ISSN:0030-4921    

DOI:10.1002/mrc.1270130403

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of methyl 2‐pyrone‐3‐, 4‐, 5‐ and 6‐carboxylates were studied and the substituent effects on the 2‐pyrone ring were compared with those of some model compounds.1H NMR spectra were also recorded and discussed. The long range13C,1H coupling constants were obtained, discussed and proved useful in signa

ISSN:0030-4921    

DOI:10.1002/mrc.1270130404

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

Abstract13C,1H coupling constants for biphenylene have been obtained from the analysis of the13C NMR spectrum of the natural abundance α‐13C‐ and β‐13C‐isotopomers. The various mechanisms responsible for the observed results are

ISSN:0030-4921    

DOI:10.1002/mrc.1270130405

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThree series of substituted silaalkanes, (i) SiH3CH2X, (ii) MeSiH2CH2X and (III) Me2SiHCH2X, have been prepared (X=Cl, Br, I, NMe2, OMe, SMe), and the shifts and coupling constants extracted from their1H NMR spectra. Coefficients averaged over three rotameric states can be obtained from the first series which are used for the correction of coupling constants resulting from the presence of the electronegative substituents X. With the aid of the Karplus‐Conroy angular dependence of the interproton coupling constants in silaethane† fragments, corrected for electronegative substitution, approximate rotameric populations in series ii and iii were obtained. Except for X=NMe2, there is always a preference for asynclinalX/CH3relationship, even for sandwiched situations (series I

ISSN:0030-4921    

DOI:10.1002/mrc.1270130406

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe conformational equilibrium constants for isomeric methylcyclohexanols (cis‐ andtrans‐1,2‐, 1,3‐ and 1,4‐methylcyclohexanols) have been determined from peak area measurements in the completely proton decoupled low temperature13C NMR spectra of the individual conformers. The13C chemical shifts are discussed in terms of the addit

ISSN:0030-4921    

DOI:10.1002/mrc.1270130407

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractEvidence from the coupling constants and solvent shifts of the protons in cedranone rules out the boat and chair conformations of the cyclohexanone ring. Linear correlation of the solvent shifts of the C‐15 methyl protons of cedranone with those of the α‐methyl groups of fenchone indicates a nearly planar conformation of the cedranone ring. Site factor analysis of the ASIS effect of the methyl protons of cedranone provides conclusive evidence of a quasi‐chair conformation of the 6‐membe

ISSN:0030-4921    

DOI:10.1002/mrc.1270130408

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractIntrinsic temperature dependencies of13C NMR shifts in alkanes bearing one polar C‐αX bond are determined with neopentyl and 4‐tert‐butylcyclohexyl derivatives as conformationally homogeneous model compounds. The increased shiedling for C‐α at higher temperatures can be related to a C‐α—X bond length increase and, for less polarizable CX bonds, essentially to a decrease of solvent polarity on raising the temperature. The use of temperature dependent13C shifts in conformationally mixed compounds for the determination of the equilibrium constants,K, is evaluated withn‐propyl halides; the computer fit of the unknown conformer shifts and the conformational enthalphy difference, δH° to the time averaged shifts yields δH° values which, although converging rather broadly, are in general agreement with literature data. In compounds with higher conformational barriers, such as methoxy‐ and bromocyclohexane, low temperature signal integration yields accurate δG° values; inclusion of shifts above coalescence, however, yields unreliable δH° and δS° parameters. This can only partially be remedied by application of temperature shift corrections obtained from p

ISSN:0030-4921    

DOI:10.1002/mrc.1270130409

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractUsing the carbon assignments of bleomycin A2as well as those of a series of model compounds, the13C NMR assignments of the antitumor antibiotic tallysomycin (TLM) have been made. With the aid of the carbon assignments the metal binding properties of the new antibiotic toward Zn(II) have been investigated.

ISSN:0030-4921    

DOI:10.1002/mrc.1270130410

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

Abstract15N NMR studies on some signly labelled sydnones,N‐acetylsydonimines and their hydrochlorides, as well as those on some sydnonimine hydrochlorides, show that in each case protonation takes place at the exocyclic moiety,\documentclass{article}\pagestyle{empty}\begin{document}$ - {\rm O}^ \ominus - \mathop {\rm N}\limits^ \ominus {\rm COCH}_3 \,{\rm or}\, - \mathop {{\rm NH}}\limits^ \ominus $\end{document}, respectively. Complete assignments of the nitrogen chemical shifts are possible for the labelled compounds, including the isomeric structures ofN‐alkyl–N‐cyanomethyl–N–nitrosoamines to which, unstable, free sydnonimines ar

ISSN:0030-4921    

DOI:10.1002/mrc.1270130411

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY