摘要:

AbstractThe intrinsic ASIS of formyl protons inp‐X‐benzaldehydes, dimethylformamide and diphenylformamide in a series of aromatic hydrocarbon solvents have been calculated. These values of Δ¯xαof the formyl protons present excellent correlations in aromatic hydrocarbon solvents, and are factorizable into solute and solvent factorsUxandVα, respectively. TheUxvalues are linearly related to the value of σpof the substituent in the solute. TheVαvalues depend on the substitution pattern of the benzene ring of the solvent

ISSN:0030-4921    

DOI:10.1002/mrc.1270220202

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe14N nuclear quadrupole resonance (NQR) spectra of several nitrogen mustard compounds are reported and analyzed in the framework of the Townes and Dailey theory. For the aniline derivatives, a correlation exists betweenl–σ (wherelis the nitrogen lone pair electron density and σ the average NC sigma‐bond electron density) and the enhanced Hammett sigma constant σ−. An improved correlation is obtained betweenl–σ and σR−, which emphasizes the importance of resonance effects in determiningl–σ. The increase of hydrolysis and alkylation rates with increasing values ofl–σ is in agreement with the identification of the aziridinium ion as the intermediate in aromatic nitrogen mustard hydrolysis and alkylation. A possible correlation is noted between the35Cl NQR spectra for some of the mustards and measures of toxic

ISSN:0030-4921    

DOI:10.1002/mrc.1270220203

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractProton magnetic resonance (1H NMR) was used to studycis‐transisomerization inN‐methyl‐N‐(1‐methylthio‐2‐propenyl)formamide andN‐benzyl‐N‐(1‐methylthio‐2‐propenyl)formamide, two analogs of the thiol form of thiamine. Benzene dilution studies and shift reagent studies were used to make resonance assignments, which indicate that the predominant isomer for each analog has the CC bondtransto the carbonyl oxygen. Shift reagent studies, using Pr(fod)3in CCl4or CDCl3, suggest that the reagent may be bonding to both the nitrogen and oxygen atoms of the substrate. For some of the systems studied, varying ρ at constant temperature had the same spectral effect as varyi

ISSN:0030-4921    

DOI:10.1002/mrc.1270220204

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractOrganometallic rhodium(I) derivatives have been studied by103Rh NMR. The chemical shift range extends from 609 ppm ([Rh.cp.cod]) to 2714.7 ppm ([Rh.fod.cod]). These results are supported by13C and31P NMR results, and give information about the bonding in these derivatives. Most of the complexes contain the cycloocta‐1,5‐diene ligand. For these complexes a linear correlation is observed between δRh and δC (olefinic carbons) (27 points,R= 0.960). For the phosphine derivatives a linear correlation is found between δRh and1J(RhP) and, also, between δRh and parameters characterizing the basicity of the phosphine ligand. The correlation of δRh with ligand properties has been extended to a wider range of complexes by using the ‘influence parameters’ defined previously (10 points,R= 0.947). The sensitivity of δRh to steric factors i

ISSN:0030-4921    

DOI:10.1002/mrc.1270220205

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of fourortho‐ and sevenpara‐quinone methides were assigned using chemical shift and long‐range carbon‐proton coupling information. The carbonyl shifts are compared with those inortho‐ andpara‐benzoquinones. The chemical shifts of the carbonyls of thep‐quinone methides are observed at δ 186.2–186.4 for the threeortho‐di‐tert‐butyl‐substituted compounds and at δ 180.7–181.5 for the fourortho‐oxy‐substituted compounds. In the threeo‐quinone methides withmeta,para‐dioxy substituents, the carbonyl signals are at δ 184.2–185.4. The carbonyl signal of the oneo‐quinone methide with no oxygen substitution is shifted downfield to δ 200.9, apparently as a result o

ISSN:0030-4921    

DOI:10.1002/mrc.1270220206

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractSome shielding calculations, using Pople's SOS model, are reported for B, C, N, F, P and Si as a function of changes in bond length and pyramidal bond angle. In all cases considered, the shielding is predicted to decrease as the bond length increases, which is in line with the available experimental data. The observed temperature variation of the nitrogen and phosphorus shieldings of NH3, PH3and PF3could be accounted for by a decrease in the pyramidal angle at higher temperatures. A similar angular variation for NF3is predicted to cause a shielding variation, with temperature, in the same sense as that reported for NH3and PH3, but opposite to that for PF3.

ISSN:0030-4921    

DOI:10.1002/mrc.1270220207

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of some derivatives of bryonolic acid (1) (D:C‐friedoolean‐8‐en‐3β‐ol‐29‐oic acid) were assigned by means of13C‐enrichment, lanthanide‐induced shifts (LIS) and comparison of chemical shift data between derivatives. The13C‐enriched species of 1, i.e., 1a, 1b and 1c were biosynthesized byLuffa cylindrica(Cucurbitaceae) callus fed with [1‐13C]‐, [2‐13C]‐ or [1,2‐13C2]‐acetate, respectively. Methyl acetylbryonolates 2, 2a, 2b and 2c, methyl bryonolates 3, 3a, 3b and 3c, methyl bryononates 4 and 4a, diacetyl‐3β,29‐diols (3,29‐diacetyl‐D:C‐friedoolean‐8‐en‐β,29‐diol) 5, 5a, 5b and 5c, and 3‐acetyl‐3β,29‐diols 6, 6a and 6b were prepared from 1, 1a, 1b and 1c, and their13C NMR spectra were recorded. The13C concentration of the13C‐enriched species was high enough to exhibit the satellite peaks clearly, and the analysed data were very useful for this study. Thus, total assignments for 2, 3, 4, 5 and 6 were established. It was found that conversion of the methoxycarbonyl group at C‐29 into an acetoxymethyl group caused complex changes in the chemical shifts of the C, D‐ and E

ISSN:0030-4921    

DOI:10.1002/mrc.1270220208

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe simultaneous evaluation of ali pH‐dependent resonance signals (or multiplets) of an NMR titration offers a substantially increased accuracy and significance. The number of linearly independent titration equilibria is determined by graphical matrix rank analysis. The chemical shifts of all pH‐dependent resonance lines are plotted against each other (chemical shift or CS diagrams) indicating whether a single or more titration equilibria are NMR spectrometrically observable and how far they overlap with each other. An iterative curve‐fitting program allowing the simultaneous evaluation of all (pH) curves is available, from which pKvalues and chemical shifts of all species can be calculated. The starting pKvalues for the iteration need only be estimated very approximately (accuracy ±1–2 units). The titration end‐points do not have to be experimentally accessible. The different methods for the simultaneous evaluation of all pH‐dependent NMR signals are exemplified in the31P NMR titration of thiamine pyrophosphate. In this case either the observed resonance lines (two doublets in a broad band proton decoupled spectrum) or the calculated chemical shifts for this AB system can be evaluated. A titration of sodium pyrophosphate was performed and evaluated fo

ISSN:0030-4921    

DOI:10.1002/mrc.1270220209

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe study of a set of 3‐benzylidene‐4‐chromanones, 3‐benzyl‐4‐chromanones, 3‐benzyl‐3‐hydroxy‐4‐chromanones and 3‐benzylchromones (homoisoflavonoids) by13C NMR spectroscopy shows the influence of the structure of these molecules on the chemical shifts of the more characteristic carbon atoms

ISSN:0030-4921    

DOI:10.1002/mrc.1270220210

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

Abstract1H and13C chemical shifts are reported for four peracetylated triglucoses. Assignments are based on the recently proposed two‐dimensional Relayed Coherence Transfer Technique. The chemical shift data were obtained from conventional one‐dimensional NMR spec

ISSN:0030-4921    

DOI:10.1002/mrc.1270220211

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY