摘要:

AbstractIn addition to Taft's dual substituent parameter (DSP) and DSP–non–linear resonance (DSP–NLR) models, and Charton's triple substituent parameter (TSP) equation, two second‐order regression models were tested using published data for13C substituent chemical shifts of the C‐4 atom in 1,4‐disubstituted benzenes. The complete data matrix consisted of 14 series with a fixed Y (C‐4) substituent, each with 14 variable X (C‐1) substituents. Second‐order (in the σ ROparameter or in a combination of the σ1and σ ROconstants) models gave results as good as, and in some cases even better than, the DSP–NLR equation; the results of the TSP model were always worse. The whole data matrix was submitted to principal component analysis. Target testing has shown vectors of σ RO, (σ RO)2and σIconstan

ISSN:0749-1581    

DOI:10.1002/mrc.1260300302

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractNMR and mass spectral data are presented in support of the structures of two metabolites of crisnatol, 2‐[(6‐chrysenylmethyl)amino]‐2‐methylpropane‐1,3‐diol, a novel DNA intercalator currently undergoing Phase II clinical trials as an anticancer agent. Elucidation of the structures of the major rat urinary metabolite astrans‐1,2‐dihydro‐1,2‐dihydroxycrisnatol, and the major rat fecal metabolite as 1‐hydroxycrisnatol, using 2D NMR tec

ISSN:0749-1581    

DOI:10.1002/mrc.1260300303

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo 2:1 maleic anhydride–α‐methylstyrene adducts and two naphthalene derivatives were isolated as low molecular weight by‐products of thermal copolymerizations of maleic anhydride and α‐methylstyrene under different conditions. Their structures were deduced by means of1H1H and1H13C shift correlation NMR spectroscopy. The complete1H and13C NMR assignments

ISSN:0749-1581    

DOI:10.1002/mrc.1260300304

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

Abstract13C,17O and14N NMR chemical shift data for a series of 1,3‐indandiones are reported. Linear correlations were established between some chemical shifts and the electron densities for the compounds in question. Chemical reactivity predictions were based on the results obtaine

ISSN:0749-1581    

DOI:10.1002/mrc.1260300305

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractPartial structures of a reference groundwater humic substance were quantified byJ‐resolved two‐dimensional13C NMR spectroscopy applied in its phase‐sensitive variant. The results agree with those obtained by the one‐dimensional techniques DEPT (distortionless enhancement by polarization transfer) and SEMUT‐90 (subspectral editing using a multiple quantum trap), thus demonstrating the accuracy of both methods. However, the two‐dimensional technique is recommended, because quantification is based on only one spectrum. Quantification provides the ratio of different substructures (carbons belonging to ketones, carboxylic acids, different aromatics, carbohydrates, paraffinic C, CH, CH2and CH3groups) and, in combination with elemental analysis, the partition of hydrogen between C and O (83% bonded to C and 17% to O). Also, insight is obtained into the biogenesis of the humic acids. Aromatic moieties probably originate mainly from lignin rather than from other aromatic compounds. CHO moieties mainly belong to carbons in ethers and alcohols and only to a small extent to carbons in carbohydrates, as shown by comparing NMR results with gas chromatographic analysis of the carbohydrate part performed by other workers. The ratio of paraffinic CH:CH2:CH3is about 1:1:1; the high proportion of paraffinic methyl groups cannot yet

ISSN:0749-1581    

DOI:10.1002/mrc.1260300306

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThiourea inclusion compounds of three monosubstituted cyclohexanes were studied by13C magic angle spinning NMR spectroscopy. Variable‐temperature experiments were performed to evaluate the conformational and motional features of the various guest molecules. From a quantitative line‐shape analysis it is found that the halocyclohexanes with chloro and bromo substituents exist predominantly in the axial conformation whereas methylcyclohexane, as in solution, prefers the equatorial position. Generally, it could be shown that within the temperature range investigated the cyclohexane guest molecules undergo ring inversion processes with kinetic parameters almost unaffected by the host latt

ISSN:0749-1581    

DOI:10.1002/mrc.1260300307

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

Abstract1,3‐Dipolar cycloaddition of (E)‐ and (Z)‐arylidene‐1‐tetralone derivatives affordstrans‐ andcis‐spiro‐1‐pyrazolines, respectively, regio‐ and stereo‐selectively in a one‐step reaction. These rearrange into spiro‐2‐pyrazolines on proton catalysis. The relative configurations and conformations of the spiropyrazolines were elucidat

ISSN:0749-1581    

DOI:10.1002/mrc.1260300308

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractA13C NMR chemical shift prediction and spectral assessment program was written in Turbo Prolog. Based on the large data compendium of Ewing it allows the rapid assessment of the spectral–structural relationship for substituted benzene ring

ISSN:0749-1581    

DOI:10.1002/mrc.1260300309

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

Abstract13C NMR spectra were obtained using cross‐polarization methods at temperatures near 5 K to examine the magnetization transfer spin dynamics and the practicality of routinely making low‐temperature measurements as a means for gaining sensitivity. The magnetization transfer rate between protons and carbon was generally found to be more rapid at 5 K than at room temperature, and the proton and carbon relaxation times in the rotating frame were considerably longer. Both conspire to improve the sensitivity of the cross‐polarization experiment. The limiting factor in the ease of executing the experiment rapidly is the value for the proton spin–lattice relaxation time, which in samples with few methyl groups may become much longer than is common at higher temperatures. However, when the methyl group concentration is high, the proton spin–lattice relaxation rate at 5 K may be in the range of seconds, making the low‐temperature experiment a highly sensitive and practical

ISSN:0749-1581    

DOI:10.1002/mrc.1260300310

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

Abstract1H,13C and17O NMR chemical shifts andnJ(H,H),1J(C,H) and3J(C‐6, H‐formyl) spin—spin coupling constants of chlorinated vanillins (3‐methoxy‐4‐hydroxybenzaldehydes) were determined. The variation in the long‐range4J(H,H) value between the formyl proton and anortho‐proton suggests that theortho‐substituent strongly forces the formyl group out of the aromatic plane. This can also be observed by considering the3J(C‐6,H‐formyl) values and the13C and17O NMR chemical shifts. The17O NMR chemical shifts show a linear correlation with the torsion angle of the formyl group calculated by molecular mechanics. The13C and17O NMR chemical shifts of the methoxyl group also possess strong predictive power in estimating the torsional characte

ISSN:0749-1581    

DOI:10.1002/mrc.1260300311

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY