摘要:

AbstractEu(fod)3‐, Yb(fod)3‐ and Pr(fod)3‐induced chemical shifts of the ‘thioaldehydic’ protons in enethial ligands complexed to a cobalt cyclopentadienyl group are unusually large and in the same direction (10–30 ppm downfield per mole of shift reagent per mole of substrate). The shifts of the protons induced by Eu(fod)3and Pr(fod)3in the enethial ligands show an alternation in sign on proceeding away from the sulfur atom. In contrast to the results with the fod reagents, the ytterbium and lanthanum shift reagents Yb(thd)3and La(thd)3caused only small shifts of protons in the 2‐phenylpropenethial ligand. No induced shifts with the Eu or Pr reagents were observed for a cyclopentadienyl cobalt complex of dithioglyoxal. The induced shifts in these enethial complexes may be caused by varying blends of complex formation, contact and pseudocontact shifts. Caution is advised in assigning origins to lanthanide induced shifts in such organomet

ISSN:0030-4921    

DOI:10.1002/mrc.1270221002

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe temperatuure dependence of the vicinal OCH2CH2coupling constant in the six‐membered ring δ‐valerolactone suggests the presence of at least two conformers of unequal energy. Analysis of this temperature dependence by the Wood‐Fickett‐Kirkwood method in six solvents produces free energy differences in the narrow range 0.8–1.4 kcal mol−1, with a mean of 1.0 kcal mol−1and no apparent dependence on solvent polarity. Thus the two conformers, probably the half‐chair and the classic boat, have similar polarities. The analogous four‐ and five‐membered lactones show little or no temperature dependence for their analogous coupling constants, in agreement with the presence of a single conforma

ISSN:0030-4921    

DOI:10.1002/mrc.1270221003

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

Abstract1H and13C NMR spectra of AC–PSer–Gly, Ala–PSer–Gly and Gly–PSer–Phe have been measured and analysed as a function of pD. The NMR parameters of the PSeryl side chain are a function of the sequence. The second titration step of the phosphate group (pK2= 5.7) is much more difficult to detect in Ac–PSer–Gly and Ala–PSer–Gly than in Gly–PSer–Phe. The conformation in which H‐αC‐αC‐βOP forms a planar W‐type arrangement predominates only for Ala–PSer–Gly. In the other two phosphopeptides thegaucheconformations contribut

ISSN:0030-4921    

DOI:10.1002/mrc.1270221004

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe structures of seven polysubstituted alkylpyridines, recently isolated from coal tar, were elucidated using their13C NMR spectra. For tri‐ and tetra‐substituted derivatives the correct isomeric structure was found from their conformity with the proximity effect, i.e. the deviations from additivity when calculating chemical shifts from substituent increments (SCS) for sterically crowded molecules. This effect manifests itself both on the ring and on the alkyl carbon signals, and in most cases shifts their position upfi

ISSN:0030-4921    

DOI:10.1002/mrc.1270221005

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractOxazolidine derivatives of β‐amino alcohols such as ephedrine have been resolved by13C NMR spectroscopy using Eu(hfc)3as a chiral shift reagent. The method is quantitative in the determination of enantiomeric excess, and is advantageous where1H NMR is of limited use owing, for example, to significant line broadeni

ISSN:0030-4921    

DOI:10.1002/mrc.1270221006

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractESR and optical absorption studies are described for a number of copper(II) chelates with aliphatic polyamines, exhibiting both square pyramidal and square bipyramidal coordination around the copper ion. The complexes studied were bis(N,N′‐dimethylethylenediamine)copper(II) sulphate tetrahydrate, bis(N,N′‐diethylethylenediamine)copper(II) nitrate, diaquosulphato(N,N,N′,N′‐tetramethylethylenediamine)copper(II) hydrate, dinitrato(N,N,N′,N′‐tetramethylethylenediamine)copper(II), dichloro(N,N,N′,N′‐tetramethylethylenediamine)copper(II) and dithiocyanato(N,N,N′,N′‐tetramethylethylenediamine)copper(II). The ESR measurements were carried out in methanol, dimethyl sulphoxide, dimethylformamide and pyridine, at room and liquid nitrogen temperatures. The molecular orbital coefficients were estimated assuming an axial symmetry. The parameter χ proportional to the hyperfine constants shows a variation with the solvent for all these complexes. The χ values in solution are lower than the corresponding average χ values reported in the solid state for each complex. The solvent effect and the influence of 4s character in the ground state are discussed. The χ values, either calculated or reported, for a number of copper complexes for [4O], [3O, N], [2O, 2N], [O, 3N]and [4N] environme

ISSN:0030-4921    

DOI:10.1002/mrc.1270221007

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

Abstract13C NMR spectra of some 2,3‐dihydrofurans were measured. Restricted rotation of the bulky aromatic groups ofcis‐2‐aryl‐3‐methyl‐2,3‐dihydrofurans is observed when these groups have substituents in bothorthopositions. Barriers to rotation were deduced from the variations in line widths of the13C NMR signals. Exchange rates are highly affected by the buttressing effect ofmeta

ISSN:0030-4921    

DOI:10.1002/mrc.1270221008

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractFor a series of compounds with NC or NN bonds, the CNDO/S parameterized calculations forQπ, the electronic charge density on the nitrogen atom, and π bond ordersPπprovide evidence for the simultaneous dependence of the15N chemical shift on both of these parameters. The multilinear regressions obtained produce high values for the regression coefficients. The results throw some light on the nitrogen lone pair delocalization mec

ISSN:0030-4921    

DOI:10.1002/mrc.1270221009

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe relative conformation of the aromatic rings and the amide bridge of diethylmethyl‐2‐[p‐(o‐propoxybenzamido)benzoyloxy]ethylammonium bromide has been established by a combined analysis of non‐selective, single‐selective and double‐selective pulse experiments using, as a basis of comparison, the Dreiding molecular model of

ISSN:0030-4921    

DOI:10.1002/mrc.1270221010

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe17O NMR spectra of some esters are discussed and are correlated with13C NMR chemical shift and IR carbonyl streching band data.

ISSN:0030-4921    

DOI:10.1002/mrc.1270221011

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY