摘要:

AbstractAn individual assignment of certain peaks in the proton and13C NMR spectra of bilirubin and of bilirubin dimethyl ester is described. The assignment was achieved through the spectra of vinylneoxanthobilirubinic acid and by off‐resonance decoupled13C spectra of bilirubin dimethyl ester. The signals due to theendoandexovinyl groups were separately assigned. This assignment allows a rational interpretation of previously obtained spin‐lattice relaxation times of the vinyl carbon peaks. The two vinyl groups are found to differ considerably in their motional correlation t

ISSN:0030-4921    

DOI:10.1002/mrc.1270130112

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

Abstractcis(1‐H, 8a‐H)‐1‐Methylperhydro‐oxazolo[3,4‐a]pyridine andcis(1‐H, 8a‐H)‐1‐methylperhydrothiazolo[3,4‐a]pyridine both adopt exclusively thetrans‐fused conformation in carbon tetrachloride solution at room temperature. Both parent unsubstituted systems exist under similar conditions as equilibria containingc.67% (oxazolo compound) and 64% (thiazolo compound) of thetrans‐fused conformation. In marked contrast to these similar positions of conformational equilibria in both systems thetrans(1‐H,8a‐H)‐1‐methylperhydrooxazolo[3,4‐a]pyridine exists asc.73%trans‐fused in equilibrium with acis‐fused conformation whereas thetrans(1‐H, 8a‐H)‐1‐methylperhydrothiazolo[3,4‐a]pyridine exists almost exclusively in acis‐fused ring conformation. These differences in conformational equilibria are expla

ISSN:0030-4921    

DOI:10.1002/mrc.1270130113

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractProton‐coupled nitrogen‐15 NMR spectra of urea,N‐methylurea,N,‐N′‐dimethylurea,N‐methyl‐N′‐benzylurea andN‐phenylurea have been obtained at natural abundance level in neutral, basic and acidic solutions at 25°C. Base‐catalyzed NH proton exchange of the NH2group ofN‐methylurea in water was found to be 1.5 times faster than that for the ‐NH‐ group, while the corresponding acid‐catalyzed exchange is 7.5 times faster. Comparison of urea andN,‐N′‐dimethylurea in water shows urea to be 10 times faster in base but 2 times slower in acid. The ratio of the base‐catalyzed NH proton exchanges of the two ‐NH‐ groups ofN‐methyl‐N′‐benzylurea in dimethyl sulfoxide is close to unity, whereas the CH3NH‐ group exchanges 4 times faster in acid. Similarly, the C6H5NH‐ group ofN‐methyl‐N′‐phenylurea exchanges 50 times faster than the CH3NH‐ group in base and about 3 orders of magnitude slower in acid. The re

ISSN:0030-4921    

DOI:10.1002/mrc.1270130114

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe13C and31P NMR spectra of the triply13C labelled tribenzoylphosphine [] oriented in a nematic phase have been recorded. From the spectral analysis one obtains the average CPC valence bond angle value (95.9°± 0.2), and the phosphorus chemical shift anisotropy Δσ(σ∥︁– σ⊥) which is equal t

ISSN:0030-4921    

DOI:10.1002/mrc.1270130115

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractThe vicinal coupling constant,J(12), between the vinyl CH and the ring CH protons in vinylcyclohexane was calculated from a ‘partial molecule’ six‐spin system. The 100 and 270 MHz results are in good agreement; those at 60 MHz were, however, still inaccurate in this approximation.J(12) increases with increasing solvent polarity and decreasing temperature. The energy difference between the s‐transandgaucheconformers in both C2Cl4and perdeuterioacetone solvents is 879 ± 167Jmol−1(210±40 cal mole−1). The s‐transconformer is the most stable, in contrast to the isoelectronic cyclohexylcarboxyaldehyde where thegaucherotamers are

ISSN:0030-4921    

DOI:10.1002/mrc.1270130116

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

摘要:

AbstractAddition of small amounts of [Gd(2 : 2 : 1)]3+cryptate to aqueous solutions containing111Cd2+or formamide decreases metal nuclide or nitrogen‐15 spin‐lattice (T1) relaxation times without affecting cadmium or nitrogen chemical shifts. This cryptate is thereby demonstrated to have substantial promise for greatly decreasing the time necessary to obtain natural abundance metal nuclide or15N NMR spectra with satisfactory signal‐to‐noise ratios for many compounds with long metal or15N relaxatio

ISSN:0030-4921    

DOI:10.1002/mrc.1270130117

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY

ISSN:0030-4921    

DOI:10.1002/mrc.1270130101

出版商:John Wiley&Sons Limited    

年代:1980

数据来源: WILEY