摘要:

AbstractNatural abundance13C NMR chemical shifts have been experimentally determined for a series of mesoionic thiazolo[3,2‐a]pyrimidine‐5,7‐diones. The spectral data are compared with those of related mesoionic dihydrothiazolo[3,2‐a]pyrimidine‐5,7‐diones and mesoionic 1,3,4‐thiadiazolo[3,2‐a]pyrimidine‐5,7‐diones. Resonable correlation between the observed13C NMR chemical shifts and CNDO/2 total charge densities have been obtained for the different carbon atoms of 8‐methylthiazolo[3,2

ISSN:0030-4921    

DOI:10.1002/omr.1270210902

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractThe spin‐lattice relaxation rates of the aromatic, alkene, hydroxyl, methine and methyl protons of 19 steroid derivatives have been measured using the null point method. A simple procedure is described whereby theR1values of molecules which have different motional tumbling rates can be directly inter‐compared, and it is shown that such ‘normalized’ relaxation data can provide novel insight concerning both the geometry and the local molecular motion of these substances in s

ISSN:0030-4921    

DOI:10.1002/omr.1270210903

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractA new bicyclic system, 3,7‐diazabicyclo[4.1.0]heptane, has been prepared from 3‐(ethoxycarbonyl)‐7,3‐oxazabicyclo[4.1.0]heptane by reaction with sodium azide and reduction of the resulting tosyloxy azide with lithium aluminum hydride. The molecule can exist in four stereoisomeric half‐chairs, depending on the configuration of the two nitrogen atoms. Half‐chair ring reversal and piperidine nitrogen inversion are fast on the NMR time scale at all observed temperatures. Inversion of the secondary aziridine nitrogen becomes slow as the temperature is lowered (Tc= −10°C). Complete analysis of the1H spectrum was possible with the 1,5,5‐trideuteriated analog. At slow exchange, two aziridine invertomers are present with anexo/endoratio of approximately 0.7 in toluene‐d8, 0.7 in CH2Cl2and 1.7 in CHCl3/CH2Cl2. The free energy of activation for nitrogen inversion is 13.2 kcal mol−1at

ISSN:0030-4921    

DOI:10.1002/omr.1270210904

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractThe routine use of the INEPT pulse sequence is shown to be the method of choice for the assignment of multiplicity from13C NMR spectra where no prior information about the1J(CH) coupling constants is available, or where these are expected to vary over a large range. This technique is illustrated using spectra obtained from polyhalogenated monoterpenes isolated from the red algaPlocamium angustum, which have1J(CH) values varying from 127 to 203 Hz.

ISSN:0030-4921    

DOI:10.1002/omr.1270210905

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

Abstract3‐Aryl‐2‐thioxo‐4‐oxazolidinones and 3‐arylrhodanines have been studied for magnetic non‐equivalence of diastereotopically related proton and13C nuclei in rotational isomers, and for steric interactions between the aryl and heterocyclic moieties of these compounds. For the majority of rotational isomers the barriers to internal rotation about the aryl CN bond were>100 kJ mol−1, due to the steric bulk of the thiocarbonyl group. Chemical isolation of several of the diastereomers was achieved. The enhanced steric effect and the difference in the electronic effect of the sulphur atom in relation to the oxygen atom appeared to have no influence on the small chemical shift differences of the rotational isomers, detected for some1H a

ISSN:0030-4921    

DOI:10.1002/omr.1270210906

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractSolvent shifts of a series of alkanes have been studied in perfluorohexane, carbon tetrachloride and diiodomethane. The methylene proton resonances for longer alkyl chains are shifted downfield in perfluorohexane, but upfield in diiodomethane. It is suggested thatn‐alkanes have a tendency to adopt folded structures in solution, the degree of folding forn‐alkane chains in perfluorohexane being larger than that in diiodometh

ISSN:0030-4921    

DOI:10.1002/omr.1270210907

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractThe1H NMR chemical shifts and the spin‐spin coupling constants of the non‐exchangeable protons of theN‐terminal 13‐residue C‐peptide of ribonuclease A, obtained by cleavage of the enzyme with cyanogen bromide, have been measured in a 5 mM solution in D2O (pH 3.0, 24°C) at 360 MHz. The titration parameters for end groups (Lys‐1 and homo‐Ser‐13) and side chains (Lys‐1, Glu‐2, Lys‐7, Glu‐9 and His‐12) have been determined. The chemical shifts, their temperature coefficients and the vicinal coupling constants,3J(HNCH‐α), for the exchangeable NH protons have been measured in a 5 mM solution in D2O/H2O (1:9 v/v) at pH 3.0. An assignment of observed signals to individual residue protons based on characteristic shifts, standard double resonance experiments, spectral simulations and titration shifts is proposed. All experimental evidence indicates that under the conditions studied the C‐p

ISSN:0030-4921    

DOI:10.1002/omr.1270210908

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractNatural abundance15N NMR spectroscopy has been used to investigate the effect of pH on the15N chemical shifts of lysine and of ε‐hydroxymethyllysine. A computer calcualtion which fits the chemical shifts of both α‐and ε‐nitrogen atoms versus pH has been used to predict the pKavalues.15N chemical shifts and some1J(15NH) values of some other amino acids and of their reaction products with formaldehyde are also

ISSN:0030-4921    

DOI:10.1002/omr.1270210909

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

Abstract29Si NMR spectra of theO‐trimethylsilyl (OTMS) derivatives of various methyl α‐ and β‐D‐galactopyranosides have been recorded. The effect of changes in the anomeric configuration provides a means of assigning the resonance of the 2‐OTMS substituent. Whereas the signal of the OTMS group attached at the 6‐position can be assigned readily, those of the OTMS group at the 3‐ or 4‐position cannot be assig

ISSN:0030-4921    

DOI:10.1002/omr.1270210910

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY

摘要:

AbstractThe13C NMR chemical shifts ofm‐ andp‐substituted benzylN,N‐dimethylcarbamates were measured in CDCl3. Themetaandpara13C substituent chemical shifts were analysed by means of dual substituent parameter (DSP) equations. Good correlations were obtained, especially for thepara‐carbon substituent chemical shifts. The computed transmission coefficients, ρIand ρR, are consistent with the general features of the fitting parameters. It has been shown that no significant electron demand is imposed by the CH2OCON(CH3)2

ISSN:0030-4921    

DOI:10.1002/omr.1270210911

出版商:John Wiley&Sons Limited    

年代:1983

数据来源: WILEY