摘要:

AbstractThe base‐catalyzed NH2exchange reactions of acetamide and thioacetamide were studied by15N nuclear magnetic resonance spectroscopy by the use of line‐shape analysis. The15N NMR spectra of these primary amides at intermediate exchange rates were broad doublets, which indicated that the two amide protons were exchanging at different rates. The line‐shape analysis indicated that the ratio of exchange rates was 6±1 for acetamide and 3±1 for thio

ISSN:0030-4921    

DOI:10.1002/mrc.1270180302

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractA new method of differentiating between the different mechanisms operative for13C solvent effects is proposed. This approach, in which the13C solvent shifts of C‐1 oftert‐butylcyclohexane are selected for the reference solvent shifts, allows the study of13C solvent shifts measured from an internal TMS reference. Using this method, the solute factor related to the van der Waals contribution can be estimated, and specific solvent effects other than the van der Waals effect can also be detec

ISSN:0030-4921    

DOI:10.1002/mrc.1270180303

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractA13C NMR study of a number of substituted 1,5‐benzodiazepin‐2‐ones has been carried out, and shows that this technique is one of the rare spectroscopic methods which allows an unambiguous identification of the number and nature of the isomers formed in the condensation of a β‐ketoester with a substitutedO‐phenyl

ISSN:0030-4921    

DOI:10.1002/mrc.1270180304

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe13C NMR spectra of the diterpenoid aminoglycoside wedeloside and certain of its derivatives, representatives of a new kaurenoid series, have been assigned. Shift calculations and labelling experiments have established a general substituent additivity relationship for chemical shifts in kaur‐16‐enes which allowed the reassignment of certain13C resonances in the previously reported spectra of other kaur‐16

ISSN:0030-4921    

DOI:10.1002/mrc.1270180305

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe acidity constants of bothZandEconformational isomers of fiveN‐nitroso‐N‐alkyl‐α‐amino acids, ONN(R1)CH(R2)COOH, are determined by the observation of selected pH titrated1H NMR signals. For two glycine derivatives (1, R1CH3, R2H, ONSar; 2, R1C2H5, R2H, ONEtGly) and two alanine derivatives (3, R1CH3, R2CH3, ONMeAla; 4, R1C2H5, R2CH3, ONEtAla) theEisomers appear to be stronger acids than theZwhile for the third alanine derivative (5, R1n‐C3H7, R2CH3, ONPrAla) the opposite is observed. These results, also including anisotropy effects associated with the NNO group, are discussed in terms of conformations. A 7‐membered ring conformation with an NO…HOOC intramolecular hydrogen bond is proposed to be statistically impo

ISSN:0030-4921    

DOI:10.1002/mrc.1270180306

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractA general method for the assignment of DNA fragment proton resonances, especially for the sugar protons, has been presented and used to interpret the 400 MHz proton spectra of dApTpGpT and dApCpApTpGpT in neutral aqueous solution. Only fine splittings of about 3 Hz are observed in the H‐2″ resonances, and the total splitting is larger for the H‐2′ (≈29 Hz) than for the H‐2″ (22–23 Hz) multiplets. The purine and pyrimidine resonances can be distinguished on the basis of the H‐2″ and H‐2″ chemical shifts. The resonances of the H‐2′ and H‐2″ protons (above and below the sugar plane, respectively) of dA and dG exhibit chemical shifts of 2.65—2.80 ppm, while those of dC and dT residues are located at higher fields between 1.95 and 2.40 ppm. At high temperature (≥60°C), δH‐2′>YδH‐2″ for the purine family, while δH‐2′ « δH‐2″ in the case of the pyrimidine family. Except for the terminal residue, the H‐3′ resonances of dA and dG are located at lower fields compared with those of the dC and dT residues. The same is true for the H‐4′ resonances. In general δA1′>δG1′and in the case of self complementary duplexes the H‐1′ and H‐2′ chemical shift variation

ISSN:0030-4921    

DOI:10.1002/mrc.1270180307

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe methylene, methine and methyl protons at C‐2 and C‐3 from the dioxolane moiety in 2‐methyl‐1,4‐dioxaspiro[4.5]decane constitute an ABMX3coupling system. The analysis data obtained and, also, the application of the Karplus rule to the value of theJ(AB) vicinal coupling constant, confirm the axial orientation of the A methine proton and the pseudoequatorial orientation of the B methylene proton. These findings agree with a ‘half‐chair’ conformation of the 1,3

ISSN:0030-4921    

DOI:10.1002/mrc.1270180308

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe proton NMR spectrum of benzo[b]furan has been investigated in the nematic phase of a liquid crystal. Dipolar couplings obtained from the spectral analysis have been used to derive the interproton distance ratios. The phenyl ring geometry differs from that in benzo[b]thiophene. The deviations have been explained in terms of bond polarization effects.

ISSN:0030-4921    

DOI:10.1002/mrc.1270180309

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractThe assignment of all ring carbons of 37 derivatives of 1,3,4‐oxa‐ or thiadiazoles and of seven isosydnones is described. In some cases,13C‐labelled compounds were used. The analysis of substituent effects and the calculation of charge densities of some of the derivatives suggest that the two nitrogen atoms form a protective screen against electron perturbation and play the role of an ‘electronic buffer’. A notable variation of chemical shifts could be observed only when oxygen is replaced b

ISSN:0030-4921    

DOI:10.1002/mrc.1270180310

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY

摘要:

AbstractCarbon‐13 NMR spectra were measured for 25 methyl esters of aliphatic dichlorocarboxylic acids for substituted propanoic to hexanoic acids. Observed13C shifts are compared with calculated shift values obtained from the shifts of the corresponding monochloro esters by applying a simple sum method. The greatest failures from additivity are observed for αβ and αα substituted carbons. The combined effects of two chlorine substituents were determined, and compared with those obtained from chlorine substituent effects in monochloro esters by assuming additivity. The trends displayed by the combined effects, and also by the non‐additivity effects, are di

ISSN:0030-4921    

DOI:10.1002/mrc.1270180311

出版商:John Wiley&Sons Limited    

年代:1982

数据来源: WILEY