摘要:

AbstractThere is an abundance of information on closed‐shell compounds containing sulphur linked to nitrogen; much less, of course, is known about free radicals containing this moeity. This review describes the wide variety of these radicals, their remarkable stability, the characteristic values of their ESR parameters, their electronic structures and their potential application

ISSN:0749-1581    

DOI:10.1002/mrc.1260280302

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractDynamic effects of tetramethyllimonene were studied at low temperatures. Nuclear Overhauser effects measured under optimized conditions at 223 K and the results of 2D correlation experiments allowed the identification of two conformers and the assignment of all the proton and carbon resonances. For the determination of exchange and relaxation rates the method of saturation transfer was applied. At temperatures below 223 K further dynamic effects were recognized. Structural information obtained experimentally was compared with the results of Allinger force field calculations.

ISSN:0749-1581    

DOI:10.1002/mrc.1260280303

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

Abstract13C NMR chemical shifts were determined for all carbons in a number of 1,7,7‐trimethyl‐3‐[(E)‐2′‐arylethenyl]‐2‐oxabicyclo[4.4.0]deca‐3,5‐dienes [aryl = C6H5, C6H4CH3‐p, C6H4F‐p, C6H4Cl‐p, C6H4Br‐p, C6H4CN‐p, C6H4NO2‐p, C6H4OCH3‐p, C6H3(OCH3)2‐m,pand α‐furyl]. Substituent chemical shift (Δδ13C) values for C‐1, C‐3, C‐4, C‐5, C‐6, C‐1′, C‐2′, C‐3′ and C‐4′,8′ were correlated with various Hammett parameters by singleparameter analysis. The correlations revealed that the substituent effects are transmitted across three π‐bonds in conjugation with the aryl ring. Dual‐substituent‐parameter treatment of the substituent chemical shifts revealed that resonance plays a major role in the substituent effect tra

ISSN:0749-1581    

DOI:10.1002/mrc.1260280304

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

Abstract13C NMR data for several linear furanocoumarins are reported. The β, γsynand δ effects of a 5‐oxygenated function on the coumarinic skeleton were measured. A spectroscopic criterion for distinguishing between C‐5 and C‐8 oxygenated, between C‐5 oxygenated, C‐8 alkylated and C‐5 alkylated, C‐8 oxygenated linear furanocoumarins and between C‐5 oxygenated linear or angular furanocou

ISSN:0749-1581    

DOI:10.1002/mrc.1260280305

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe monomer–dimer equilibrium of retinoic acid in carbon tetrachloride was studied by1H and13C NMR spectroscopy. The dimer dissociation constant at 24°C was determined to be 0.38 mM from a fit of the changes in the carboxylic acid carbon chemical shift as a function of concentration. The temperature dependence of the equilibrium constant obtained from the13C NMR signals was used to determine the enthalpy (8.0 kcal mol−1) and entropy (12 cal mol−1K−1) changes for the dimer dissociation process. These results were shown to be more precise than the values obtained from the carboxylic acid proton r

ISSN:0749-1581    

DOI:10.1002/mrc.1260280306

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractHigh‐field NMR studies of (1S, 4R, 6R)‐ and (1S, 4R, 6S)‐1,3,3‐trimethyl‐2‐oxo‐6‐(2‐oxopropyl)bicyclo[2.2.2]octane were carried out by one‐ and two‐dimensional methods. The stereochemical aspects of these molecules were studied through the application of the nuclear Overhauser effect and stereospecific coupling constants. Unambiguous1H and13C chemical shift assignments have been made on the basis of two‐dimensional homonuclear (1H–1H) and heteronuclear (1H–13C) correlation spectroscopy, APT, INAPT and broad‐band

ISSN:0749-1581    

DOI:10.1002/mrc.1260280307

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractPolymeric charge‐transfer complexes with different polymer donors and monomer acceptors were investigated by electron spin resonance spectroscopy. The spin concentrations,g‐values and line widths in the complexes have been determined. The concentration of the paramagnetic charge‐transfer complexes generally increased with increasing strength of the donor‐acceptor tendencies, and exhibited an exponential temperature dependence of spin concentration characteristic of semiconductors. The paramagnetic charge‐transfer complexes were finally transformed into a diamagnetic product; this was confirmed by electronic spe

ISSN:0749-1581    

DOI:10.1002/mrc.1260280308

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractSeventeenN‐substituted 3,4‐dihydro‐2H‐1,3‐benzoxazines [N‐substituent = Et, Pri, But, CH2C6H5or CH(CH3)C6H5] were prepared and their structures studied in the light of13C chemical shifts. The γ effects caused by C(α)‐methyl or C(α)‐phenyl substitution at the heterocyclic ring carbons were found to be valuable structural parameters. By usingN‐tert‐butyl derivatives as models, and by dividing γtoteffects into their components, the rotamer populations due to the rotation around the NC(α) bond could be evaluated. The method also allows the configurational assignment of diastereomericN‐α‐methylbenzyl derivatives. The effect of the half‐chair structure on t

ISSN:0749-1581    

DOI:10.1002/mrc.1260280309

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe self‐association of pyrimidine and its methylated derivatives was studied by measuring the concentration‐dependent changes in proton chemical shifts in deuterium oxide at 35°C. The data were analysed by a dimer model with two parameters. The equilibrium constants give an increasing tendency for self‐association within the series pyrimidine (0.091 ° 0.006 l mol−1)<5‐methylpyrimidine (0.165 ° 0.006 l mol−1) ≈ 4‐methylpyrimidine (0.183 ± 0.005 l mol−1)<4,6‐dimethylpyrimidine (0.410 ± 0.011 l mol−1), and the values of the dimer shifts suggest a stacking‐like arrangement

ISSN:0749-1581    

DOI:10.1002/mrc.1260280310

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY

摘要:

AbstractComplete sets of1H chemical shifts and spin coupling constants of testosterone and 17α‐methyltestosterone were determined by analysis of the 600 MHz1H NMR spectra. The spin coupling constants of the two compounds have similar values, but the substitution of a methyl group at the 17α‐position changes the1H chemical shifts of some protons on the C and D rings: low‐field shifts for H‐12α, H‐14α and H‐16α and high‐field shifts for H‐12β and H‐16β. The two‐dimensional1H‐1H COSY and NOESY methods were used for unambiguous assignments, including those for the signals of H‐16α and H‐16β which are interchanged in the present paper from the assignment reported previously. Two‐dimensional1H‐13C shift correlated spectroscopy was also used to complement the1H and13C assignments. The effect on the13C chemical shifts of methyl substitution at

ISSN:0749-1581    

DOI:10.1002/mrc.1260280311

出版商:John Wiley&Sons, Ltd.    

年代:1990

数据来源: WILEY