摘要:

Abstract15N NMR shielding data are presented for 56 cyclic azines in 0.5 M dimethyl sulfoxide solutions with 0.01 M increments of Cr(acac)3added for each nitrogen atom in the molecules. For the polyazines, the15N signal assignments were based on2J(NH) interactions and some INDO/S‐SOS shielding calculations. The effects of α‐, β‐ and γ‐methyl and conjugated ring substitution on nitrogen shielding are presented and discussed, as are the influences arising from fusion with alicyclic and aromatic rings at various positions. The effects of a second nitrogen atom on the shielding of the first one are shown to be critically dependent on both their relative positions and on the position of fusion of conjugated ri

ISSN:0030-4921    

DOI:10.1002/mrc.1270220402

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

Abstract15N NMR chemical shift data are presented for 14 azolopyridines, together with the results of INDO/S‐SOS calculations of nitrogen shieldings. Previous14N NMR results for some of these compounds are reinterpreted. The14N data and their assignments are shown to be reliable for the indolizine nitrogen atom from arguments based on relative line widths. The pyridine‐type nitrogens are more reliably assigned from the15N spectra combined with the results of the INDO/S‐SOS calculations for individual molecules. A combination of14N and15N NMR spectra, together with the shielding calculations, provides a basis for unambiguous assignments of all the various nitrogen environments consi

ISSN:0030-4921    

DOI:10.1002/mrc.1270220403

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

Abstract15N NMR data are reported for 42 azoles, taken mostly at a standard concentration and in a common solvent (0.5 M dimethyl sulfoxide with a 0.01 M increment of Cr(acac)3for each nitrogen atom present). Signal assignments were assisted by comparison with14N line widths, the use of2J(15N1H) couplings, and shielding calculations obtained by the INDO/S–SOS approach. The generally large differences in nitrogen‐shielding changes permitted rather facile shift assignme

ISSN:0030-4921    

DOI:10.1002/mrc.1270220404

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe chemical shift difference between the carbon atoms in neat dichloroacetic acid is temperature dependent. The temperature dependence was calibrated against the melting points of pure organic compounds to provide an NMR thermometer for13C spectroscopy.

ISSN:0030-4921    

DOI:10.1002/mrc.1270220405

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe13C and1H NMR spectra of α‐methylidene‐β‐hydroxy‐γ‐alkoxy‐pentanoates and ‐decanoates are presented. These data are consistent with a preferred conformation in which an intramolecular hydrogen bond is present. Very characteristic steric shifts in the13C and1H NMR spectra provide an efficient tool for the configurational assignment for this cl

ISSN:0030-4921    

DOI:10.1002/mrc.1270220406

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractProton spin–lattice relaxation rates (R1values) have been measured, at 400 MHz, for a number of 2‐methyl‐ and 2,2‐dimethyl‐substituted 4,6‐diamino‐1‐aryl‐1,2‐dihydro‐S‐triazines. These compounds have high barriers to internal rotation about the aryl CN bond, and exist in solution as mixtures of enantiomeric or diastereomeric rotational isomers. Diastereotopically related 2‐methyl groups in enantiomeric rotamers, and 2‐methyl and 2‐methine protons in diastereomeric rotamers, typically have different relaxation rates. In favourable circumstances this information may be used to identify the individual rotamers. Unequivocal direct identification of rotamers may be obtained from nuclear Overh

ISSN:0030-4921    

DOI:10.1002/mrc.1270220407

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractNitrogen‐14 nuclear quadrupole resonance (NQR) spectra for eleven local anesthetics in the solid state are reported and analyzed using the Townes and Dailey approach. The changes in the electron distributions at various nitrogen sites, produced by protonating the tertiary amino nitrogen, are discussed and shown to be in general agreement with expectations based on the increased electrophilic character of the protonated amino grou

ISSN:0030-4921    

DOI:10.1002/mrc.1270220408

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractA detailed analysis of the13C NMR spectra oftrans‐stilbene and ten deuteriatedtrans‐stilbenes has been undertaken. Some unusual deuterium isotope effects on carbon–hydrogen spin–spin coupling constants could not be explained by the ordinary primary and secondary isotope effects. The positive and negative changes ofnJ(CH) were interpreted in terms of a steric effect, the vibrational influence of the CD bond and thepara‐effect induced by deuterium. In this respect, deuterium behaves as a real substituent with electronic properties different from those of hydrogen. The deuterium isotope effects on13C NMR chemical shifts and carbon–deuterium coupling constants have also be

ISSN:0030-4921    

DOI:10.1002/mrc.1270220409

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractStudies were carried out in order to determine the nature of a peculiar solvent effect observed between acetone and 2‐methoxy‐5‐aminopyridine. It is concluded that a molecular complex is formed due to specific interactions that take place between the solute and solvent. This molecular species is sufficiently long‐lived to produce two separate NMR

ISSN:0030-4921    

DOI:10.1002/mrc.1270220410

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY

摘要:

AbstractThe33S chemical shifts, δ CS 2, and the line widths of selected sulphones, sulphoximides, sulphimides, sulphides and sulphonium ions were measured at 23.009 MHz. δ CS 2increased with decreasing electronic charge on sulphur. The line width varied from 3–10 ppm for sulphones to 400 ppm for sulphonium ions. The higher geometrical flexibility of five‐membered ring sulphones with respect to the six‐membered ring compounds was reflected in the variations of δ CS 2with methyl substitution. Open‐chain sulphoximides are shielded with respect to the corresponding sulphones, whereas open‐chain sulphimides are deshielded with respect to the cor

ISSN:0030-4921    

DOI:10.1002/mrc.1270220411

出版商:John Wiley&Sons Limited    

年代:1984

数据来源: WILEY