Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1260310701pmid: N/A

Katritzky, Alan R.; Shcherbakova, Irina V.; Mancheño, Balbino; Tack, Robert D.

doi: 10.1002/mrc.1260310702pmid: N/A

The assignment of the proton and carbon signals and conformations of substituted 5,6‐dihydro‐4H‐1,3‐oxazines were determined by the combination of 1H, 13C, COSY and HETCOR spectral data.

Balczewski, P.

doi: 10.1002/mrc.1260310703pmid: N/A

The long‐range coupling constant 4J(31P, C, S, C, 1H) was measured in several diethyl α‐methylthio‐substituted phosphonates and their analogues. A dependence of the 4J coupling on the substituent electronegativity was observed.

Lux, Philippe; Brunet, Francine; Desvaux, Hervé; Virlet, Joseph

doi: 10.1002/mrc.1260310704pmid: N/A

In order to determine the nature and the structure of polymers formed by condensation of alkoxysilanes, a two‐dimensional INEPT double quantum filtered COSY NMR experiment was developed to observe 29Si29Si correlations at 29Si natural abundance. This experiment was tested on a mixture containing a trimer, [(CH3)3SiO]2Si(CH3)2, and a tetramer, [(CH3)3SiOSi(CH3)2]2O. This 2D INEPT DQF COSY experiment was then used to investigate the nature and the structure of the polymers which are formed in the early stages of the condensation reaction of diethoxydimethylsilane (DEDMS) in a DEDMS–water mixture containing a small amount of water at low pH (1.0).

Pan, Kai; Lin, Chiou‐Rong; Ho, Tong‐Ing

doi: 10.1002/mrc.1260310705pmid: N/A

The combination of high‐performance liquid chromatography (HPLC) and ESR spectrometry was used to isolate the free radicals produced by the reaction of a Grignard reagent with 15 substituted α‐Phenyl‐N‐tert‐butylnitrone. Long‐range hyperfine splitting constants (hfsc) were obtained by the resolution enhancement method. Linear correlation studies between hfsc and Hammett σp constants are reported. Dual‐parameter correlations using σR and σI were also studied. The mass spectra for the HPLC‐isolated spin adducts and their fragmentation patterns are reported.

Radeglia, Reiner; Poleschner, Helmut; Haufe, Günter

doi: 10.1002/mrc.1260310706pmid: N/A

The 1H CW off‐resonance decoupled 13C NMR spectra of (E)‐ and (Z)‐cycloalkenes (C5C12) were measured. The higher order 13C NMR multiplets obtained for the unsaturated carbons allow the determination of the vicinal 1H,1H coupling constant between the vinylic protons and thus the assignment of the configuration of the CH2CHCHCH2 fragment.

Brzezinski, Bogumił; Brycki, Bogumił; Maciejewska‐Urjasz, Hanna; Zundel, Georg

doi: 10.1002/mrc.1260310707pmid: N/A

Eleven substituted 2‐diethylaminomethylphenol N‐oxides were studied in CDCl3 solutions by 1H and 13C NMR spectroscopy. The 1H chemical shifts of the intramolecular hydrogen‐bonded proton and the Δ14 values obtained from the 13C signals were considered as a function of the pKa values of the parent phenols. The 1H chemical shift of the hydrogen‐bonded proton shows a maximum at pKa ≈ 7. This result agrees well with the turning point of the curve if Δ14 is plotted as a function of the pKa of the parent phenols. All these results agree well with recently obtained Fourier transform IR results. With the system with the strongest hydrogen bond (pKa ≈ 7) a broad, flat, single‐minimum proton potential or a double‐minimum proton potential with a small barrier is present. With this system the deshielding of the proton in the intramolecular hydrogen bond is strongest.

Iida, Takashi; Chang, Frederic C.; Mushiake, Kumiko; Goto, Junichi; Nambara, Toshio

doi: 10.1002/mrc.1260310708pmid: N/A

Complete 1H and 13C NMR resonance assignments were carried out for six stereoisomeric 6,7‐glycol derivatives of deoxycholic acid as their methyl esters (four being in the 5β‐series and two in the 5α‐series). In addition to conventional 1D NMR methods, 2D shift‐correlated NMR techniques (1H1H COSY, 1H1H NOESY and 1H13C HETCOR) were used for the signal assignments. Several 1H and 13C resonances have been reassigned from those previously reported. Substituent effects of the 6,7‐glycol moieties on the proton and carbon resonances were clarified and used in the structural elucidation of these compounds.

Milne, John

doi: 10.1002/mrc.1260310709pmid: N/A

The temperature and concentration dépendences of the chemical shift of aqueous selenous acid were studied in order to establish a precise relationship between the shift of this convenient reference and that of dimethyl selenide. The chemical shift of saturated H2SeO3 in H2O on the Me2Se shift scale at 20°C is 1300.0 ppm and its temperature coefficient is 0.094 ppm K−1. The relationships to the chemical shifts of Me2Se in CDCl3 and SeO2 in D2O are also discussed. The results permit the correlation of 77Se NMR shifts from several sources.

Li, Geng‐Ying; Xu, Liang; Wu, Xue‐Wen

doi: 10.1002/mrc.1260310710pmid: N/A

Composite pulses that compensate for resonance offset and electric field gradient inhomogeneity are proposed for broadband excitation of pure nuclear quadrupole resonance systems in powders. The excitation band width of the composite pulse sequences was obtained with a numerical calculation procedure and confirmed by 35Cl experimental spectra of powdered NaClO3.