Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1260270101pmid: N/A

Orendt, Anita M.; Michl, Josef; Reiter, József

doi: 10.1002/mrc.1260270102pmid: N/A

15N NMR chemical shifts were measured for a series of substituted 5‐amino‐1,2,4‐triazoles. The assignment of isomeric structures agrees with earlier results obtained with the use of proton‐coupled 13C NMR.

Osborne, Alan G.; Green, Richard; Sadler, Ian H.; Reed, David

doi: 10.1002/mrc.1260270103pmid: N/A

The 360 MHz 1H and 15 MHz 13C NMR spectra of 2, 2′‐biquinoline, 2,3′‐biquinoline and 6,6′‐dimethyl‐2,3′‐biquinoline are presented and assigned. The diamagnetic anisotropic effect of the neighbouring aromatic ring (Dc) and the electrostatic field effect of the nitrogen lone pair (DN) result in characteristic deshielding effects in the 1H NMR spectra of these compounds. The characteristic chemical shift differences (ΔH and Δc) between nuclei at the corresponding position but on different rings is proposed as an additional assignment aid for the 1H and 13C NMR spectra of unsymmetric biaryls and biheteroaryls. The reaction of quinoline and of 6‐methylquinoline with sodium gives the 2,3′‐biquinoline.

Sardella, D. J.; Boger, E.

doi: 10.1002/mrc.1260270104pmid: N/A

The 1H and 13C NMR spectra of several fluorine‐substituted polycyclic aromatic hydrocarbons in which fluorine projects into a bay region were studied. Both protons and carbons of the sterically opposed CH bond show anomalously large F‐induced shifts and couplings to fluorine. The magnitudes of the couplings (particularly the four‐bond CF couplings which average 26 Hz) indicate a large through‐space contribution due to direct overlap between fluorine and CH bond orbitals, whereas the F‐induced shifts seem more likely to stem from diamagnetic anisotropy rather than F‐induced CH bond polarization.

Kupka, Teobald; Pacha, Jerzy; Dziȩgielewski, Jan O.

doi: 10.1002/mrc.1260270105pmid: N/A

The application of various methods of data processing of a raw, untreated free induction decay (FID) to improve the quality of noisy and overcrowded spectra is shown. The use of complex interpolation of fragments of a typical 31P NMR spectrum of humic substances from forest soil in D2O, combined with two‐stage apodization of the FID, results in better defined signals and a higher accuracy of the integration of signals partially overlapped in the initial spectrum. Convolution difference resolution enhancement was used to enhance the spectral resolution of overlapped orthophosphate ion and orthophosphate monoester signals, while the noise was attenuated by a decreasing exponential.

Exner, Otto; Buděšínský, Miloš

doi: 10.1002/mrc.1260270106pmid: N/A

Carbon‐13 NMR spectra are reported for 63 substituted benzonitriles in deuteriochloroform or in its mixture with dimethyl sulphoxide‐d6. The substituent‐induced chemical shifts (SCS) of the CN carbon correlate well with dual substituent parameters (DSP) in the para series but poorly in the meta series, whichever parameters are used. The DSP treatment was found to be inferior to principal component analysis (PCA), using as a probe 29 sets of literature data on α,β‐unsaturated benzene derivatives. Whereas one component is sufficient for meta derivatives, two terms are needed for para derivatives, which are different for the α‐ and β‐positions. The constants derived by PCA could be in principle used to predict further SCS, but their scope must be still explored.

Waterhouse, Andrew L.

doi: 10.1002/mrc.1260270107pmid: N/A

The fully coupled (FUCOUP) correlation experiment was used to analyze conformation and stereochemistry on two dissimilar compounds, strychnine and camphor. This experiment detects the vicinal coupling between hydrogens and carbons, and the magnitude of this coupling is appraised by the presence or absence of cross‐peaks in the spectrum. This correlates with a first‐order approximation of the Karplus torsional angle relationship, although angles near 45° and 135° are not useful. The FUCOUP experiment works better than other related methods because it has no delays that modify the signal intensity of the coupling.

Galache, M. P.; Garcés, P.; Esteban, A. L.; Diez, E.; Guilleme, J.

doi: 10.1002/mrc.1260270108pmid: N/A

The 60 and 100 MHz 1H NMR spectra of γ‐butyrolactone were analysed in detail. The best set of coupling values (Hz ± 0.03) is 3J ABc = 7.86, 3J ABt = 6.27, 3J BCc = 9.52, 3J BCt = 6.86, 4J ACc + 4J ACt = −0.18, 2JA − 2JB = 3.89 and 2JB − 2JC = 4.86 (A, B and C refer to α, β and γ protons, with respect to the ring oxygen, and c and t mean the same and opposite side of the ring, respectively). The 3J values support the conclusion that the molecule is interconverting between two equivalent conformations of near envelope type with the β‐carbon out of the mean plane defined by the fragment COCOC.

Rosenberger, H.; Scheler, G.; Moskvich, Yu. N.

doi: 10.1002/mrc.1260270109pmid: N/A

1H high‐resolution NMR spectra of polycrystalline alkali trihydrogen selenites were measured at 270 MHz using the combination of a multiple‐pulse sequence and magic angle sample spinning. Good resolution of the separate 1H NMR lines belonging to different hydrogen bonds in these crystals was obtained. Correlations between the measured average values of the chemical shift tensor and the parameters characterizing hydrogen bond [R(O…O) and R(H…O)] distances and the deuteron quadrupolar coupling constant e2qQ/h are presented. These correlations are found to be linear, with high correlation coefficients for the ordered protons. The possibilities of designating disordered protons on finding large deviations from the correlations for ordered protons are discussed.

Xue, Yi; Du, You‐ru

doi: 10.1002/mrc.1260270110pmid: N/A

As an electron donor solvent, propylene oxide (PO) forms a hydrogen bond with water in their binary mixture. The repulsion produced by the electrostatic field from the PO…HOH hydrogen bond forces the protons and methyl group of PO to bend away from the O group and results in the approach of these protons into the plane of the three‐membered ring. Consequently, they experience a stronger paramagnetic field from the ring current and their 1H resonances shift to a lower field. The changes of the HCH angle and HCCH dihedral angles of PO in water cause the geminal coupling constant and the vicinal cis coupling constant to decrease and the vicinal trans coupling constant to increase.