Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1270220901pmid: N/A

Sweeting, Linda M.; Anet, Frank A. L.

doi: 10.1002/mrc.1270220902pmid: N/A

The synthesis of optically active (1R,2R)‐ and (1S,2R)‐2‐deuterio‐2,3‐dihydro‐2‐methyl‐6‐nitrobenzothiophene‐1‐oxide (3 and 4) is described. Several racemic aryl methyl carbinols in the presence of 3 or 4 give different chemical shifts for enantiomeric CH, CH3 and OH protons. These chemical shift differences are larger than those observed in analogous sulfoxide–alcohol pairs without nitro groups. Quinine and cinchonidine cause observable non‐equivalence of methylene and aromatic protons in racemic 4. The magnitude of the diastereomeric shift difference is sensitive to temperature, solvent, concentration, nature of the π system and steric effects.

Pitkänen, Maija; Laihia, Katri; Schulze, Klaus

doi: 10.1002/mrc.1270220903pmid: N/A

The 13C chemical shifts and the carbon–proton coupling constants have been determined for some chlorinated isobutane and isobutene compounds. The one‐bond coupling constants in isobutane derivatives showed a regular increase with an increasing number of γ‐chlorine substituents. The three‐bond coupling constant of the methyl carbon decreased from 4.2 to 2.0 Hz as the number of chlorine substituents in the γ‐position increased. In the isobutene compounds, the vicinal coupling of C‐1 was larger to protons in a group that is trans with respect to a chlorine substituent on C‐1 than to those in the corresponding group cis to the chlorine. The vicinal coupling constants between atoms in geminal groups (on C‐2) seem to be affected by the orientation of the chlorine substituent on C‐1.

Arumugam, S.; Kunwar, A. C.; Khetrapal, C. L.

doi: 10.1002/mrc.1270220904pmid: N/A

Proton NMR spectra of dibenzofuran and dibenzothiophene were investigated in the nematic phase of liquid crystals. Dipolar couplings obtained from the spectral analysis were used to derive the inter‐proton distance ratios. Deviations from planarity were observed in both molecules, and an attempt was made to determine the extent of non‐planarity. Differences in the relative inter‐proton distances in the two molecules are explained in terms of the bond polarization hypothesis and the van der Waals and the covalent radii of the oxygen and sulphur heteroatoms.

Rajendran, G.; Jain, Sampat R.

doi: 10.1002/mrc.1270220905pmid: N/A

Monopropiophenone thiocarbonohydrazone has been isolated in both linear and cyclic isomeric forms. Each form has been shown to isomerize and exist in equilibrium with the other in DMSO‐d6 solution by 1H and 13C NMR spectroscopy. The kinetics of this transformation show attainment of equilibrium in approximately 6 h, with a linear to cyclic configuration ratio of 40:60.

Erdödiné‐Kövér, Katalin; Jászberényi, J. Cs.

doi: 10.1002/mrc.1270220906pmid: N/A

1,3‐Dipolar cycloadditions of diazomethane and diphenyldiazomethane to exo‐2‐methylenecephalosporins are described. A structural study of the products shows that the initially formed 2‐spiropyrazolinocephems form cyclopropanes by the spontaneous loss of nitrogen. ASIS and NOE measurements reveal that the products with different C‐2 configurations are in two different conformations.

Alberts, Vincent; Cuthbertson, Matthew J.; Hawker, Darryl W.; Wells, Peter R.

doi: 10.1002/mrc.1270220907pmid: N/A

Chemical shift and scalar coupling constant data have been obtained for the 1H, 13C and 29Si nuclei in allyl, methally, cis‐ and trans‐crotyl, cis‐2‐methyl‐2‐butenyl and 3‐methyl‐2‐butenyl derivatives of trimethylsilane.

Abraham, Raymond J.; Leonard, Paul; Ulman, Abraham

doi: 10.1002/mrc.1270220908pmid: N/A

The 13C NMR spectra of new hetero‐substituted tetraphenylporphyrin (TPP) molecules have been studied. It was found that most of the carbon chemical shifts are similar to those found in TPP. The similar chemical shifts of the different β‐carbons in S2TPP and in Se2TPP free bases and, moreover, the considerable downfield shift of the α‐carbons of the S(Se)‐rings on protonation are in agreement with the previously suggested theory of inner and outer aromaticity in these porphyrins.

Bar, Raphael; Sasson, Yoel; Blum, Jochanan

doi: 10.1002/mrc.1270220909pmid: N/A

13C NMR spectroscopy was used for the unequivocal analysis of the mixture of products of RuCl2[P(C6H5)3]3‐catalysed transfer deuteriation of benzylideneacetophenone by (a) DCOONa/H2O, (b) HCOONa/D2O and (c) DCOONa/D2O. Signal assignments in the 13C spectra were obtained mainly from the deuterium‐induced 13C isotope shifts. The geminal 13C2H shift of the β‐carbon of deuteriated 1,3‐diphenylpropan‐1‐one is almost twice that for the α‐carbon.

Lyčka, Antonín; Hansen, Poul Erik

doi: 10.1002/mrc.1270220910pmid: N/A

Deuterium isotope effects on the 13C and 15N nuclear shieldings of o‐hydroxyazo compounds are described. Both the direct and the equilibrium contributions were determined. Large direct deuterium isotope effects on 15N nuclear shieldings for 1Δ, 2Δ and 4Δ and negative Δ1J(15NH) [D] values were observed. Isotope effects on 15N nuclear shieldings, because of their magnitudes, are shown to be very useful in determining changes in the azo–hydrazone equilibrium. Isotope effects on 13C nuclear shieldings are smaller, but the effects observed at the carbon resonances of the N‐phenyl ring are likewise very useful in determining the shift in the equilibrium. Deuterium substitution leads in all cases to a shift in the equilibrium so that the content of the predominant form of the protio compound is increased.