Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1270220201pmid: N/A

Bertrán, J. Fernández; Rodríguez, M.

doi: 10.1002/mrc.1270220202pmid: N/A

The intrinsic ASIS of formyl protons in p‐X‐benzaldehydes, dimethylformamide and diphenylformamide in a series of aromatic hydrocarbon solvents have been calculated. These values of Δ¯xα of the formyl protons present excellent correlations in aromatic hydrocarbon solvents, and are factorizable into solute and solvent factors Ux and Vα, respectively. The Ux values are linearly related to the value of σp of the substituent in the solute. The Vα values depend on the substitution pattern of the benzene ring of the solvent molecules.

Buess, M. L.; Bray, P. J.; Sheppard, D. W.

doi: 10.1002/mrc.1270220203pmid: N/A

The 14N nuclear quadrupole resonance (NQR) spectra of several nitrogen mustard compounds are reported and analyzed in the framework of the Townes and Dailey theory. For the aniline derivatives, a correlation exists between l–σ (where l is the nitrogen lone pair electron density and σ the average NC sigma‐bond electron density) and the enhanced Hammett sigma constant σ−. An improved correlation is obtained between l–σ and σR−, which emphasizes the importance of resonance effects in determining l–σ. The increase of hydrolysis and alkylation rates with increasing values of l–σ is in agreement with the identification of the aziridinium ion as the intermediate in aromatic nitrogen mustard hydrolysis and alkylation. A possible correlation is noted between the 35Cl NQR spectra for some of the mustards and measures of toxic and antitumor activity.

Chriss, Derald; Miller, Robert H.; Echols, Richard E.; Vessel, Ellen

doi: 10.1002/mrc.1270220204pmid: N/A

Proton magnetic resonance (1H NMR) was used to study cis‐trans isomerization in N‐methyl‐N‐(1‐methylthio‐2‐propenyl)formamide and N‐benzyl‐N‐(1‐methylthio‐2‐propenyl)formamide, two analogs of the thiol form of thiamine. Benzene dilution studies and shift reagent studies were used to make resonance assignments, which indicate that the predominant isomer for each analog has the CC bond trans to the carbonyl oxygen. Shift reagent studies, using Pr(fod)3 in CCl4 or CDCl3, suggest that the reagent may be bonding to both the nitrogen and oxygen atoms of the substrate. For some of the systems studied, varying ρ at constant temperature had the same spectral effect as varying temperature at constant ρ.

Bonnaire, R.; Davoust, D.; Platzer, N.

doi: 10.1002/mrc.1270220205pmid: N/A

Organometallic rhodium(I) derivatives have been studied by 103Rh NMR. The chemical shift range extends from 609 ppm ([Rh.cp.cod]) to 2714.7 ppm ([Rh.fod.cod]). These results are supported by 13C and 31P NMR results, and give information about the bonding in these derivatives. Most of the complexes contain the cycloocta‐1,5‐diene ligand. For these complexes a linear correlation is observed between δRh and δC (olefinic carbons) (27 points, R = 0.960). For the phosphine derivatives a linear correlation is found between δRh and 1J(RhP) and, also, between δRh and parameters characterizing the basicity of the phosphine ligand. The correlation of δRh with ligand properties has been extended to a wider range of complexes by using the ‘influence parameters’ defined previously (10 points, R = 0.947). The sensitivity of δRh to steric factors is also proved.

Benson, Mabry; Jurd, Leonard

doi: 10.1002/mrc.1270220206pmid: N/A

The 13C NMR spectra of four ortho‐ and seven para‐quinone methides were assigned using chemical shift and long‐range carbon‐proton coupling information. The carbonyl shifts are compared with those in ortho‐ and para‐benzoquinones. The chemical shifts of the carbonyls of the p‐quinone methides are observed at δ 186.2–186.4 for the three ortho‐di‐tert‐butyl‐substituted compounds and at δ 180.7–181.5 for the four ortho‐oxy‐substituted compounds. In the three o‐quinone methides with meta, para‐dioxy substituents, the carbonyl signals are at δ 184.2–185.4. The carbonyl signal of the one o‐quinone methide with no oxygen substitution is shifted downfield to δ 200.9, apparently as a result of hydrogen bonding to the nearby hydroxyl.

Hamdi, B. T.; Reynolds, D. J.; Webb, G. A.

doi: 10.1002/mrc.1270220207pmid: N/A

Some shielding calculations, using Pople's SOS model, are reported for B, C, N, F, P and Si as a function of changes in bond length and pyramidal bond angle. In all cases considered, the shielding is predicted to decrease as the bond length increases, which is in line with the available experimental data. The observed temperature variation of the nitrogen and phosphorus shieldings of NH3, PH3 and PF3 could be accounted for by a decrease in the pyramidal angle at higher temperatures. A similar angular variation for NF3 is predicted to cause a shielding variation, with temperature, in the same sense as that reported for NH3 and PH3, but opposite to that for PF3.

Kamisako, Wasuke; Suwa, Kiyoko; Morimoto, Kayoko; Isoi, Koichiro

doi: 10.1002/mrc.1270220208pmid: N/A

The 13C NMR spectra of some derivatives of bryonolic acid (1) (D:C‐friedoolean‐8‐en‐3β‐ol‐29‐oic acid) were assigned by means of 13C‐enrichment, lanthanide‐induced shifts (LIS) and comparison of chemical shift data between derivatives. The 13C‐enriched species of 1, i.e., 1a, 1b and 1c were biosynthesized by Luffa cylindrica (Cucurbitaceae) callus fed with [1‐13C]‐, [2‐13C]‐ or [1,2‐13C2]‐acetate, respectively. Methyl acetylbryonolates 2, 2a, 2b and 2c, methyl bryonolates 3, 3a, 3b and 3c, methyl bryononates 4 and 4a, diacetyl‐3β,29‐diols (3,29‐diacetyl‐D:C‐friedoolean‐8‐en‐β,29‐diol) 5, 5a, 5b and 5c, and 3‐acetyl‐3β,29‐diols 6, 6a and 6b were prepared from 1, 1a, 1b and 1c, and their 13C NMR spectra were recorded. The 13C concentration of the 13C‐enriched species was high enough to exhibit the satellite peaks clearly, and the analysed data were very useful for this study. Thus, total assignments for 2, 3, 4, 5 and 6 were established. It was found that conversion of the methoxycarbonyl group at C‐29 into an acetoxymethyl group caused complex changes in the chemical shifts of the C, D‐ and E‐ring carbons and those of the methyl carbons linked to these rings.

Lachmann, Heinrich; Schnackerz, Klaus D.

doi: 10.1002/mrc.1270220209pmid: N/A

The simultaneous evaluation of ali pH‐dependent resonance signals (or multiplets) of an NMR titration offers a substantially increased accuracy and significance. The number of linearly independent titration equilibria is determined by graphical matrix rank analysis. The chemical shifts of all pH‐dependent resonance lines are plotted against each other (chemical shift or CS diagrams) indicating whether a single or more titration equilibria are NMR spectrometrically observable and how far they overlap with each other. An iterative curve‐fitting program allowing the simultaneous evaluation of all (pH) curves is available, from which pK values and chemical shifts of all species can be calculated. The starting pK values for the iteration need only be estimated very approximately (accuracy ±1–2 units). The titration end‐points do not have to be experimentally accessible. The different methods for the simultaneous evaluation of all pH‐dependent NMR signals are exemplified in the 31P NMR titration of thiamine pyrophosphate. In this case either the observed resonance lines (two doublets in a broad band proton decoupled spectrum) or the calculated chemical shifts for this AB system can be evaluated. A titration of sodium pyrophosphate was performed and evaluated for comparison.

Kirkiacharian, B. S.; Gomis, M.; Tongo, H. G.; Mahuteau, J.; Brion, J. D.

doi: 10.1002/mrc.1270220210pmid: N/A

The study of a set of 3‐benzylidene‐4‐chromanones, 3‐benzyl‐4‐chromanones, 3‐benzyl‐3‐hydroxy‐4‐chromanones and 3‐benzylchromones (homoisoflavonoids) by 13C NMR spectroscopy shows the influence of the structure of these molecules on the chemical shifts of the more characteristic carbon atoms at positions 2, 3 and 4.