Magnetic Resonance in Chemistry

doi: 10.1002/omr.1270210101pmid: N/A

Lewis, P. M. E.

doi: 10.1002/omr.1270210102pmid: N/A

Bertrán, J. Fernández; Rodríguez, Mario

doi: 10.1002/omr.1270210103pmid: N/A

The correlation of the ASIS of the formyl protons of benzaldehyde and six of its p‐X‐derivatives in 12 aromatic solvents show marked deviations. Evidence is presented that these deviations are caused by variations in the shielding of the internal reference protons caused by aromatic solvents. Equations are developed which gauge the effect of TMS on the linear correlations of proton ASIS.

Bertrán, J. Fernández; Rodríguez, Mario

doi: 10.1002/omr.1270210104pmid: N/A

A method is developed to calculate the intrinsic ASIS of TMS protons used as internal reference, based on linear correlation of the ASIS of a group of sensor protons in two fixed aromatic solvents. Several solute systems (p‐X‐benzaldehydes, camphor, α‐Br‐camphor, 5‐X‐furfurals, p‐X‐acetophenones and methyl ketones) are used to calculate a series of intrinsic ASIS values of TMS in 12 aromatic hydrocarbon solvents. The Δα TMS values are used, in turn, to calculate the intrinsic ASIS of CHO protons in dimethylformamide and diphenylformamide, and of the CH3 protons in diethyl ether and diisopropyl ether.

Dostovalova, V. I.; Terent'ev, A. B.; Ikonnikov, N. S.; Freidlina, R. Kh.

doi: 10.1002/omr.1270210105pmid: N/A

Carbon‐13 NMR spectra of 56 long‐chain polybranched carboxylic acids their esters, including chloroand acetoxy‐substituted derivatives, have been studied. An empirical linear two‐parameter equation, relating carbon chemical shifts in α‐branched carboxylic acids and their derivatives to the chemical shifts of the corresponding carbon atoms in analogous hydrocarbons, and to the degree of branching at the α‐carbon atom, \documentclass{article}\pagestyle{empty}\begin{document}$$ {\delta_{\rm x} = {\rm A}\delta_{\rm H}+{B_n}+{C}} $$\end{document} is suggested for the assignment of the signals, where δX is the shift in the acid (ester), δH the shift in its hydrocarbon counterpart and n the degree of branching. The regression coefficients, A, B and C, are given for X=COOH, COOMe and COOEt.

Vitorge, M. C.; Chenon, M. T.; Coupry, C.; Lumbroso‐Bader, N.

doi: 10.1002/omr.1270210106pmid: N/A

Accurate values of iJ(HH) and iJ(CH) were obtained for a series of hydroxy‐and mercaptopyridines and‐pyrimidines. It is shown that the 3J(CH) values provide a valuable criterion for differentiating aromatic from quinoidal structures, and is an easy method for determining N‐methylation or N‐addition sites.

Ryder, Mary T.; Rosenfeld, Stuart M.

doi: 10.1002/omr.1270210107pmid: N/A

The peri protons in a series of 10‐spiroclopropyl‐9,10‐dihydroanthracenes have been shown to have shifts consistent with large (0.43‐0.55 ppm) long‐range shielding effects exerted by neighboring cyclopropyl groups. The shieldings are expected to be sensitive to variations in preferred conformation and, since the range of observed shifts for the five compounds studied is relatively small, it is concluded that all exhibit similar conformational preference.

Risley, John M.; DeFrees, Shawn A.; Van Etten, Robert L.

doi: 10.1002/omr.1270210108pmid: N/A

A series of para‐ and meta‐substituted acetophenones were prepared which were highly labeled with 18O at the carbonyl function. The natural abundance 13C NMR spectra of the compounds were recorded and the 18O‐isotope‐induced shifts of the carbonyl carbon were measured in order to determine possible substituent group electronic effects on the 18O‐isotope shift. The isotope shifts were found to be correlated with a number of properties which demonstrate the molecular basis of the isotope shift. Good correlations were obtained for the isotope shift as a function of σp+, the carbonyl stretching frequency, the carbonyl group bond order, the n→π**transition of the carbonyl group and the chemical shift of the ipso carbon. In contrast, no correlation was observed between the magnitude of the 18O‐induced isotope shift and the 13C chemical shift of the carbonyl carbon. These properties are discussed in connection with the theoretical basis of the isotope shift.

Faure, R.; Galy, J.‐P.; Mahamoud, A.; Vincent, E.‐J.; Galy, A.‐M.; Barbe, J.

doi: 10.1002/omr.1270210109pmid: N/A

Carbon‐13 NMR parameters were determined for some 9‐alkoxy‐ and 9‐alkylthio‐acridines as solutes in DMSO‐d6 or D2O.

Chawla, A. S.; Chunchatprasert, S.; Jackson, A. H.

doi: 10.1002/omr.1270210110pmid: N/A

A variety of alkaloids have been isolated from the seeds of a range of Erythrina species, including dienoid, alkenoid and lactonic derivatives. The 13C NMR spectra of these compounds have been assigned by internal comparisons within this series of related compounds and also by the use of model compounds.