Intermolecular interactions in nuclear magnetic resonance. XI. The ¹³C and proton medium shifts of CH₄ in the gas phase and in solution

Abstract

FRANS H. A. RUMMENS and FRANK M. MOURITS. Can. J. Chem. 55,3021 (1977). The 'H and 13C resonances of methane have been measured at 298 K, both as pure CH, in the gas phase as function of the density as well as at low concentration in solution, using polar, non polar, isotropic, as well as magnetically anisotropic solvents. It is found that both the gas and the solution proton shift data can be readily understood in terms of the Vander Waals shielding ow and the mean-square field due to the dispersive interactions: o w = -BF2. Either a macroscopic reaction field model or a binary collision statistical mechanical model for F2 can be used with an approximately equal degree of success. Whereas the 13C gas phase shifts of CH, are also proportional to the density, the 13C gas-to-solution shifts indicate that, apart from 5, there exists even in non-polar isotropic solvents another effectyhich is not proportional to F2. The present study also includes a new proposal regarding F2, a discussion of anisotropy shielding o, in magnetically anisotropic solvents and a discussion of the effective B parameters ('H and 13C) of CH4 in the gas and the solution state. Chem. 55,3021 (1977). On a mesurk les rksonances de 'H et 13C du mkthane a 298 K sous forme de CH, pur en phase gazeuse en fonction de la densitk ainsi qu'a faible concentration en solution utilisant des solvants polaires, non-polaires, isotropes aussi bien que magnktiquement anisotropes. On a trouvk que les donnkes de dkplacement chimique des protons pour le gaz et les solutions peuvent etre facilement expliqukes en termes du blindage de Van der Waals ow et du moyen du carrk du champ dB a des interactions dispersives: ow = -BF2. On peut utiliser soit un modele de champ de &actions macroscopiques ou un modele de mkchanique statistique par collision binaire pour F 2 et l'on a alors des chances approximativement kgales de succes. Alors que les dkplacements 13C en phase gazeuse du CH4 sont aussi proportionnels a la densitk, les dkplacements de 13C qui se produisent lorsque I'on passe du gaz vers des solutions indiquent qu'il existe, en plus de o, mt me dans des solvants isotropes non-polaires, un autre effet qui n'estpas pro- . (3) on the 13C solution shifts of a number of olefins, no other systematic study seems to have been undertaken. This situation appears precarious, because 13C solvent shifts can now be estimated as being of very considerable magnitude; lack of knowledge of these effects can well precipitate errors of interpreta-'Publication was delayed at the author's request. tion in general 13C work. It was decided to study the medium shift effects of CH, to help fill in the aforementioned gap. Methane was chosen for several specific reasons. Firstly, it allows a study in the gas phase as function of density as well as in the liquid phase as gas-to-solution shifts. Secondly, the carbon being at the centre of mass, the site factor complications (ref. 4; see also pp. 46-50 of ref. 1 for a further discussion of this effect) are eliminated for the 13C shifts. Finall...

Xenon NMR: chemical shifts of a general anesthetic in common solvents, proteins, and membranes.

“…Phospholipid vesicles were prepared in aqueous solution as described (10 (2). These include a contribution from the bulk susceptibility ofthe sample, the effects of electric fields generated by any permanent dipole moments ofthe solute or solvent, the effect of any magnetic anisotropy of the solvent, and the "van der-Waals" term which arises in the dispersive and repulsive solute-solvent interactions.…”

“…We have observed solvent-dependent shifts over a range of ca. 200 ppm, a range that is much larger than the solvent shifts of 13C and 19F (2,3).…”

A Collection of Dispersion Induction DI, Electrostatic ES, and Hydrogen Bonding α1 and β1 Parameters for 380 Solvents and What They Say on Solvent Effects on Rates, Equilibria, and Spectra

“…For properties 12–14, the approximation on repulsive interactions appears less valid, since the determination coefficients are significantly lower ( r 2 = 0.821 to 0.856). Xenon and methane have no permanent dipole moment, thus the solvent effect originates only from dispersion and repulsive forces. − Deviations from the correlations of NMR shifts with DI might be ascribed to variable repulsive interactions.…”

Reaction field model with free volume for the NMR chemical shift of129Xe dissolved in organic solvents

“…(1)Here o-a is the contribution from the magnetic anisotropy of the solvent, o'e2 is the shielding from the permanent dipole moment of the solvent, cr e is the reaction field of the solvent due to the permanent dipole moment of the solute, tr w comes from the dispersion term of the Van der Waals interaction, and Crup is from the repulsive portion of the Van der Waals interaction. Rummens[27,29] showed that for many polar solvents the o'e2 contribution is negligible. Since the local dipole moments in the polymers studied here are relatively weak, this contribution will be neglected, cr e is zero in this case because xenon has no permanent dipole moment.…”