Solvent effects on <sup>13</sup>C and <sup>17</sup>O chemical shifts of polar molecules. Comparison between experiment and theory

Tiffon, Bernard; Ancian, Bernard

doi:10.1002/mrc.1270160319

Cited by 10 publications

(2 citation statements)

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“…There is no substantial chemical shift change of the methyl peak observed for pure acetone as the temperature is decreased − from 297 to 124 K. However, the chemical shift of the carbonyl peak of pure acetone moves about 3.6 ppm as the temperature is decreased from 188 to 124 K. It has been reported that the 17 O chemical shift of pure acetone moves to higher shielding and the 13 C chemical shift of the carbonyl peak of pure acetone moves to lower shielding as the temperature is decreased. − These shifts have been interpreted as due to a concentration increase of acetone dimers as the temperature is decreased, although the structure of the dimer is still open to debate, with both a cyclic dimer (with two “hydrogen bonds” between a methyl group of one acetone unit and the carbonyl oxygen of another unit) and an electrostatic collision complex (two head-to-tail acetone units in two parallel planes at a distance of about 3.15 Å, with a C···O interaction between the carbonyl oxygen of one acetone molecule and the carbonyl carbon of another acetone molecule). − ,, …”

Section: Variable-temperature 13c Nmr Studiesmentioning

confidence: 99%

“…[47][48][49][50] These shifts have been interpreted as due to a concentration increase of acetone dimers as the temperature is decreased, although the structure of the dimer is still open to debate, with both a cyclic dimer (with two "hydrogen bonds" between a methyl group of one acetone unit and the carbonyl oxygen of another unit) 51 and an electrostatic collision complex (two head-to-tail acetone units in two parallel planes at a distance of about 3.15 Å, with a C‚‚‚O interaction between the carbonyl oxygen of one acetone molecule and the carbonyl carbon of another acetone molecule). [47][48][49][50]52,53 Variable-Temperature 13 C CP-MAS and DP-MAS Studies of (Acetone-1-13 C/SiO 2 + Acetone-2-13 C/SiO 2 ). Variabletemperature (300-129 K) 13 C CP-MAS spectra were obtained on an acetone/SiO 2 (θ ) 0.80) sample prepared from roughly equal quantities of acetone-1-13 C (*CH 3 COCH 3 , 95% 13 C) and acetone-2-13 C (CH 3 *COCH 3 , 99% 13 C).…”

Section: Variable-temperature 13 C Nmr Studiesmentioning

confidence: 99%

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Hydrogen Bonding between Acetone and Silica Gel, as Studied by NMR

et al. 1999

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13C NMR spectra and relaxation parameters (T 1 H, T 1 C, T 1 ρ H, T CH) were measured via CP-MAS and DP-MAS techniques as a function of acetone loading level in acetone/SiO2 samples at 25 °C. T 1 H and T 1 ρ H values were also measured via 29Si CP-MAS experiments. Peak positions and relaxation parameters are averaged by rapid exchange between different acetone interaction sites on the surface. The data were analyzed in terms of a surface equilibrium of adsorbed acetone units between hydrogen-bonding and non-hydrogen-bonding sites. Data analysis by this model yielded the surface concentration of hydrogen-bonding (silanol) sites (1.5 nm-2) and the equilibrium constant (K = 3.0 nm2). Variable-temperature experiments (124−297 K) at three loading levels yielded values of ΔH° (−5.8 ± 0.3 kJ mol-1) and ΔS° (−12.5 ± 0.7 J K-1 mol-1). A self-consistent, qualitative interpretation of measured relaxation parameters is made in terms of the relative mobilities of hydrogen-bonded (less mobile) and non-hydrogen-bonded (more mobile) acetone on the SiO2 surface.

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Section: Variable-temperature 13c Nmr Studiesmentioning

confidence: 99%

Section: Variable-temperature 13 C Nmr Studiesmentioning

confidence: 99%

Hydrogen Bonding between Acetone and Silica Gel, as Studied by NMR

et al. 1999

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Effect of collision interactions on ¹³C nuclear magnetic shielding in monosubstituted benzenes in halogen‐containing solvents

Jackowski

1984

Org. Magn. Reson.

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The 13C nuclear magnetic shielding in benzene and ten monosubstituted benzenes was studied when these compounds were dissolved in cyclohexane, carbon tetrachloride, tetrachloroethylene, methylene bromide and methylene iodide. The results revealed that the observed changes of -C magnetic shielding are dependent on both the solute and solvent molecular properties, although the dependence on the solvent is much more significant. It was also shown that the solvent effects for aromatic carbons are independent of the m electron density distriiution in an aromatic ring. The observed -C deshielding was attriiuted mainly to overlap effects which take place during molecular collisions. INTRODUCI'IONIt is well known that NMR chemical shifts are solvent dependent. Much research has been carried out in this field,14 which reflects the great importance of this problem in NMR spectroscopy as any routine measurement of chemical shifts includes an unknown solvent effect. It has been previously established that the NMR solvent effect (i.e. the change in nuclear magnetic shielding due to the solvent and in the absence of specific interactions'), usolv, consists of terms due to bulk magnetic susceptibility, a,, diamagnetic anisotropy of the solvent molecules, ua, the polar effect caused by the charge distribution in the neighboring solvent molecules, uE, and the so-called Van der Waals effect, a , , which is the only effect (apart from a,,) if the solute and solvent molecules are isotropic and non-polar : '~3 While ub, a, and uE are well defined and recognized, a,,, is usually used to describe the part of the solvent effect that cannot be explained by the previous terms. According to Rummens? the a, contribution is the effect of the dispersion or London forces, including higher order dispersion terms, and also of repulsive and overlap forces. The problem of the Van der Waals term is not so critical for proton chemical shifts, where a , is usually responsible for only a fairly small part of the solvent effect, and can be explained almost quantitatively by the dispersive attraction between molecules.6 Unfortunately, this is not true for the shielding of other nuclei, e.g. the cw term may easily dominate the solvent effect in 13C chemical shifts. However, a complicating feature of this problem is that the origin of a, may be different for various nuclei (e.g. 'H and 13C). There is increasing evidence that the repulsive forces effectively change the shielding constants of heavier nuclei (e.g. lZ9Xe, I9F and C) during intermolecular interaction^.^-'^ This may be the reason why the theoretical calculations of solvent effects based on the solvation model'4 were unable to predict even the proper direction of changes in the I3C magnetic shielding of methyl carbons (cf. the recent experimental results obtained by Tiffon and Ancian"). It seems that each a, effect requires an individual approach before its nature can be understood.Recently we reported the solvent effect on the I3C chemical shifts of some saturated hydrocarbons dissolved in carb...

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¹³C‐NMR‐ und molekültheoretische Untersuchungen zur Wechselwirkung organischer Moleküle mit Kationen; Wechselwirkung von Acetonmolekülen mit Natriumionen

Meiler

Weller

1982

Zeitschrift fuer Chemie

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Solvent effects on ¹³C and ¹⁷O chemical shifts of polar molecules. Comparison between experiment and theory

Cited by 10 publications

References 13 publications

Hydrogen Bonding between Acetone and Silica Gel, as Studied by NMR

Hydrogen Bonding between Acetone and Silica Gel, as Studied by NMR

Effect of collision interactions on ¹³C nuclear magnetic shielding in monosubstituted benzenes in halogen‐containing solvents

¹³C‐NMR‐ und molekültheoretische Untersuchungen zur Wechselwirkung organischer Moleküle mit Kationen; Wechselwirkung von Acetonmolekülen mit Natriumionen

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Solvent effects on 13C and 17O chemical shifts of polar molecules. Comparison between experiment and theory

Cited by 10 publications

References 13 publications

Hydrogen Bonding between Acetone and Silica Gel, as Studied by NMR

Hydrogen Bonding between Acetone and Silica Gel, as Studied by NMR

Effect of collision interactions on 13C nuclear magnetic shielding in monosubstituted benzenes in halogen‐containing solvents

13C‐NMR‐ und molekültheoretische Untersuchungen zur Wechselwirkung organischer Moleküle mit Kationen; Wechselwirkung von Acetonmolekülen mit Natriumionen

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Product

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Solvent effects on ¹³C and ¹⁷O chemical shifts of polar molecules. Comparison between experiment and theory

Effect of collision interactions on ¹³C nuclear magnetic shielding in monosubstituted benzenes in halogen‐containing solvents

¹³C‐NMR‐ und molekültheoretische Untersuchungen zur Wechselwirkung organischer Moleküle mit Kationen; Wechselwirkung von Acetonmolekülen mit Natriumionen