Effet de solvant en résonance magnétique nucléaire de <sup>13</sup>C. I. Cas d'un soluté apolaire: <i>n</i>-pentane

Tiffon, Bernard; Doucet, Jean‐Pierre

doi:10.1139/v76-294

Cited by 28 publications

(5 citation statements)

References 8 publications

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“…The aberrations appear outside the limit of the errors due to uncertainties in r , and &/k, but no alternate explanation can be offered. Because of this we have used the o, data based on [2] and the best straight line of Fig. 1; they are given in column 2 of Table 4.…”

Section: Resultsmentioning

confidence: 99%

“…Calculating the site factors for pure n-pentane as S,,, (CH,) = 1.67, S,,,(CH,) = 1.20 and S,,, = 1.00 for the central carbon respectively and dividing these into the observed slopes (see above), shows that the two types of CH, groups must have virtually the same KB values, whereas that for the CH, group must still be substantially larger. Using a , = 10.12 x cm3, 1, = 16.9 x 10-l2 erg and a3 = 34.5 x cm3 (this is actually the value for neopentane (6)) the KB parameters can be calculated using [2]. The om us.…”

Section: -L8 Esu Determined Previously (6)mentioning

confidence: 99%

“…The parameter B is certainly much larger for I3C than for 'H; the parameter K contains only model approximations and can be expected to be independent of the nuclear species investigated. Following [2] one has therefore In the virial model of RBB, and allowing only binary interactions, one has (5) where u is the intermolecular potential, for which the Lennard-Jones (6-12) potential is conveniently chosen:…”

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

Rummens¹,

Mourits²

1977

Can. J. Chem.

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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...

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Section: Resultsmentioning

confidence: 99%

Section: -L8 Esu Determined Previously (6)mentioning

confidence: 99%

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

Rummens¹,

Mourits²

1977

Can. J. Chem.

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“…should reflect the relative sensitivities or site factors of the methyl and the various methylene groups. 40,41 In practice this means that relatively large effects are observed for the methyl signals:30 ca. 3 times larger than for methylene carbon signals.…”

Section: Discussionmentioning

confidence: 99%

Carbon-13 nuclear magnetic resonance study of mixed micelles. Variation of interchain distances and conformational equilibriums

Weerd¹,

Haan²,

Ven³

et al. 1982

J. Phys. Chem.

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Observed 13C NMR chemical shift changes with respect to their single micelles upon mixed-micelle formation of potassium dodecanoate and short-chain potassium carboxylates (hexanoate up to an including decanoate) are described in all but one case to increasing distances between the apolar ends of the long amphiphile chains as compared with its single micelle. Only for dodecanoate-hexanoate micellar systems can a different conformational equilibrium of the dodecanoate chain not be excluded. Furthermore, recently observed solvent effects upon mixing of n-alkanes of different chain lengths are compared with both the decanoate and nonanoate chemical shift changes upon mixing with the dodecanoate amphiphiles. This leads to the conclusion that the former detergents are mainly subject to increased intermolecular chain packing. Observed effects for the octanoate and heptanoate are not as pronounced, and these surfactants should be considered as borderline cases, while the hexanoate undergoes conformational changes toward more extended forms. Finally, it is observed that maximally ca. 1 equiv of hexanoate or ca. 2 equiv of heptanoate can be incorporated into micelles of potassium dodecanoate. At higher percentages of short-chain surfactants, these maximally incorporated mixed micelles coexist with short-chain monomers up to the concentration where the free short surfactants reach their critical micelle concentration and may form micelles. We postulate that a statistical distribution of dodecanoate molecules in short-chain micelles is attained.

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“…Assuming that P( V^('"j -Vfi'y) is negligible, where V®1" is the corresponding volume term, we have H*(m ~m -Km -= Km ~K» (52) where Ea and Ea,0°a re respectively the corresponding partial molar and partial molar excess configurational energies. 13 The total configurational energy of the mixture (Em), which stems from the attractive interactions (u;i;), is Em/RT = Z KiWij/kT) (53) j»i where i, j = 1, 2, 3, 4 and the A/;/s are given by eq [3][4][5][6][7][8][9][10][11][12] and 28-31.25 Therefore…”

Section: Glc Equationsmentioning

confidence: 99%

Lattice model for nonrandom pairing and the determination of "sociation" constants of organic complexes

Martire¹

1983

J. Phys. Chem.

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2425Flgure 4. Transmission electron micrograph of R/TiO, X434 000.scope grids, showed that samples 1 and 3 were SMSI and sample 2 was not.The morphology of Pt crystallites observed in Pt/TiO, (H, pretreated) sample (an SMSI material) is close to polyhedral (Figure 1). The Pt particle size ranges from 30 to 280 A. The transmission electron micrograph of the support, TiO, (H2 pretreated), is shown in Figure 2. The surface of the support is quite smooth and no small, local, particle-like features are observed. As compared to the reduced sample, Figure 1, the morphology of Pt crystallites in the oxidized Pt/TiO, (H2 pretreated) sample showing no SMSI character is more hemispherical as shown in Figure 3. Those circled Pt crystallites, about 100 A in diameter (Figure 3a), are much more like hemispheres than polyhedra as compared to those of about the same size shown in Figure 1. The crystallites with diameters less than 100 A also appear hemispherical (Figure 3b) although the photograph does not provide as clear a view as Figure 1. The morphology of Pt in the Pt/TiO sample is assigned as "raftlike" based on the flat shape of the darker areas shown in the TEM micrograph of Figure 4. XPS datalo also supports a raftlike morphology assignment for Ptsupported on TiO. While the surface atomic ratios of O/Ti for all the samples are all about the same (3.2 f 0.2), the Pt/Ti ratios are quite different. The values are 0.10 for Pt/Ti02 (H2 pretreated) or oxidized Pt/TiO, (H2 pretreated) and 0.36 for Pt/TiO. This relatively high value for the Pt/Ti ratio for Pt/TiO is consistent with the TEM results suggesting that Pt supported on T i 0 is more highly dispersed. Since the surfaces of all the sample catalysts are covered by at least 30 A thick TiO, layers, as revealed by our XPS study,1° the morphology variations observed in this study are better understood by considering interactions of Pt with the bulk or subsurface of the supports instead of local interfacial metal-metal bond formation. As shown by XRD measurements,1° H2 reduction at 875 "C for TiO, generates a subsurface layer of Ti901,. The bulk becomes more conductive and can be characterized as Ti02 with a considerable number of anion vacancies. Our bulk reduction model consistently accounts for the observed SMSI effect in Pt/Ti02 (H2 pretreated) and Pt/TiO systems and the observed morphology variations in these two systems, as compared to oxidized Pt/Ti02 (H, pretreated) system with no SMSI property, in the following way. According to the proposed model, the bulk conduction band electrons tunnel readily from the Ti9Ol7 subsurface layer of prereduced TiO, support through a thin layer of reoxidized TiO, at the surface to reach the supported Pt particles where they are trapped and furnish negatively charged particles.These unstable charged Pt crystallites tend to change their morphology in order to reduce the local electrostatic potential. This occurs by increasing the Pt surface area (i.e., changing from the hemispherical to polyhedral to raftlike as the charge increases).Ack...

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Effet de solvant en résonance magnétique nucléaire de ¹³C. I. Cas d'un soluté apolaire: n-pentane

Cited by 28 publications

References 8 publications

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

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

Carbon-13 nuclear magnetic resonance study of mixed micelles. Variation of interchain distances and conformational equilibriums

Lattice model for nonrandom pairing and the determination of "sociation" constants of organic complexes

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Effet de solvant en résonance magnétique nucléaire de 13C. I. Cas d'un soluté apolaire: n-pentane

Cited by 28 publications

References 8 publications

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

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

Carbon-13 nuclear magnetic resonance study of mixed micelles. Variation of interchain distances and conformational equilibriums

Lattice model for nonrandom pairing and the determination of "sociation" constants of organic complexes

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Effet de solvant en résonance magnétique nucléaire de ¹³C. I. Cas d'un soluté apolaire: n-pentane

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

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