Trimeric Association of <i>t</i>-Butanol by NMR

Saunders, Martin; Hyne, J. B.

doi:10.1063/1.1744453

Cited by 36 publications

(10 citation statements)

References 4 publications

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“…The chemical shifts of the OH proton in both the monomer and clusters referenced to the averaged value of the magnetic shielding constants of methyl protons in the methanol monomer are shown in Figure . In Figure , the chemical shift of the OH proton of monomer δ monomer is −3.15 ppm, which is a value similar to the −3.3 to −3.45 ppm referenced to the methyl proton in the recent NMR studies. ,, The experimental chemical shift difference between the OH proton of the monomer and of the cluster is −4.70 ppm for the tetramer, which is close to the corresponding calculated values of −5.10 (−5.18) ppm for the cyclic (chain) tetramer. However, it is different from those of −3.71 (−3.92) ppm for the cyclic (chain) trimer and −5.58 (−5.37) ppm for the cyclic (chain) pentamer.…”

Section: Resultssupporting

confidence: 83%

Ab Initio Study of Proton Chemical Shift in Supercritical Methanol Using Gas-Phase Approximation

2001

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Chemical shifts of the OH proton in supercritical methanol referenced to the methyl proton of methanol monomer have been estimated theoretically using the ab initio molecular orbital (MO) method. The degree of dissociation from hydrogen-bonded methanol clusters to monomers calculated using the CCSD(T)/6-31+G(d)//MP2(frozen-core)/6-31+G(d) level of theory indicates that supercritical methanol is comprised of 89% monomer and 10% cyclic tetramer plus ∼1% dimer at the critical point (T c = 512.6 K; P c = 8.09 MPa). The predominant existence of the cyclic tetramers rather than the dimers in supercritical methanol is in contrast to previous theoretical results for supercritical water that indicate the composition of, except for 80% monomer, 20% dimer with little existence of a larger size of clusters at the critical point (T c = 647.1 K; P c = 22.06 MPa). It is also found that a significant fluctuation of the composition of methanol should be caused by a greater change in the degree of dissociation of the cyclic tetramer near the critical point. On the basis of the above supercritical methanol composition, the chemical shift of the OH proton is determined to be −2.00 ppm at the MP2(frozen-core)/6-31+G(d)//MP2(frozen-core)/6-31+G(d) level of theory, which excellently reproduces the recent NMR experimental results.

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Section: Resultssupporting

confidence: 83%

Ab Initio Study of Proton Chemical Shift in Supercritical Methanol Using Gas-Phase Approximation

2001

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“…The self-association of alcohols is more complicated involving both closed cyclic and open polymeric aggregates (Figure c). − A study of the interaction of alcohols with pyridine N-oxide in cyclohexane suggested that alcohol aggregates interact more strongly with solutes than the corresponding monomers . We measured the stability of the H-bonded complex formed by perfluoro- t -butyl alcohol and tri- n -butylphosphine oxide in 13 different solvents.…”

Section: Introductionmentioning

confidence: 99%

Interplay of Self-Association and Solvation in Polar Liquids

et al. 2013

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The association constants for formation a 1:1 complex between 4-phenyl azophenol and tri-n-butylphosphine oxide were measured in mixtures of n-octane and n-decanol, n-octane and n-hexanoic acid, and n-octane and 2-ethylhexyl acetamide. The experiments provide insight into the competition between solvent self-association and solvent-solute interactions in these systems. The solvation properties of the three polar solvents are quite different from one another and from polar solvents that do not self-associate. Carboxylic acids form dimers in concentrated solution (>1 mM in alkanes). Carboxylic acid dimers have exposed H-bond acceptor sites that solvate H-bond donor solutes with a similar binding affinity to carboxylic acid monomers. The carboxylic acid H-bond donor site is inaccessible in the dimer and is not available to solvate H-bond acceptor solutes. The result is that solvation of H-bond acceptor solutes is in competition with solvent dimerization, whereas solvation of H-bond donor solutes is not. Secondary amides form linear polymers in concentrated solution (>10 mM in alkanes). The solvation properties of the secondary amide aggregates are similar to those of carboxylic acid dimers. Solvation of H-bond acceptor solutes must compete with solvent self-association, because the amide H-bond donor site is not accessible in the middle of a polymeric aggregate. However, the amide aggregates have exposed H-bond acceptor sites, which solvate H-bond donor solutes with similar binding affinity to amide monomers. Alcohols form cyclic tetramers at concentrations of 100 mM in alkanes, and these cyclic aggregates are in equilibrium with linear polymeric aggregates at concentrations above 1 M. The alcohol aggregates have exposed H-bond acceptor sites that solvate H-bond donor solutes with similar binding affinity to alcohol monomers. Although the alcohol H-bond donor sites are involved in H-bond interactions with other alcohols in the aggregates, these sites are sufficiently exposed to form a second bifurcated H-bond with H-bond acceptor solutes, and these interactions have a similar binding affinity to alcohol monomers. The result is that self-association of alcohols does not compete with solvation of solutes, and alcohols are significantly more polar solvents than expected based on the properties of alcohol monomers.

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“…Workers on n.m.r. interpreted their data (22) on the basis of a far simpler model consisting of a single equilibrium between monomer and multimer, all other multimers being neglected. The change in chemical shift was calculated for a monomer-dimer equilibrium, then monomer-trimer, and finally monomer-tetramer.…”

Section: Further Discussion Of Resultsmentioning

confidence: 99%

Dielectric Studies. Part XXXI. Analysis of the Dielectric Data of Phenol and its Polymerized Forms

Magee¹,

Walker²

1971

Can. J. Chem.

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The dielectric absorption and dispersions of several solutions of phenol inp-xylene have been measured at four microwave frequencies and at 2 MHz at a temperature of 25 "C. The data have been analyzed in terms of a mean relaxation time, a distribution parameter, and an apparent dipole moment which are useful empirical parameters for assessing the state of aggregation of the phenol molecules. The relaxation time at the lowest practicable concei~tration (0.02 mole fraction) is long for a molecule expected to relax predominantly by an intramolecular process. This and the behavior of the relaxation time and apparent dipole moment with increasing concentration are considered in terms of a model based on progressive association into an extended series of multimers, the trimer having a zero (or low) dipole moment and higher multimers becoming increasingly flexible.On a mesure I'absorption et la dispersion diklectrique de solutions de phCnol dans le para-xylene a quatre frequences microonde ainsi qu'a 2 MHz, a 25 "C. Les risultats ont CtC analyses en termes d'un temps de relaxation moyen, d'un parametre de distribution ainsi que d'un moment dipolaire apparent qui sont des parametres empiriques utiles pour caracteriser 1'Ctat d'aggrkgation des molecules de phenol.Le temps de relaxation a la concentration la plus faible a laquelle il a Cte possible de le mesurer (0.02 en fraction molaire), est grand pour une molecule dont le processus de relaxation serait a prkdominance intramolCculaire. Ce fait ainsi que la variation du temps de relaxation et du moment dipolaire apparent avec la concentration ont e t t interprCtCs en termes d'un modele base sur une association progressive en un nombre de plus en plus grand de multimeres, le trimere possCdant un moment dipolaire nu1 (ou faible) et les multimeres d'ordre supCrieur Btant progressivement de plus en plus flexibles.Canadian Journal of Chemistry, 49, 1106Chemistry, 49, (1971 Introduction Association of phenol in solutions has been studied by several physical methods (1) notable among which are infrared, nuclear magnetic resonance (n.m.r.), and polarization measurements. Fischer (2) has employed radiofrequency measurements to study the relationship between dielectric relaxation and self-association of phenols in carbon tetrachloride, while Aihara and Manse1 Davies (3) considered some aspects of association in a more general study. More recently Garg and Smyth (4) have studied alcohols at microwave and lower frequencies. Malecki and Doperala (5) have also shown how dielectric polarization yields much information on the association of alcohols. However, detailed microwave investigations of the dielectric relaxation of phenol in solution with a view to obtaining more data on self-association seem to be lacking although this technique yields relaxation times, distribution coefficients, and dipole moments, each of which might be sensitive to the interactions. Our publications (6,7) on dilute solutions of phenols have not been primarily concerned with association.

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Trimeric Association of t-Butanol by NMR

Cited by 36 publications

References 4 publications

Ab Initio Study of Proton Chemical Shift in Supercritical Methanol Using Gas-Phase Approximation

Ab Initio Study of Proton Chemical Shift in Supercritical Methanol Using Gas-Phase Approximation

Interplay of Self-Association and Solvation in Polar Liquids

Dielectric Studies. Part XXXI. Analysis of the Dielectric Data of Phenol and its Polymerized Forms

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