Solvent effects on the tautomeric equilibrium of 2,4-pentanedione

Spencer, J. N.; Holmboe, Eric S.; Kirshenbaum, M. R.; Firth, D. W.; Pinto, Patricia B.

doi:10.1139/v82-174

Cited by 88 publications

(60 citation statements)

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“…Nitrogen compounds are known to form weak electron donor-acceptor complexes with the polyhalogenated molecules, [76][77][78][79] which are now called halogen-bonded complexes. [80,81] As a first approximation, we have modelled this interaction by the association of one solvent molecule halogen-bonded to one or more nitrogen atoms.…”

Section: Piperidine Conformermentioning

confidence: 99%

A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

Besseau

Graton

Berthelot

2008

Chemistry A European J

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The experimental pKHB hydrogen-bond (HB) basicity scale and the corresponding DeltaH[symbol: see text]HB enthalpic scale of nitrogen compounds are extended and analysed in light of simple theoretical descriptors using the B3LYP density functional method and a medium-size basis set (6-31+G(d,p)).The selected training set includes 59 monofunctional unhindered nitrogen bases for which homogeneous and accurate experimental pKHB and DeltaH[symbol: see text]HB data have been determined by means of the association equilibrium of the bases with a reference hydrogen-bond acid, 4-fluorophenol, in CCl4. The three hybridisation states encountered in the nitrogen atom, sp, sp2 and sp3, are equally represented in this data set. A proper estimation of their experimental enthalpy (DeltaH[symbol: see text]HB) is directly attainable from the theoretical enthalpy of the complexation reaction with hydrogen fluoride (DeltaH[symbol: see text](HF)). However, a second parameter is required to calculate with good accuracy the experimental free energy of association represented by pKHB. About 99% of the variance of the pKHB scale is described by a bilinear equation using the minimum electrostatic potential (Vs,min) of the monomer in addition to the interaction energy (D0(HF). The equations are tested for an external set of 99 additional compounds including very different nitrogen bases such as ortho-substituted pyridines, polyazines and azoles.Theoretical calculations give a reliable estimation of hydrogen-bond basicity provided that the populations of the different isomers of the bases are taken into account by using the Boltzmann law, and that a specific halogen-bond interaction with the solvent CCl4 is considered for polybasic molecules.The pKHB scale can thus be extended to important classes of species experimentally inaccessible in CCl4, to polynitrogen compounds and to molecules of biological significance.

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Section: Piperidine Conformermentioning

confidence: 99%

A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

Besseau

Graton

Berthelot

2008

Chemistry A European J

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“…13,[16][17][18][19][20][21][22][23][24][25][26][27][28] Both spectroscopic and chemical methods have been used to determine the enthalpy of tautomerization in the gas phase. Unlike the condensed phase studies, agreement between methods is less than satisfactory.…”

Section: Introductionmentioning

confidence: 99%

The Thermochemistry of 2,4-Pentanedione Revisited: Observance of a Nonzero Enthalpy of Mixing between Tautomers and Its Effects on Enthalpies of Formation

et al. 2005

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The enthalpies of formation of pure liquid and gas-phase (Z)-4-hydroxy-3-penten-2-one and 2,4-pentanedione are examined in the light of some more recent NMR studies on the enthalpy differences between gas-phase enthalpies of the two tautomers. Correlation gas chromatography experiments are used to evaluate the vaporization enthalpies of the pure tautomers. Values of (51.2 ( 2.2) and (50.8 ( 0.6) kJ‚mol -1 are measured for pure 2,4-pentanedione and (Z)-4-hydroxy-3-penten-2-one, respectively. The value of (50.8 ( 0.6) kJ‚mol -1 can be contrasted to a value of (43.2 ( 0.2) kJ‚mol -1 calculated for pure (Z)-4-hydroxy-3-penten-2-one when the vaporization enthalpy is measured in a mixture of tautomers. The difference is attributed to an endothermic enthalpy of mixing that destabilizes the mixture relative to the pure components. Calculation of new enthalpies of formation for (Z)-3-hydroxy-3-penten-2-one and 2,4-pentanedione in both the gas, ∆ f H°m(g) ) (-378.2 ( 1.2) and (-358.9 ( 2.5) kJ‚mol -1 , respectively, and liquid phases, ∆ f H°m(l) ) (-429.0 ( 1.0) and (-410.1 ( 1.2) kJ‚mol -1 , respectively, results in enthalpy differences between the two tautomers both in the liquid and gas phases that are identical within experimental error, and in excellent agreement with recent gas-phase NMR studies.

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“…Molar volume difference (MV(to1uene) -MV(benzene) = 17.4 mL/mol) does not appear to significantly influence eq. [6], because the inclusion of a term in SH (Hildebrand solubility parameter) (9), which provides a measure of the energy of cavity formation (lo), does not improve the equation. The poor correlation coefficient is due largely to the nearly horizontal slope (small s value) (1 I).…”

Section: Toluene and Mesitylenementioning

confidence: 99%

Enthalpies of interaction of aromatic solutes with organic solvents

Stephenson¹,

Fuchs²

1985

Can. J. Chem.

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Heats of solution of several aromatic solutes (benzene, toluene, mesitylene, nitrobenzene, α,α,α-trifluorotoluene, anisole) and model compounds (n-butyl methyl ether, cyclohexane) in 17 organic solvents (n-heptane, cyclohexane, carbon tetrachloride, 1,2-dichloroethane, α,α,α-trifluorotoluene, triethylamine, butyl ether, ethyl acetate, dimethylformamide, dimethyl sulfoxide, benzene, toluene, mesitylene, t-butyl alcohol, 1-octanol, methanol, 2,2,2-trifluoroethanol) have been combined with solute heats of vaporization to give enthalpies of transfer from vapor to solvent (ΔH(v → S)). Differences between solute and model values (ΔΔH(v → S) = ΔH(v → S) (aromatic solute)–ΔH(v → S) (model) were used to evaluate aromatic solute–solvent polar interactions. Correlations of ΔΔH(v → S) with solvent dipolarity–polarizability (Taft–Kamlet π* parameter) have been determined.

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Solvent effects on the tautomeric equilibrium of 2,4-pentanedione

Cited by 88 publications

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A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

The Thermochemistry of 2,4-Pentanedione Revisited: Observance of a Nonzero Enthalpy of Mixing between Tautomers and Its Effects on Enthalpies of Formation

Enthalpies of interaction of aromatic solutes with organic solvents

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Solvent effects on the tautomeric equilibrium of 2,4-pentanedione

Cited by 88 publications

References 0 publications

A Theoretical Evaluation of the pKHBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

A Theoretical Evaluation of the pKHBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

The Thermochemistry of 2,4-Pentanedione Revisited: Observance of a Nonzero Enthalpy of Mixing between Tautomers and Its Effects on Enthalpies of Formation

Enthalpies of interaction of aromatic solutes with organic solvents

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A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases

A Theoretical Evaluation of the pK_HBand Δ$H{{{\,\ominus}\hfill \atop {\rm HB}\hfill}}}$ Hydrogen‐Bond Scales of Nitrogen Bases