Further consideration of the gas–liquid chromatographic method for determining the intramolecular hydrogen bond energies with the example of 2-substituted phenols

Skvortsov, Igor M.; Makarov, O. E.; Fedorov, Evgenii E.

doi:10.1016/j.chroma.2006.07.057

Cited by 8 publications

(6 citation statements)

References 33 publications

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“…We performed the deconvolution of the overlapping bands and calculated the integrated intensity of the individual curves in order to determine R values (see Table 11 The strength of the intermolecular HB of 2-methoxyphenol with proton acceptors can not be determined directly because O-H group is involved in the formation of intramolecular HB. In the literature, 5,8,9,11 values of intermolecular H-bond enthalpy of ortho-isomer are suggested to be equal to the enthalpies of HB formation of the para-isomer. Confirmation of equal strength of HBs for 2-and 4-methoxyphenols with proton acceptors was also found in our work by analyzing the absorption frequencies of the complexes (see Table 10).…”

Section: Thermochemistry: Strength Of Intramolecular Hb In Ortho-meth...mentioning

confidence: 99%

“…The strength of the intra-HB in 2-methoxyphenol has been extensively investigated using IR spectroscopy, − , gas chromatography, calorimetry, , and quantum-chemical methods ,− with considerable spread of values within 2.7−33 kJ·mol −1 . Modern first-principles calculations, based on the use of the “ cis−trans ” method, predict the strength of the intra-HB in 2-methoxyphenol on the level of 16−19 kJ·mol −1 .…”

Section: Introductionmentioning

confidence: 99%

“…[3][4][5][6][7] Consequently, practically all the molecules of 2-methoxyphenol in a solution form intramolecular HBs. [3][4][5][6][7] The strength of the intra-HB in 2-methoxyphenol has been extensively investigated using IR spectroscopy, [3][4][5]8 gas chromatography, 9 calorimetry, 10,11 and quantum-chemical methods 7,[12][13][14][15][16][17][18][19] with considerable spread of values within 2.7-33 kJ • mol -1 . Modern first-principles calculations, based on the use of the "cis-trans" method, predict the strength of the intra-HB in 2-methoxyphenol on the level of 16-19 kJ • mol -1 .…”

Section: Introductionmentioning

confidence: 99%

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Pairwise Substitution Effects, Inter- and Intramolecular Hydrogen Bonds in Methoxyphenols and Dimethoxybenzenes. Thermochemistry, Calorimetry, and First-Principles Calculations

Varfolomeev

Abaidullina²,

Solomonov³

et al. 2010

J. Phys. Chem. B

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Methoxyphenols are the structural fragments of different antioxidants and biologically active molecules, which are able to form strong intermolecular and intramolecular hydrogen bonds in condensed matter. In the present work, thermochemical, Fourier transform infrared (FTIR)-spectroscopic and quantum-chemical studies of methoxyphenols and its H-bonded complexes in solution and gas phase have been carried out. Thermodynamic properties (standard molar enthalpies of formation, vapor pressure, vaporization enthalpies, sublimation enthalpies, and fusion enthalpies) of 2-methoxyphenol, 3-methoxyphenol, 4-methoxyphenol, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, and 1,4-dimethoxybenzene have been studied in this work. To verify the experimental data, ab initio calculations of all compounds have been performed using density functional theory (DFT), MP2, and G3 methods. The quantitative analysis of ortho, meta, and para pairwise-substituent effects in methoxyphenols has been performed. Solution enthalpies of methoxyphenols at infinite dilution in proton acceptor solvents have been measured. Calorimetric data shows that intermolecular hydrogen bond strength in complexes of 2-methoxyphenol with organic bases is less than that for 4-methoxyphenol. Two experimental approaches for determination of enthalpy of intramolecular hydrogen bonds in ortho-methoxyphenols were proposed. The new results help to resolve uncertainties in the available thermochemical data on methoxyphenols and dimethoxybenzenes and to realize relations among properties and structures for these compounds.

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Section: Thermochemistry: Strength Of Intramolecular Hb In Ortho-meth...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Pairwise Substitution Effects, Inter- and Intramolecular Hydrogen Bonds in Methoxyphenols and Dimethoxybenzenes. Thermochemistry, Calorimetry, and First-Principles Calculations

Varfolomeev

Abaidullina²,

Solomonov³

et al. 2010

J. Phys. Chem. B

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“…The strength of this bond HB intra = (À6.5 AE 0.2) kJ mol À1 was determined from the temperature dependence of the OH-stretching vibration frequency shifts. 60 However, this result is markedly low compared to the HB intra E À30 kJ mol À1 derived with the gas-liquid chromatography (GLC) [61][62][63] and the HB intra = À51.0 kJ mol À1 calculated with the B3LYP/6-31G(d,p). 64 A compilation of the data available in the literature on the strength of the intra-molecular HB for methyl 2-hydroxybenzoate in the gas phase is given in Table 6.…”

Section: Strength Of Intra-molecular Hydrogen Bonding In Alkyl 2-hydr...mentioning

confidence: 82%

“…The GLC method [61][62][63] determines the intra-HB energy as the difference between the heats of dissolution (in a polar stationary liquid phase) of two isomers, one with intra-HB and the other not (e.g. methyl 2-hydroxybenzoate and methyl 4-hydroxybenzoate).…”

Section: Strength Of Intra-molecular Hydrogen Bonding In Alkyl 2-hydr...mentioning

confidence: 99%

Experimental and computational thermochemistry: how strong is the intramolecular hydrogen bond in alkyl 2-hydroxybenzoates (salicylates)

Verevkin¹,

Portnova²,

Emel´yanenko³

et al. 2023

Phys. Chem. Chem. Phys.

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Hydrogen‐Atom Transfer Reactions from ortho‐Alkoxy‐Substituted Phenols: An Experimental Approach

Amorati

Menichetti²,

Mileo

et al. 2009

Chemistry A European J

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The role of intramolecular hydrogen bonding (HB) on the bond-dissociation enthalpy (BDE) of the phenolic O-H and on the kinetics of H-atom transfer to peroxyl radicals (k(inh)) of several 2-alkoxyphenols was experimentally quantified by the EPR equilibration technique and by inhibited autoxidation studies. These compounds can be regarded as useful models for studying the H-atom abstraction from 2-OR phenols, such as many lignans, reduced coenzyme Q and curcumin. The effects of the various substituents on the BDE(O-H) of 2-methoxy, 2-methoxy-4-methyl, 2,4-dimethoxyphenols versus phenol were measured in benzene solution as -1.8; -3.7; -5.4 kcal mol(-1), respectively. In the case of polymethoxyphenols, significant deviations from the BDE(O-H) values predicted by the additive effects of the substituents were found. The logarithms of the k(inh) constants in cumene were inversely related to the BDE(O-H) values, obeying a linear Evans-Polanyi plot with the same slope of other substituted phenols and a y-axis intercept slightly smaller than that of 2,6-dimethyl phenols. In the cases of phenols having the 2-OR substituent included in a five-membered condensed ring (i.e, compounds 9-11), both conformational isomers in which the OH group points toward or away from the oxygen in position 2 were detected by FTIR spectroscopy and the intramolecular HB strength was thus estimated. The contribution to the BDE(O-H) of the ortho-OR substituent in 9, corrected for intramolecular HB formation, was calculated as -5.6 kcal mol(-1). The similar behaviour of cyclic and non-cyclic ortho-alkoxy derivatives clearly showed that the preferred conformation of the OMe group in ortho-methoxyphenoxyl radicals is that in which the methyl group points away from the phenoxyl oxygen, in contrast to the geometries predicted by DFT calculations.

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Further consideration of the gas–liquid chromatographic method for determining the intramolecular hydrogen bond energies with the example of 2-substituted phenols

Cited by 8 publications

References 33 publications

Pairwise Substitution Effects, Inter- and Intramolecular Hydrogen Bonds in Methoxyphenols and Dimethoxybenzenes. Thermochemistry, Calorimetry, and First-Principles Calculations

Pairwise Substitution Effects, Inter- and Intramolecular Hydrogen Bonds in Methoxyphenols and Dimethoxybenzenes. Thermochemistry, Calorimetry, and First-Principles Calculations

Experimental and computational thermochemistry: how strong is the intramolecular hydrogen bond in alkyl 2-hydroxybenzoates (salicylates)

Hydrogen‐Atom Transfer Reactions from ortho‐Alkoxy‐Substituted Phenols: An Experimental Approach

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