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Issue 9, 2004
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O–H Bond dissociation enthalpies in hydroxyphenols. A time-resolved photoacoustic calorimetry and quantum chemistry study

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Abstract

Time-resolved photoacoustic calorimetry (TR-PAC) was used to investigate the energetics of O–H bonds of phenol, catechol, pyrogallol, and phloroglucinol. Values of −27.1 ± 3.9, −44.1 ± 4.4 and −1.6 ± 3.8 kJ mol−1, respectively, were obtained for the solution-phase (acetonitrile) O–H bond dissociation enthalpies of the last three compounds relative to the O–H bond dissociation enthalpy in phenol, ΔDHosln(ArO–H) = DHosln(ArO–H) − DHosln(PhO–H). A value of 388.7 ± 3.7 kJ mol−1 was determined for the PhO–H bond dissociation enthalpy in acetonitrile. Density functional theory (MPW1PW91/aug-cc-pVDZ) calculations and complete basis set (CBS-4M) calculations were carried out to analyse intramolecular hydrogen bonding and to predict gas-phase O–H bond dissociation enthalpies, DHo(ArO–H). A microsolvation model, based on the DFT calculations, was used to study the differential solvation of the phenols and their radicals in acetonitrile and to bridge solution- and gas-phase data. The results strongly suggest that ΔDHosln(ArO–H) ≈ ΔDHo(ArO–H). Hence, to calculate absolute gas-phase O–H bond dissociation enthalpies in substituted phenols from the corresponding solution-phase values, the solvation enthalpies of the substituted phenols and their radicals are not required.

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Publication details

The article was received on 07 Nov 2003, accepted on 24 Feb 2004 and first published on 25 Mar 2004


Article type: Paper
DOI: 10.1039/B314093H
Citation: Phys. Chem. Chem. Phys., 2004,6, 2109-2118
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    O–H Bond dissociation enthalpies in hydroxyphenols. A time-resolved photoacoustic calorimetry and quantum chemistry study

    C. F. Correia, R. C. Guedes, R. M. Borges dos Santos, B. J. Costa Cabral and J. A. Martinho Simões, Phys. Chem. Chem. Phys., 2004, 6, 2109
    DOI: 10.1039/B314093H

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