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DFT/B3LYP Study of the O–H Bond Dissociation Enthalpies and Proton Affinities of para- and meta-Substituted Phenols in Water and Benzene
Klein, Erik, Rimarčík, Ján and Lukeš, Vladimír DFT/B3LYP Study of the O–H Bond Dissociation Enthalpies and Proton Affinities of para- and meta-Substituted Phenols in Water and Benzene Acta Chimica Slovaca, Vol.2, No. 2, 2009, 37-51
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| Attached Files |
| Name |
Description |
MIMEType |
Size |
Downloads |
acs_0045.pdf
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acs_0045.pdf |
application/pdf |
136.47KB |
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| Author(s) |
Klein, Erik
Rimarčík, Ján
Lukeš, Vladimír
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| Title |
DFT/B3LYP Study of the O–H Bond Dissociation Enthalpies and Proton Affinities of para- and meta-Substituted Phenols in Water and Benzene
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| Journal name |
Acta Chimica Slovaca
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| Publication date |
2009
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| Year available |
2009
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| Volume number |
2
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| Issue number |
2
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| ISSN |
1337-978X
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| Start page |
37
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| End page |
51
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| Total pages |
15
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| Place of publication |
Bratislava
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| Publisher |
Slovak Technical University
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| Collection year |
2009
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| Language |
english
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| Subject |
250000 Chemical Sciences
250100 Physical Chemistry (incl. Structural)
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| Abstract/Summary |
For 30 para- and meta-substituted phenols in two solvents – water and benzene, the reaction enthalpies related to two mechanisms of phenolic antioxidants action, hydrogen atom transfer (HAT) and sequential proton loss electron transfer (SPLET), were calculated using IEF-PCM DFT/B3LYP/6-311++G** method. Phenolic O–H bond dissociation enthalpy (BDE) represents the reaction enthalpy of HAT. Phenoxide anion (ArO–) proton affinity (PA) is related to the first step of SPLET – abstraction of proton from the phenol molecule. Except the comparison of calculated BDEs with available experimental and/or theoretical values, obtained BDEs and PAs were correlated with Hammett constants. We have found that electron-withdrawing groups increase BDE, while electron-donating substituents cause a rise in PA. On the contrary, electron-donating groups lower BDE and induce the increase in PA. Dependences of BDE and PA values on Hammett constants of the substituents are linear. From the thermodynamic point of view, entering SPLET mechanism represents the most probable process in water, where PAs of all studied phenols are considerably lower than BDEs. However, in benzene, BDEs are lower than PAs, i.e. HAT represents the most probable pathway. The only exception is p-nitrophenol – its PA is lower than BDE. In comparison to gas-phase, studied solvents attenuate the substituent effect on PA. On the other hand, substituent induced changes in BDE are larger in the solution-phase.
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| Keyword(s) |
integral equation formalism polarizable continuum model
phenolic antioxidant
salvation
solvent effect
substituent effect
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