Are calculated enthalpies of formation sometimes more reliable than experimental? A test on alkyl substituted benzoic acids

Kód výsledku v IS VaVaI

RIV/60461373:22310/06:00017572 - isvavai.cz

Nalezeny alternativní kódy

RIV/61388963:_____/06:00041087

Výsledek na webu

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DOI - Digital Object Identifier

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Jazyk výsledku

angličtina

Název v původním jazyce

Are calculated enthalpies of formation sometimes more reliable than experimental? A test on alkyl substituted benzoic acids

Popis výsledku v původním jazyce

Energies of 20 alkyl-substituted benzoic acids were calculated at the levels B3LYP/6-311+G(d,p)//B3LYP/6-311+G(d,p) and MP2/6-311+G(d,p)//MP2/6-311+G(d,p); the pertinent enthalpies at 298 K were calculated at the same levels. Comparison with experimentalenthalpies of formation fH°g(298) was carried out in terms of isodesmic reactions, that is, in the relative values. Of the four calculated quantities, the DFT enthalpies yielded best correlation with the standard deviation of 2.1 kJ mol-1, near to the experimental uncertainty; the DFT energies are only slightly worse and the MP2 enthalpies or energies much worse. However, the DFT method overestimated systematically the substituent effects and had to be calibrated. Comparison with the experimental gas-phase acidities was less telling and the fit was worse because both methods overestimated the substituent effects. Extending the base in selected examples did not give better results. Although the systematic deviations are evidently due to

Název v anglickém jazyce

Are calculated enthalpies of formation sometimes more reliable than experimental? A test on alkyl substituted benzoic acids

Popis výsledku anglicky

Energies of 20 alkyl-substituted benzoic acids were calculated at the levels B3LYP/6-311+G(d,p)//B3LYP/6-311+G(d,p) and MP2/6-311+G(d,p)//MP2/6-311+G(d,p); the pertinent enthalpies at 298 K were calculated at the same levels. Comparison with experimentalenthalpies of formation fH°g(298) was carried out in terms of isodesmic reactions, that is, in the relative values. Of the four calculated quantities, the DFT enthalpies yielded best correlation with the standard deviation of 2.1 kJ mol-1, near to the experimental uncertainty; the DFT energies are only slightly worse and the MP2 enthalpies or energies much worse. However, the DFT method overestimated systematically the substituent effects and had to be calibrated. Comparison with the experimental gas-phase acidities was less telling and the fit was worse because both methods overestimated the substituent effects. Extending the base in selected examples did not give better results. Although the systematic deviations are evidently due to

Druh

J_x - Nezařazeno - Článek v odborném periodiku (Jimp, Jsc a Jost)

CEP obor

CC - Organická chemie

OECD FORD obor

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Projekt

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Návaznosti

Z - Vyzkumny zamer (s odkazem do CEZ)

Rok uplatnění

2006

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Název periodika

Journal Comput.Chem.

ISSN

0192-8651

e-ISSN

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Svazek periodika

27

Číslo periodika v rámci svazku

5

Stát vydavatele periodika

GB - Spojené království Velké Británie a Severního Irska

Počet stran výsledku

8

Strana od-do

571-577

Kód UT WoS článku

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EID výsledku v databázi Scopus

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