Substituent effects on the acidity of weak acids. 3. Phenols and benzyl alcohols

Journal of Organic Chemistry

Volumn 68, Issue 3, 2003, Pages 875-882

  Wiberg, Kenneth B ^a  

^a YALE UNIVERSITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

SUBSTITUENT EFFECTS;

ACIDITY; ALCOHOLS; BENZENE; NEGATIVE IONS; OXYGEN;

PHENOLS;

BENZOIC ACID DERIVATIVE; BENZYL ALCOHOL; CARBOXYLIC ACID DERIVATIVE; PHENOL DERIVATIVE;

AB INITIO CALCULATION; ACIDITY; ARTICLE; CALCULATION; CHEMICAL REACTION; ELECTRON; GAS;

EID: 0037423262     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo020560b     Document Type: Article

References (23)

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3. For previous studies of substituent effects on phenols, see: Fujio, M.; McIver, R. T., Jr.; Taft, R. W. J. Am. Chem. Soc. 1981, 103, 4017.
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6. B3LYP calculations are known to give good calculated vibrational frequencies: Koch, W.; Holthausen, M. C. A Chemist's Guide to Density Functional Theory, 2nd ed.; Wiley-VCH: Weinheim, Germany, 2001.
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10. The structures and energies are shown in Table S1 of the Supporting Information.
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13. NIST Chemistry Webbook (www.nist.gov). The proton affinity data were compiled by E. P. Hunter and S. G. Lias, and the negative ion energetics data were compiled by J. H. Bartmess.
14. 3 where very low calculated frequencies were found, leading to unreliable free energy terms, the other para substituents and all of the meta-substituents gave TΔS = 7.5 ± 0.1 kcal/mol. A more detailed calculation would require additional information on the rotational potential energy terms for the C-O and C-X bonds, and calculations of the rotational energy levels. In view of the uncertainty in the experimental data, the additional effort did not appear to be warranted.
15. The estimated uncertainty between pairs of acids that are directly compared is ±0.2 kcal/mol (ref 3). For acidities derived from a ladder of comparisons, the uncertainty will be larger and ±0.5 kcal/mol would appear to be a reasonable estimate.
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21. Prof. John Bartmess, private communication.
22. 3 groups, the conformation used in the calculations had a plane of symmetry containing the benzene ring. This is in some cases not the preferred conformation, but since they have a 6-fold rotational barrier, the differences in energy are negligible.
23. Wiberg, K. B.; Breneman, C. M. J. Am. Chem. Soc. 1990, 112, 8765.