Substituent effects on the electronic structure and pKa benzoic acid

Maxime Guillaume; Edith Botek; Benoît Champagne; Frédéric Castet; Laurent Ducasse

Substituent effects on the electronic structure and pK_a benzoic acid

Maxime Guillaume, Edith Botek, Benoît Champagne, Frédéric Castet, Laurent Ducasse

Unit of theoretical and structural physico-chemistry

Research output: Contribution to journal › Article › peer-review

Abstract

The effects of substituents on the pK_as of a set of 16 substituted benzoic acids have been examined using density functional theory [B3LYP/6-311G(d, p)] calculations. A variety of quantum chemical parameters were examined as indicators for the variations observed in the experimental pK_as, including the Löwdin, Mulliken, AIM, and natural population analysis charges (Q_L, Q_M, Q_A, and Q_n) on atoms of the dissociating carboxylic acid group, the energy difference (ΔE_prot) between the carboxylic acid and its conjugate base, and the Wiberg bond index. Several of these calculated quantities yielded excellent correlations with the experimental pK_a: ΔH_prot, r² = 0.958; Q_L(H), r² = 0.963; Q_n(CO₂H), r² = 0.969; Q_L(CO₂ ^-), r² = 0.970; and Q_L(CO₂H), r² = 0.978. The best correlation observed with the pK_a, as expected, was from, the empirical Hammett constants designed for this purpose (r² = 0.999).

Original language	English
Pages (from-to)	1396-1403
Number of pages	8
Journal	International Journal of Quantum Chemistry
Volume	90
Issue number	4-5
Publication status	Published - 15 Nov 2002

Keywords

Acid dissociation constants (pKs)
Benzoic acids
Hammett constants
Substituent effects

Cite this

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title = "Substituent effects on the electronic structure and pKa benzoic acid",

abstract = "The effects of substituents on the pKas of a set of 16 substituted benzoic acids have been examined using density functional theory [B3LYP/6-311G(d, p)] calculations. A variety of quantum chemical parameters were examined as indicators for the variations observed in the experimental pKas, including the L{\"o}wdin, Mulliken, AIM, and natural population analysis charges (QL, QM, QA, and Qn) on atoms of the dissociating carboxylic acid group, the energy difference (ΔEprot) between the carboxylic acid and its conjugate base, and the Wiberg bond index. Several of these calculated quantities yielded excellent correlations with the experimental pKa: ΔHprot, r2 = 0.958; QL(H), r2 = 0.963; Qn(CO2H), r2 = 0.969; QL(CO2 -), r2 = 0.970; and QL(CO2H), r2 = 0.978. The best correlation observed with the pKa, as expected, was from, the empirical Hammett constants designed for this purpose (r2 = 0.999).",

keywords = "Acid dissociation constants (pKs), Benzoic acids, Hammett constants, Substituent effects",

author = "Maxime Guillaume and Edith Botek and Beno{\^i}t Champagne and Fr{\'e}d{\'e}ric Castet and Laurent Ducasse",

year = "2002",

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day = "15",

language = "English",

volume = "90",

pages = "1396--1403",

journal = "International Journal of Quantum Chemistry",

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TY - JOUR

T1 - Substituent effects on the electronic structure and pKa benzoic acid

AU - Guillaume, Maxime

AU - Botek, Edith

AU - Champagne, Benoît

AU - Castet, Frédéric

AU - Ducasse, Laurent

PY - 2002/11/15

Y1 - 2002/11/15

N2 - The effects of substituents on the pKas of a set of 16 substituted benzoic acids have been examined using density functional theory [B3LYP/6-311G(d, p)] calculations. A variety of quantum chemical parameters were examined as indicators for the variations observed in the experimental pKas, including the Löwdin, Mulliken, AIM, and natural population analysis charges (QL, QM, QA, and Qn) on atoms of the dissociating carboxylic acid group, the energy difference (ΔEprot) between the carboxylic acid and its conjugate base, and the Wiberg bond index. Several of these calculated quantities yielded excellent correlations with the experimental pKa: ΔHprot, r2 = 0.958; QL(H), r2 = 0.963; Qn(CO2H), r2 = 0.969; QL(CO2 -), r2 = 0.970; and QL(CO2H), r2 = 0.978. The best correlation observed with the pKa, as expected, was from, the empirical Hammett constants designed for this purpose (r2 = 0.999).

AB - The effects of substituents on the pKas of a set of 16 substituted benzoic acids have been examined using density functional theory [B3LYP/6-311G(d, p)] calculations. A variety of quantum chemical parameters were examined as indicators for the variations observed in the experimental pKas, including the Löwdin, Mulliken, AIM, and natural population analysis charges (QL, QM, QA, and Qn) on atoms of the dissociating carboxylic acid group, the energy difference (ΔEprot) between the carboxylic acid and its conjugate base, and the Wiberg bond index. Several of these calculated quantities yielded excellent correlations with the experimental pKa: ΔHprot, r2 = 0.958; QL(H), r2 = 0.963; Qn(CO2H), r2 = 0.969; QL(CO2 -), r2 = 0.970; and QL(CO2H), r2 = 0.978. The best correlation observed with the pKa, as expected, was from, the empirical Hammett constants designed for this purpose (r2 = 0.999).

KW - Acid dissociation constants (pKs)

KW - Benzoic acids

KW - Hammett constants

KW - Substituent effects

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M3 - Article

AN - SCOPUS:0037111965

SN - 0020-7608

VL - 90

SP - 1396

EP - 1403

JO - International Journal of Quantum Chemistry

JF - International Journal of Quantum Chemistry

IS - 4-5

ER -

Substituent effects on the electronic structure and pK_a benzoic acid

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Keywords

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