羟基苯甲酸及相应羧基苯氧基自由基的能量学。2-羟基苯甲酸中的分子内氢键。
Energetics of hydroxybenzoic acids and of the corresponding carboxyphenoxyl radicals. Intramolecular hydrogen bonding in 2-hydroxybenzoic acid.
作者信息
Pinto Susana S, Diogo Hermínio P, Guedes Rita C, Costa Cabral Benedito J, Minas da Piedade Manuel E, Martinho Simões José A
机构信息
Centro de Química Estrutural, Complexo Interdisciplinar, Instituto Superior Técnico, 1049-001 Lisboa, Portugal.
出版信息
J Phys Chem A. 2005 Oct 27;109(42):9700-8. doi: 10.1021/jp054220g.
The energetics of the phenolic O-H bond in the three hydroxybenzoic acid isomers and of the intramolecular hydrogen O-H- - -O-C bond in 2-hydroxybenzoic acid, 2-OHBA, were investigated by using a combination of experimental and theoretical methods. The standard molar enthalpies of formation of monoclinic 3- and 4-hydroxybenzoic acids, at 298.15 K, were determined as Delta(f)(3-OHBA, cr) = -593.9 +/- 2.0 kJ x mol(-1) and Delta(f)(4-OHBA, cr) = -597.2 +/- 1.4 kJ x mol(-1), by combustion calorimetry. Calvet drop-sublimation calorimetric measurements on monoclinic samples of 2-, 3-, and 4-OHBA, led to the following enthalpy of sublimation values at 298.15 K: Delta(sub)(2-OHBA) = 94.4 +/- 0.4 kJ x mol(-1), Delta(sub)(3-OHBA) = 118.3 +/- 1.1 kJ x mol(-1), and Delta(sub)(4-OHBA) = 117.0 +/- 0.5 kJ x mol(-1). From the obtained Delta(f)(cr) and Delta(sub) values and the previously reported enthalpy of formation of monoclinic 2-OHBA (-591.7 +/- 1.3 kJ x mol(-1)), it was possible to derive Delta(f)(2-OHBA, g) = -497.3 +/- 1.4 kJ x mol(-1), Delta(f)(3-OHBA, g) = -475.6 +/- 2.3 kJ x mol(-1), and Delta(f)(4-OHBA, cr) = -480.2 +/- 1.5 kJ x mol(-1). These values, together with the enthalpies of isodesmic and isogyric gas-phase reactions predicted by density functional theory (B3PW91/aug-cc-pVDZ, MPW1PW91/aug-cc-pVDZ, and MPW1PW91/aug-cc-pVTZ) and the CBS-QMPW1 methods, were used to derive the enthalpies of formation of the gaseous 2-, 3-, and 4-carboxyphenoxyl radicals as (2-HOOCC(6)H(4)O(), g) = -322.5 +/- 3.0 kJ.mol(-1) Delta(f)(3-HOOCC(6)H(4)O(), g) = -310.0 +/- 3.0 kJ x mol(-1), and Delta(f)(4-HOOCC(6)H(4)O(*), g) = -318.2 +/- 3.0 kJ x mol(-1). The O-H bond dissociation enthalpies in 2-OHBA, 3-OHBA, and 4-OHBA were 392.8 +/- 3.3, 383.6 +/- 3.8, and 380.0 +/- 3.4 kJ x mol(-1), respectively. Finally, by using the ortho-para method, it was found that the H- - -O intramolecular hydrogen bond in the 2-carboxyphenoxyl radical is 25.7 kJ x mol(-1), which is ca. 6-9 kJ x mol(-1) above the one estimated in its parent (2-OHBA), viz. 20.2 kJ x mol(-1) (theoretical) or 17.1 +/- 2.1 kJ x mol(-1) (experimental).
采用实验和理论相结合的方法，研究了三种羟基苯甲酸异构体中酚羟基O-H键以及2-羟基苯甲酸（2-OHBA）中分子内氢键O-H---O-C的能量。通过燃烧量热法测定了单斜晶系3-和4-羟基苯甲酸在298.15 K时的标准摩尔生成焓，分别为Δf(3-OHBA, cr) = -593.9 ± 2.0 kJ·mol⁻¹和Δf(4-OHBA, cr) = -597.2 ± 1.4 kJ·mol⁻¹。对2-、3-和4-OHBA单斜晶系样品进行卡尔维特滴升华量热测量，得到298.15 K时的升华焓值如下：Δsub(2-OHBA) = 94.4 ± 0.4 kJ·mol⁻¹，Δsub(3-OHBA) = 118.3 ± 1.1 kJ·mol⁻¹，Δsub(4-OHBA) = 117.0 ± 0.5 kJ·mol⁻¹。根据得到的Δf(cr)和Δsub值以及先前报道的单斜晶系2-OHBA的生成焓（-591.7 ± 1.3 kJ·mol⁻¹），可以得出Δf(2-OHBA, g) = -497.3 ± 1.4 kJ·mol⁻¹，Δf(3-OHBA, g) = -475.6 ± 2.3 kJ·mol⁻¹，Δf(4-OHBA, g) = -480.2 ± 1.5 kJ·mol⁻¹。这些值，连同密度泛函理论（B3PW91/aug-cc-pVDZ、MPW1PW91/aug-cc-pVDZ和MPW1PW91/aug-cc-pVTZ）和CBS-QMPW1方法预测的等键反应和等旋气相反应的焓，用于推导气态2-、3-和4-羧基苯氧基自由基的生成焓，分别为Δf(2-HOOCC₆H₄O*, g) = -322.5 ± 3.0 kJ·mol⁻¹，Δf(3-HOOCC₆H₄O*, g) = -310.0 ± 3.0 kJ·mol⁻¹，Δf(4-HOOCC₆H₄O*, g) = -318.2 ± 3.0 kJ·mol⁻¹。2-OHBA、3-OHBA和4-OHBA中O-H键的解离焓分别为392.8 ± 3.3、383.6 ± 3.8和380.0 ± 3.4 kJ·mol⁻¹。最后，采用邻位-对位法发现，2-羧基苯氧基自由基中的H---O分子内氢键为25.7 kJ·mol⁻¹，比其母体（2-OHBA）中估计的氢键高约6 - 9 kJ·mol⁻¹，即20.2 kJ·mol⁻¹（理论值）或17.1 ± 2.1 kJ·mol⁻¹（实验值）。
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