水杨酸的分子内 O···H 氢键：使用 DFT 计算进一步了解 O 1s XPS 和 1H NMR 光谱,The Journal of Physical Chemistry A

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水杨酸的分子内 O···H 氢键：使用 DFT 计算进一步了解 O 1s XPS 和 1H NMR 光谱
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2023-03-20 , DOI: 10.1021/acs.jpca.2c08981
Alexander Hill ₁ , Feng Wang ₁

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分子内氢键 (HB) 是一种复杂的现象，它超越了简单的价事件，影响了分子的核心电子。水杨酸 (SA) 及其构象异构体为研究分子内 HB 提供了极好的模型化合物，因为质子供体 (H) 和受体 (O) 可以通过旋转 C-O 和 C-C 键来切换，形成多达七个潜在的构象异构体通过各种HB。^{在这项研究中，我们通过检查计算的 O 1s 核心电子结合能 (CEBE) 和使用最近的测量验证的1} H NMR 化学位移，计算研究了有和没有这种 HB 的 SA 构象异构体中的分子内相互作用。量子力学稳定的 SA 构象异构体完全由化合物中的三个可旋转键定义，抽象为 SA(η ₁ η₂ η ₃ ) 数字结构，其中 η _i = 0 如果 η _i角与最稳定的 SA 构象 (000) 匹配，否则 η _i = 1。我们的研究结果表明，稳定性受 H _p ···O 的基团间 HB 的出现（其中 O 在羧酸官能团中，H _{p是 −OH}_p中的酚质子）和 η ₃的影响作为此类 HB 的开关。因此，包含这种 Hp ···O HB 的 (η ₁_η 2 ₀ ) SA 构象异构体比其他 SA 构象异构体 (η ₁ η ₂1) 没有这样的H _p ···O HB。目前的密度泛函理论计算表明，这种 H _p ···O HB 导致两个羟基 (-OH) 的 O 1s CEBE 分裂高达 1 eV，并使 H _p质子¹ H NMR (δH _p )去屏蔽(η ₁ η ₂ 0) 构象异构体高达 11.68 ppm 。如果没有这样的 H _p ···O HB，两个 −OH 基团的 O 1s XPS 结合能将紧密地位于同一波段，并且H _p的^{1 H NMR 化学位移}原子将小到 4.09 ppm SA 构象 [SA-G(101)]。_{本研究表明 O 1s CEBE 分裂在两个 -OH 基团之间作为 SA 构象异构体中 H p} ···O HB存在的指示，这也得到¹ H NMR 结果的支持。

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Intramolecular O···H Hydrogen Bonding of Salicylic Acid: Further Insights from O 1s XPS and 1H NMR Spectra Using DFT Calculations

Intramolecular hydrogen bonding (HB) is a complex phenomenon that extends beyond a simple valence event, affecting the core electrons of a molecule. Salicylic acid (SA) and its conformers provide an excellent model compound for studying intramolecular HB as the proton donor (H) and acceptor (O) can be toggled by rotating the C–O and C–C bonds to form up to seven potential conformers through various HB. In this study, we computationally investigated intramolecular interactions in SA conformers with and without such HB, by examining their calculated O 1s core electron-binding energy (CEBE) and ¹H NMR chemical shifts validated using recent measurements. The quantum mechanically stable SA conformers are fully defined by three rotatable bonds in the compound, which are abstracted as SA(η₁η₂η₃) digital structures, where η_i = 0 if the η_i angles match the most stable SA conformer (000) and η_i = 1 otherwise. Our findings suggest that the stability is dominated by the appearance of the intergroup intramolecular HB of H_p···O (where O is in the carboxylic acid functional group and H_p is the phenolic proton in −OH_p), and η₃ serves as a switch of such HB. As a result, the (η₁η₂0) SA conformers containing such H_p···O HB are more stable than other SA conformers (η₁η₂1) without such the H_p···O HB. The present density functional theory calculations reveal that this H_p···O HB results in splitting of the O 1s CEBEs of two hydroxyl groups (−OH) by up to 1 eV and deshielding the H_p proton ¹H NMR (δH_p) up to 11.68 ppm for the (η₁η₂0) conformers. Without such H_p···O HB, the O 1s XPS binding energies of two −OH groups will be closely located in the same band, and the ¹H NMR chemical shift of the H_p atom will be as small as an 4.09 ppm SA conformer [SA-G(101)]. The present study indicates that the O 1s CEBE splitting between two −OH groups serves as an indicator of the presence of the H_p···O HB in SA conformers, which is also supported by the ¹H NMR results.

更新日期：2023-03-20

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