Probing the acid-base equilibrium in acid-benzimidazole complexes by 1H NMR spectra and density functional theory calculations.
Probing the acid-base equilibrium in acid-benzimidazole complexes by 1H NMR spectra and density functional theory calculations.
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DOI：
10.1021/jp1054606
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发表时间：
2010-09
期刊：
影响因子：
--
通讯作者：
Dongfang Zhang;Liuming Yan
中科院分区：
文献类型：
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作者：
Dongfang Zhang;Liuming Yan
用（1）H NMR谱、FTIR谱和密度泛函理论（DFT）计算研究了苯并咪唑（BIm）与酸（苯膦酸、甲磺酸、磷酸、盐酸、乙酸和硫酸）配合物的酸碱平衡。DFT优化的酸-BIm复合物的结构，酸性质子的振动频率，和电位分布被施加到研究酸和BIm之间的平衡。结果表明，在气相中，浓硫酸能使BIm完全质子化，其它酸只能使BIm不完全质子化。当应用DMSO的极化连续模型时，结果表明，除了弱乙酸和苯基膦酸外，所有的酸都可以完全质子化BIm。此外，PPoA-BIm的电位分布显示出双阱结构，有利于酸性质子在PPoA和BIm之间的自由移动。如果DMSO的明确溶剂分子被包括到酸-BIm复合物中，则观察到酸和BIm之间的平衡的显著变化。MSA-BIm和HCl-BIm的电位分布显示出非常平底的威尔斯阱，促进了质子在酸和BIm之间的自由移动。这些计算与苯并咪唑环在DMSO-d（6）中的固定质子的（1）H NMR化学位移和酸-BIm络合物的FTIR光谱一致。
The acid-base equilibrium in acid (phenylphosphonic acid, methylsulfonic acid, phosphoric acid, hydrochloric acid, acetic acid, and sulfuric acid)-benzimidazole (BIm) complexes was studied by (1)H NMR spectra, FTIR spectra, and density functional theory (DFT) calculations. The DFT optimized structures of the acid-BIm complexes, the vibrational frequencies of the acidic protons, and potential profiles were applied to study the equilibrium between the acids and BIm. In gas phase, it was shown that the strong sulfuric acid could completely protonate BIm and the other acids could only incompletely protonate BIm. When the polarizable continuum model of DMSO was applied, it was shown that all the acids could completely protonate BIm, except the weak acetic acid and phenylphosphonic acid. Furthermore, the potential profile for the PPoA-BIm shows double-well structure facilitating the free movement of the acidic proton between PPoA and BIm. If an explicit solvent molecule of DMSO was included into an acid-BIm complex, significant changes in equilibrium between acid and BIm are observed. The potential profiles for the MSA-BIm and HCl-BIm show very flat bottom wells, facilitating the free movement of proton between the acid and BIm. These calculations were consistent with the (1)H NMR chemical shifts of the immobile protons of the benzimidazole ring in DMSO-d(6) and the FTIR spectra of the acid-BIm complexes.