低阶煤中氢键作用的色散校正密度泛函理论研究

本研究以苯酚…苯酚、苯酚…苯、苯酚…二苯醚、苯酚…喹啉和苯甲酸…苯甲酸为对象，采用色散校正的密度泛函理论分别研究褐煤中自缔合OH、OH-π、OH-醚O、OH-N和COOH-COOH之间形成的氢键。此外，还研究了氢键供体中取代基(CH₃-、CH₃O-、OH-、NH₂-、COOH-和NO₂-)对氢键的影响。对上述复合物进行了几何优化，并计算了能量、Mulliken电荷分布及振动频率。从优化的结构中可以看出上述复合物之间都存在氢键，所有复合物中O-H键键长都比苯酚中自由羟基的长，这表明这些复合物之间存在相互作用。其中，羧酸…羧酸复合物中O-H键的键长最长。此外，通过Mulliken电荷分布可看出上述复合物之间存在电荷转移。基于振动频率分析，所有的O-H键伸缩振动都发生了红移，尤其是羧酸…羧酸和苯酚…喹啉复合物，这可为煤中羟基振动的红外光谱分析提供依据。根据键能不同氢键强度按以下顺序依次递减：COOH-COOH>OH-N > 自缔合OH≈OH-醚O > OH-π，这与振动频率的分析结果一致。此外，不同取代基对氢键作用的影响不同。

Simulation of hydrogen bonds in low-rank coals with lignite-related complexes using dispersion corrected density functional theory

Phenol…phenol, phenol…benzene, phenol…oxydibenzene, phenol…quinoline, and benzoic acid…benzoic acid were selected as lignite-related complexes to investigate different hydrogen bonds formed by self-associated OH, OH-π, OH-ether O, OH-N, and COOH-COOH using density functional theory with dispersion correction, respectively. Moreover, the effects of substituents (CH₃-, CH₃O-, OH-, NH₂-, COOH-, and NO₂-) in donors on the hydrogen bonds were investigated. Geometry optimization, energy, Mulliken population, and frequency of all the complexes were calculated. It can be seen from optimized structures that there indeed are hydrogen bonds in the different complexes. Bond lengths of all O-H bonds in the different complexes become longer than that of free OH in phenol, which implies that intermolecular interactions exist in all the complexes. Among of them, bond lengths of O-H bonds in benzoic acid…benzoic acid are the longest. In addition, charge transfer can be observed via Mulliken population. Based on frequency analysis, all O-H stretching vibrations have obvious red shift, especially O-H bonds in benzoic acid…benzoic acid and phenol…quinoline, which gives evidence of using the infrared spectroscopy to analyze hydroxyl groups of coals. According to bond energies, the strength of the different hydrogen bonds decreases in the order: COOH-COOH > OH-N > self-associated OH ≈ OH-ether O > OH-π, which is consistent with the reported experimental results. Different substituents have distinct effects on the hydrogen bonds.