【作者】 王冬梅；

【导师】 耿志远；

【作者基本信息】 西北师范大学 ， 无机化学， 2005， 硕士

【摘要】 草酸又称乙二酸,是最简单的二元酸,它异常的结构和独特的化学性质一直受到人们的关注,化学家们通过光谱检测、晶体结构分析、理论计算等多种手段对它及其卤代物进行了广泛地研究。在前人研究的基础上,本文采用高水平量子化学计算方法从理论上研究了草酸及其卤代物的基本构型、异构体构型、扭转势能面以及内转动过渡态,并选取了草酰溴作为代表体系对其进行了解离通道的研究。 全文包括七章,第一章主要回顾了草酸及其卤代物分子构型的研究进展状况。第二章概述了本文工作的量子化学的理论背景和基本计算方法。 第三章采用量子化学的MP2、B3LYP、HF计算方法在6-311++G^**水平上,对草酸可能存在的十三种构型进行完全放开的全几何优化及振动频率分析,得到八种稳定构型和五种内转动过渡态构型。并对最稳定构型在MP2/6-311++G^**水平上,作了NBO分析和MO分析,进而讨论了C-C键对草酸稳定性的影响以及草酸的结构与性质之间的关系。 第四章采用量子化学中从头算的方法HF、MP2、QCISD和密度泛函的方法B3LYP在6-311++G^**水平上对草酰氟中性分子（FCO）₂做了构像分析,得到了与光谱分析一致的结果,草酰氟分子有平面反式和顺式两种构像。在B3LYP/6-311++G^**水平上,分子轨道分析和自然键轨道分析（NBO）研究了两种构型的稳定性,根据频率分析计算结果进行振动模式分析,并模拟出红外光谱图,得到与实验相符的结果。 第五章用密度泛函方法BHandHLYP以6-311+GI（d）和6-311+G（2df）为基组对草酰溴一价正离子（BrCO）₂⁺和中性分子（BrCO）₂做了构像分析。结果表明,（BrCO）₂⁺和（BrCO）₂都具有平面反式和交叉式两种构像。交叉式构像存在超共轭现象。此外,对草酰溴离子、中性分子各解离通道初级反应的Gibbs自由能的计算,发现草酰溴离子C-C键解离通道的反应活性总体上大于中性分子,对该反应通道进一步做了反应机理研究,证实了热力学结论。 第六章对草酰溴分子的多键解离方式进行了DFT和CIS研究。计算表明:草酰溴分子基态（S₀）解离C-Br键不经过过渡态。吸收一个光子后,分子在第一电子激发态（S₁）解离生成高能态Br^·*和BrCOCO^·*自由基,此时体系很容易放出能量Q,变成基态的Br^·和BrCOCO^·自由基。放出的Q能量足以使BrCOCO^·自由基进一步热解为Br^·和2CO。与草酰氯所不同的是,BrCOCO^·自由基解离是一个协同的三体解离过程,即更多还原

【Abstract】 Oxalic acid is the simplest dualistic acid, its exceptional configuration and particular chemistry character is attended all along. Chemists widely study oxalic acid and oxalyl halides by spectrum detection, crystal structure analysis and theory calculation and so on. In this paper, high-level quantum chemistry calculation methods are used to theoretically investigate basic configuration, conformers, torsion potential energy surface and internal rotation transition state of oxalic acid and oxalyl halides. Oxalyl bromide as the typical system is studied on its dissociation channel.The whole paper consists of seven chapters. Chapter 1 mainly reviews the evolution of oxalic acid and oxalyl halides. The second chapter summarizes the theory of quantum chemistry and calculation methods of this paper.In the third chapter, the optimization and frequency analysis of thirteen possible structures of oxalic acid have been calculated, by using ab initio MP2, density functional method (B3LYP) and SCF-HF with 6-311++G** basis set. The results show that oxalic acid has eight local minima and five transition states of internal rotation configurations. Accordingly, The most stable isomer I has been analyzed with MO and NBO by using MP2/6-311++G** method. The effect of C-C bond on stability of oxalic acid is discussed, and the relationship between forms and characteristics of oxalic acid is also reported.In the fourth chapter, the configuration of oxalyl fluoride neutral molecule (FCO)2 is studied at HF MP2 QCISD and B3LYP level with 6-311++G** basis sets. The result that (FCO)2 have trans and gauche conformers are consist with spectrum analysis. At B3LYP/6-311++G** level, the stability of two conformers are studied by MO and NBO analysis. Furthermore, the vibrational mode is obtained by frequency analysis and IR spectrum chart is simulated, which is consisting with experiment result.In the fifth chapter, the conformers of oxalyl bromide cation (BrCO)+2 is studied at the BHandHLYP level with 6-311+G(d) and 6-311+G(2df) basis sets. It is found that (BrCO)+2 have trans and gauche conformers. Hyperconjugation exist in gauche form. Furthermore, the study of the dissociation reaction Gibbs free energy of oxalyl bromide cation (BrCO)+2 and neutral molecule (BrCO)2 show that the dissociation of C-C bond in (BrCO)+2 is easier更多还原