【作者】 倪杰；

【导师】 黎安勇；

【作者基本信息】 西南大学 ， 物理化学， 2009， 硕士

【摘要】 我们之前的研究工作发现HNO、HNS、HCHO等具有强的分子内超共轭,它们在作为质子给体形成的氢键中起着重要作用;而且也可以作为质子受体形成氢键,在这两种情况下分子内超共轭起着不同的作用。为了探索这个问题,本文运用量子化学从头算计算方法对它们形成的氢键及分子间相互作用进行了研究,并利用现有的氢键理论解释其形成的机理。主要内容如下:1.运用量子化学从头算方法研究了HNO与分子簇（HF）_1≤n≤3形成的蓝移与红移氢键。在这些体系中,F…H-N都是监移氢键,重极化与重杂化利分子内超共轭导致了氢键的监移;所有的x…H-F（X=O,N,F）氢键都是红移的,分子间超共轭导致了氢键的红移。在多分子体系形成的氢键链中,分子间超共轭作用呈现规律性递变,它导致了氢键强度与频率位移的规律性变化,电子密度拓扑分析结果反映和支持了这种规律性变化。2.运用量子化学从头算方法研究了HNO（HNS）与（HF）_1≤n≤3形成的蓝移氢键。计算结果表明:在HNO体系中,氢键NH…F的形成导致NH键收缩与伸缩振动频率蓝移,且随着n增大而增大;在HNS体系中,NH键是微小监移的,但键长增大,n相同时,NH键蓝移比HNO体系的小很多。电子密度拓扑（AIM）分析阐明了这些分子间相互作用的氢键性质。自然键轨道（NBO）分析表明,在HNO体系中,重极化和重杂化以及分子内超共轭大幅度减小导致了NH键的监移:而HNS体系中NH键蓝移很小主要是由于n（S）的超共轭给予能力比n（O）小,因而对σ^*（NH）电子密度的调节能力小的缘故。3.运用量子化学从头算的MP2方法,分别在6-311++G（d,p）,6-311++G（2df,2p）,6-311++G（3df,3pd）,aug-cc-pVDZ,aug-cc-pVTZ基组下,研究了HCHO和HNO二聚体、三聚体形成的氢键。计算结果表明:在这些体系中,C（N）-H键收缩,伸缩振动频率增大,形成O…H-C（N）蓝移氢键,且蓝移较大(都超过87cm^-1)。AIM分析结果表明,在四种复合物中,O…H-C（N）之间都存在键临界点,并且都存在环临界点,形成稳定的环状复合物。NBO分析表明,分子内超共轭比分子间超共轭占明显优势;存在一定程度的重杂化。这些因素共同导致O…H-C（N）氢键的蓝移。更多还原

【Abstract】 In the present paper,ab initio quantum mechanics method（MP2） is employed to investigate the origin of hydrogen bond among HNO、HNS and HCHO so on,especially the effect on hydrogen bonds of intramolecular hyperconjugation.The main contents are the following:1.Quantum chemistry ab initio methods were applied to study the blue- and red-shifted H-bonds between HNO and（HF）_1≤n≤3.In these systems,all of the F…H-N H-bonds are blue-shifted, and the blue shifts are caused by repolarization,rehybridization,and intramolecular hyperconjugation;all of the X…H-F（X = O,N,F） are red-shifted,intermolecular hyperconjugation leads to the red shifts.In these chains of H-bonds,the variations of intermolecular hyperconjugations, electron densities at the bond critical points（BCPs）,and strength and frequency shifts of the H-bonds are correlated with each other and have definite rules.2.The blue-shifted H-bonds between HNO（HNS） and（HF）_1≤n≤3 have been theoretically studied. The calculated results show that in the HNO systems the H-bonds NH…F lead to large contraction of NH bonds and large blue shifts of NH stretch frequency which increase with n,and that in the HNS systems the blue shifts of NH stretch frequency are much smaller than those in the HNO system with the same n.The topological analysis of electron density demonstrates that these interactions are indeed H-bonds.The natural bond orbital analysis shows that in the HNO systems the blue-shifted H-bonds are caused by repolarization and rehybridization and decrease of intramolecular hyperconjugation,but in the HNS systems the reason that the blue shifts of NH bonds are very small is that the ability of hyperconjugation donation and adjustability on electron density inσ^*（NH） of n（S） is much smaller than that of n（O）.3.Ab initio quantum mechanics method（MP2） is employed to investigate the H-bonds in the dimmers and tripolymers of HCHO and HNO with the 6-311++G（d,p）,6-311++G（2df,2p）, 6-311++G（3df,3pd）,aug-cc-pVDZ,aug-cc-pVTZ basis sets.In the four complexes,C（N）-H…O blue shifting H-bond is formed where C（N）-H bond contracts and the corresponding stretching frequency blue shifts larger than 87cm^-1.The topological properties of the electron density of the H-bonds C（N）-H…O are usual linear H-bonds,there is a bond critical point between Y and each hydrogen,and a ring critical point inside each complexes.The NBO analysis shows that three main factors lead to the formation of these blue-shifted H-bonds:（a） intermolecular hyperconjugation is very small and can be neglected;（b） decrease of intramolecular hyperconjugation leads to decrease of occupancy inσ^*（C-H） andσ^*（N-H）;（c） there exists rehybridization.更多还原