四氢萘微观结构的量子化学研究

为了研究氢化芳烃的微观结构,进一步认识和理解氢化芳烃在催化裂化过程中的反应特性。以四氢萘为模型化合物,利用基于密度泛函理论的量子化学从头计算方法,对四氢萘的几何结构和电子结构进行了系统研究,得到了四氢萘不同位置C-H键和C-C键的键长、键级、键能以及电子云密度、前线轨道分布等微观结构信息。发现四氢萘结构具有轴对称特性,苯环上的C-C键和C-H键要远比环烷环的C-C键和C-H键稳定。由于受苯环的影响,会使得其环烷环上不同位置的C-C键的键长、键级和键能均具有明显差异,也导致环烷环上不同位置C-H键的键长、键级和键能有较明显的差异,具体表现为:对C-C键而言,与苯环相连的C-C键的键长较短,键级较高,键能也明显较高,而苯环β位C-C键的键能则明显较低;对C-H键而言,与苯环β位环烷碳原子上的C-H键相比,苯环α位环烷碳原子上的C-H键的键能明显较低。电子云分布计算结果能够较好地给出的这些C-C键和C-H键结构特征差异的原因。前线轨道计算结果表明,在催化裂化过程中,苯环α位环烷碳原子上的C-H键和β位C-C键较易受到催化剂酸性中心的进攻,是酸催化反应的位点。这些计算结果对于认识与理解氢化芳烃的反应特性具有一定的基础性理论意义。

Quantum mechanical studies on the micro-structure of tetrahydro-naphthalene

In order to investigate the micro-structure of hydroaromatic hydrocarbons and further understand and comprend the reaction characterics of hydroaromatic hydrocarbons in catalytic cracking process,In this paper,density functional theory based quantum ab initio method has been selected to study the geometries and electronic structures of Tetrahydro-naphthalene(THNA),and quite a lot of microstructural parameters has been delivered,for example,the bond length,bond order,bond energy,electron cloud density and the figure of front molecular orbitail.It was found that THNA had a axisymmetric property,and both the C-C bonds and C-H bonds of benzene ring are stronger than those of naphthenic rings.Benzene ring had a very large impact on the C-C bonds and C-H bonds in different positions of naphthenic rings,so it would make a great difference among C-C bonds in different positions of naphthenic rings,and C-H bonds also varied largely in different positions of naphthenic rings.For the C-C bonds,Results showed that compared with other cyclic C-C bonds,the bond order and bong energy of the cyclic C-C bonds connected to the aromatic ring are much higher,and the bond length of the cyclic C-C bonds is much shorter.So the cyclic C-C bonds are much stronger than other cyclic C-C bonds,and the beta C-C bonds connected to the aromatic ring are clearly quite weak.For the C-H bonds,it has been found that the bond energy of alpha C-H bond of the aromatic ring is the lowest,so alpha C-H bond of the aromatic ring was the weakest C-H bond for THAN.The figure of electronic density distribution could reasonably explain these results,and the figure of frontier molecular orbital indicated that the alpha C-H bond of the aromatic ring and beta C-C bonds to the aromatic ring could be more easily attacked by acid sites.The alpha C-H bond of the aromatic ring and beta C-C bonds connected to the aromatic ring could be the reactive center for THAN.These results are very useful for understanding and comprending the reaction characterics of hydroaromatic hydrocarbons.