Density-Functional and Hartree-Fock Calculations on the Cyclopropane Ring Intermediates Involved in the Zeolite-Catalyzed Skeletal Isomerization of Hydrocarbons and in the Carbon-Isotope Scrambling in 2-Propyl Cation
Density-Functional and Hartree-Fock Calculations on the Cyclopropane Ring Intermediates Involved in the Zeolite-Catalyzed Skeletal Isomerization of Hydrocarbons and in the Carbon-Isotope Scrambling in 2-Propyl Cation
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DOI：
10.1021/jp964055s
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发表时间：
1997-07
影响因子：
3.3
通讯作者：
M. Frash;V. Kazansky;A. Rigby;V. Santen
中科院分区：
文献类型：
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作者：
M. Frash;V. Kazansky;A. Rigby;V. Santen
对分子筛催化环丙烷环中间体的烃骨架异构化反应机理进行了量子化学计算。根据B3 LYP/6- 31 G * 计算，由沸石中的表面烷氧基物质形成环丙烷经由过渡态发生，过渡态的烃部分类似于角质子化的环丙烷（角-PCP）环。两种构象的过渡态发现不同的PCP部分相对于酸位点的取向。环丙烷闭环反应的活化能被发现是相当敏感的平面对称性的限制和计算的水平和不太敏感的几何优化的水平。在几个理论水平上的高斯-2模型的自由2-丙基阳离子的碳同位素的混乱的机制进行了计算。相对稳定的中间体，这种超强酸催化反应是碳正离子，在相反的。
Quantum-chemical calculations were carried out on the mechanism of the zeolite-catalyzed hydrocarbon skeletal isomerization via the cyclopropane ring intermediates. According to the B3LYP/6-31G* calculations, formation of cyclopropane from surface alkoxy species in zeolites occurs via a transition state whose hydrocarbon part resembles a corner-protonated cyclopropane (corner-PCP) ring. Two conformations of the transition state found differ in the orientation of the PCP portion with respect to the acid site. The activation energy for the cyclopropane ring closure reaction is found to be rather sensitive to the use of planar symmetry constraints and to the level of calculations and less sensitive to the level of the geometry optimization. Calculations on the mechanism of the carbon isotope scrambling in the free 2-propyl cation were also performed, at several theory levels up to the Gaussian-2 model. The relatively stable intermediates of this superacid-catalyzed reaction are carbocations, in contrast to t...