Theoretical study of the heptamethylbenzenium ion. Intramolecular isomerizations and C2, C3, C4 alkene elimination.
Theoretical study of the heptamethylbenzenium ion. Intramolecular isomerizations and C2, C3, C4 alkene elimination.
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DOI：
10.1021/jp058166f
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发表时间：
2005-10
期刊：
影响因子：
--
通讯作者：
B. Arstad;S. Kolboe;O. Swang
中科院分区：
文献类型：
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作者：
B. Arstad;S. Kolboe;O. Swang
最近对H-Beta分子筛上甲醇合成碳氢化合物(MTH)反应的实验研究表明，七甲基苯是一个重要的中间体。我们进行了量子化学计算，研究了分子内异构化反应和从七MB+异构体中消除乙烯、丙烯和异丁烯等小烯烃的反应。研究了烯烃形成的两种反应途径：一种是从初始环收缩开始的，另一种是从七MB+离子的初始环扩张开始的。从最初的环收缩开始的反应导致双环物种，该物种可能分离出丙烯，或者在进一步的异构化之后，产生异丁烯。通过进一步的异构化，扩展到七元环可导致乙基和异丙基的形成，而乙基和异丙基又可分离为乙烯和丙烯。计算是在B3LYP/cc-pVTZ//B3LYP/6-311G(d，p)理论水平上进行的。在可能的情况下，与实验数据进行了比较。
Recent experimental work on the methanol-to-hydrocarbons (MTH) reaction in zeolite H-Beta suggests that the heptamethylbenzenium (heptaMB+) cation is an important intermediate. We have carried out quantum chemical calculations to investigate intramolecular isomerization reactions and eliminations of small alkenes such as ethene, propene, and isobutene from heptaMB+ isomers. Two types of reaction paths have been investigated for the alkene formation: One starting with an initial ring contraction, and one starting with an initial ring expansion of the heptaMB+ ion. The reaction starting with an initial ring contraction leads to a bicyclic species that may split off propene or, after further isomerizations, isobutene. Expansion to a seven-membered ring may, via further isomerizations, lead to formation of ethyl and isopropyl groups that may in turn be split off as ethene and propene. The calculations have been carried out at the B3LYP/cc-pVTZ//B3LYP/6-311G(d,p) level of theory with zero point energy corrections. Comparisons with experimental data are made where possible.