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为了研究催化裂化过程中,烷烃分子中的C-H键和C-C键质子化产生具有三中心两电子键结构的CHH和CHC五配位正碳离子之间的转化反应。利用密度泛函理论的量子化学从头算法,计算了正十六烷分子链中C_4-H键和与之相邻的C_3-C_4键和C_4-C_5键质子化形成的C_4HH、C_3HC_4和C_4HC_5五配位正碳离子的结构和能量。结果表明,正十六烷质子化产生的CHH五配位正碳离子能量高于C_3HC_4和C_4HC_5五配位正碳离子。表明CHH五配位正碳离子能够转化为CHC五配位正碳离子。以C_4HH、C_3HC_4和C_4HC_5五配位正碳离子为起点进行过渡态搜索,得到了C_4HH五配位正碳离子转化为C_3HC_4和C_4HC_5五配位正碳离子的过渡态,并对过渡态进行了确认。计算得到的C_4HH五配位正碳离子转化为C_3HC_4和C_4HC_5五配位正碳离子的能垒分别为16.6kJ/mol和13.9 kJ/mol,表明CHH五配位正碳离子很容易转化为CHC五配位正碳离子。
In order to study the catalytic cracking process, the protonation of the C-H bond and the C-C bond in the alkane molecule resulted in the conversion reaction between the pentacoordinated carbon ions of CHH and CHC having a three-center two-electron bond structure. C_4HH, C_3HC_4 and C_4HC_5 protonated C_4-H bond, C_4-C_4 bond and C_4-C_5 bond in the n-hexadecane molecular chain were calculated using the ab initio quantum-chemical density functional theory The structure and energy of a positive carbon ion. The results showed that the energy of protonated CHH pentacyclic carbons produced by n-hexadecane protonation is higher than that of C_3HC_4 and C_4HC_5 pentacoordinated carbon ions. Show that CHH five coordinated carbon ions can be converted into CHC five coordinate carbon ions. The C_4HH, C_3HC_4 and C_4HC_5 pentacoordinated carbon ions as a starting point for the transition state search, obtained C_4HH pentacoordinated carbon ions into C_3HC_4 and C_4HC_5 five coordination carbon ion transition state was confirmed and the transition state . The calculated energy barriers for the conversion of C_4HH pentacoordinate carbon to C_3HC_4 and C_4HC_5 pentacoordinated carbon are 16.6 kJ / mol and 13.9 kJ / mol, respectively, indicating that CHH pentavalent carbon is easily converted to CHC Coordination is carbon.