Poland Kimberley N, Yang Weiwei, Fortenberry Ryan C, Davis Steven R
Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi, USA.
Phys Chem Chem Phys. 2022 Jun 15;24(23):14573-14578. doi: 10.1039/d2cp00794k.
The isomerization of the highly strained benzvalyne structure to -benzyne has been investigated using MCSCF and CCSD(T) levels of theory. Two reaction channels were modeled: the disrotatory one which leads directly to the benzyne product, and the conrotatory one which leads to an intermediate which can subsequently lead to the benzyne product. Energies at the MRMP2 level give 22.9 kcal mol for the disrotatory channel and 21.7 and 1.4 kcal mol for the two steps in the conrotatory one. However, the CCSD(T) energies give 19.3 and 14.2 kcal mol for the two conrotatory steps. The first step of the conrotatory channel is significantly higher than the second so is rate determining for this channel. Comparison of the two separate channels shows that the conrotatory has just a slight energetic edge of 1.2 kcal mol at the MRMP2 level. We did not compute the disrotatory channel at the CCSD(T) level due to the significant biradical nature of the wavefunction with natural orbital occupation numbers of 1.2 and 0.8 in the active space.
已使用MCSCF和CCSD(T)理论水平研究了高张力苯并戊炔结构异构化为苯炔的过程。对两个反应通道进行了建模：直接生成苯炔产物的顺旋通道，以及生成中间体随后再生成苯炔产物的对旋通道。MRMP2水平的能量显示，顺旋通道为22.9 kcal/mol，对旋通道的两步分别为21.7 kcal/mol和1.4 kcal/mol。然而，CCSD(T)能量显示对旋通道的两步分别为19.3 kcal/mol和14.2 kcal/mol。对旋通道的第一步明显高于第二步，因此是该通道的速率决定步骤。对两个独立通道的比较表明，在MRMP2水平上，对旋通道仅具有1.2 kcal/mol的微弱能量优势。由于活性空间中自然轨道占据数为1.2和0.8的波函数具有显著的双自由基性质，我们未在CCSD(T)水平计算顺旋通道。
