Chen Bo, Houk K N, Cammi Roberto
Donostia International Physics Center, Paseo Manuel de Lardizabal, 4, 20018, Donostia-San Sebastián, Spain.
IKERBASQUE, Basque Foundation for Science, Plaza Euskadi 5, 48009, Bilbao, Spain.
Chemistry. 2022 May 19;28(29):e202200246. doi: 10.1002/chem.202200246. Epub 2022 Apr 8.
Quantum chemical calculations are reported for the thermal dimerizations of 1,3-cyclohexadiene at 1 atm and high pressures up to the GPa range. Computed activation enthalpies of plausible dimerization pathways at 1 atm agree well with the experiment activation energies and the values from previous calculations. High-pressure reaction profiles, computed by the recently developed extreme pressure-polarizable continuum model (XP-PCM), show that the reduction of reaction barrier is more profound in concerted reactions than in stepwise reactions, which is rationalized on the basis of the volume profiles of different mechanisms. A clear shift of the transition state towards the reactant under pressure is revealed for the [6+4]-ene reaction by the calculations. The computed activation volumes by XP-PCM agree excellently with the experimental values, confirming the existence of competing mechanisms in the thermal dimerization of 1,3-cyclohexadiene.
报道了在1个大气压和高达吉帕范围的高压下1,3 - 环己二烯热二聚反应的量子化学计算。计算得到的1个大气压下可能二聚反应途径的活化焓与实验活化能以及先前计算的值吻合良好。通过最近开发的极端压力 - 极化连续介质模型（XP - PCM）计算得到的高压反应剖面图表明，协同反应中反应势垒的降低比逐步反应更为显著，这基于不同反应机理的体积剖面图得到了合理的解释。计算结果表明，对于[6 + 4] - 烯反应，在压力下过渡态明显向反应物方向移动。通过XP - PCM计算得到的活化体积与实验值非常吻合，证实了1,3 - 环己二烯热二聚反应中存在竞争反应机理。
