1,3-丁二烯及呋喃与硫甲醛杂Diels-Alder反应的理论研究

Ab initio theoretical study of the hetero Diels-Alder reactions of 1,3-butadiene and furan with thioformaldehyde

采用量子化学从头算方法在 HF/6 - 31G*及 MP2 /6 - 31G*水平上对 1,3-丁二烯及呋喃与硫甲醛间的杂 Diels- Alder反应进行了理论研究 .利用能量梯度法对反应途径上各驻点的几何构型进行了优化 ,对过渡态进行了振动分析确认 .结果表明 :两反应均为双分子基元反应 ,两反应中牵涉到的前线轨道 (FMO)相互作用主要是 1,3-丁二烯或呋喃分子的最高占据轨道 (HOMO)与硫甲醛分子的最低空轨道 (L UMO)间的相互作用 ,在 MP2 /6 - 31G*水平所计算的两反应的活化势垒分别为 3.70 k J· mol- 1及 9.5 8k J· mol- 1 ,这与实验上所观察到的 1,3-丁二烯及呋喃容易与硫羰基化合物发生杂 Diels- Alder反应的实验现象是一致的 .

An ab initio theoretical study of the hetero Diels Alder cycloadditions of 1,3 butadiene and furan to thioformaldehyde has been presented. The structures of the reactants, transition states and products were completely optimized by the Berny energy gradient technique at the HF/6 31G * and MP2/6 31G * theory levels, and the transition states were characterized by vibration frequency analysis. The two reactions are found to proceed via a concerted mechanism and are LUMO dienophile and HOMO diene controlled, due to a low lying LOMO of thioformaldehyde. The two reactions are predicted to have a barrier height of 3.70 or 9.58 kJ·mol -1 respectively at the MP2/6 31G * level of theory and this is consistent with the experimental fact.