SO_2钳合反应机理的密度泛函研究

DFT Study on the Mechanism of Cheletropic Addition of SO_2

采用密度泛函理论(DFT)在B3LYP/6-311+G**水平上计算了SO2与2,4-己二烯之间的钳合反应,IRC计算结果表明该反应是协同反应.反应中,这两个反应物同时把自己的HOMO电子填入对方的LUMO轨道,这与传统的4+2环加成机理不同.反应前SO2的HOMO轨道与2,4-己二烯的LUMO轨道之间能级相差很大(8.4eV),但随着反应进行,2,4-己二烯的反键LUMO轨道逐渐演变成一个成键轨道,能级下降,使得SO2的HOMO上电子可以向该轨道流动.反应的净结果是有0.23e的负电荷由SO2向2,4-己二烯转移.

Cheletropic addition of sulfur dioxide to 2,4-hexadiene has been calculated by density functional theory （DFT） at the level of B3LYP/6-311 ＋G^＊＊, the result of IRC calculation shows that the cheletropic addition is a concerted reaction. In reaction, each reactant gives its electrons in HOMO to the LUMO of other reactant simultaneously, which is different from the conditional mechanism of 4 ＋ 2 cycloaddition. Before reaction, the difference of energy level between HOMO of sulfur dioxide and LUMO of 2,4-hexadiene is largish（8.4 eV）, but in the course of reaction, the antibonding LUMO of 2,4-hexadiene turns into a bonding orbital and decreases its energy, so the electrons in HOMO of sulfur dioxide can flow into this orbital easily. The net result of the reaction is that sulfur dioxide transfers 0.23e negative charge to 2,4-hexadiene.