固相二乙炔拓扑化学聚合的量子化学研究

Quantum-Chemical Investigation on the Topochemical Polymerization of Solid-State Diacetylenes

利用协同反应模型和ＥＨＣＯ－ＡＳＥＤ量子化学方法，对具有不同侧基的固态二乙炔拓扑聚合反应的势能曲线进行了计算，并对其轨道对称性以及能隙随反应坐标的变化进行了分析。很好地解决了文献中用Ｗｏｏｄｗａｒｄ－Ｈｏｆｆｍａｎｎ轨道对称守恒原理对此类反应进行分析的结果与实验事实相矛盾的问题，指出了此类反应既是光允许，也可以是热允许的原因。对此类反应的侧基效应进行的研究结果表明，侧基电子亲和势的变化对该类反应的反应机理及活化能影响较小，但对产物热力学稳定性的影响则较为显著。

The potential curves of the polymerization of solid-state diacetylenes (MDA→PBT→PDA) with different side groups R have been studied based on the topochemical model and the quantum-chemical method of EHCO-ASED. Twonecessary conditions must be satisfied for the reactions to take place: (1) The geometric parameters must undergo a series of concerted changes to make the conformation suitable for the intermolecular 1,4-addition, which should overcome an energy barrier Eb (2) The symmetry match between the frontier crystal orbitals of the reactant the product must be satisfied-electrons of the reactant must be excited from HOCO into LUCO, which faces an energy gap Eg. At state MDA, there is Eg(MDA)￣5.6 eV, if MDA and PDA are analyzed according to Woodward-Hoffmann's rules, this reaction would be considered photochemically allowed but thermochemically forbidden. It has been shown that Eg gradually decreases along the reaction coordinate from state MDA to PBT. At state PBT there is Eg(PBT)￣0 eV, and the electrons of the reactant can be easily excited there. Since Eb￣1.0 eV is not very large and Eg(PBT) is very small, the two necessary conditions mentioned above can be satisfied thermally.Therefore, thermal polymerization may take place smoothly. We have also investigated the effect of side group (R) on such reactions. The calculated results reveal that side group affect little on the activation energies of the reactions,but there is a significant influence on the thermal stability of the products (PDA).