2-氯吡啶光氯化取代反应机理的量子化学研究

Theoretical Study on Substitute Mechanism of Chlorine Radical with 2-Chloropyridine

用PM3方法研究了2-氯吡啶光氯化取代反应的过渡态.研究结果表明,生成2,6-二氯吡啶、2,5-二氯吡啶、2,4-二氯吡啶、2,3-二氯吡啶不同产物的每一个反应通道都存在两个过渡态;反应体系沿反应坐标的变化为反应物→反应物络合物→第1过渡态→中间体→第2过渡态→产物络合物→产物;第2过渡态为主过渡态,生成2,6-二氯吡啶反应路径主过渡态的能量及活化能最低,分别为-139612.06和135.39kJ/mol,反应优先生成2,6-二氯吡啶.生成二氯吡啶反应过程中吡啶环反应部位CCl键的形成主要与共轭双键断裂同步,而CH键的断裂主要与共轭双键的重新形成同步.

The substitute mechanism of 2-chloropyridine reacting with chlorine radical was studied theoretically by semi-empirical method- PM3. The results showed that there were two transition states in each reaction path for obtaining 2,3-,2,4-,2,5-and 2,6-dichloropyridine respecively. The energy of chief transition state and activation barrier of leading to 2,6-dichloropyridine were lowest among four reaction paths, which is -139 612.06 and 135.39 kJ/mol respectively. Thus, 2,6-dichloropyridine was prior product. The formation ofC (Cl) and the breaking of conjugate double bond was mainly synchronous during the process of producing the dichloropyridine, so did the breaking of C H bond and the re-formation of conjugate double bond.