吡啶与苄基溴衍生物Menschutkin反应的溶剂和取代基效应的理论研究

Theoretical study of solvent and substituent effects on Menschutkin reactions between pyridine and benzyl bromide derivatives

利用MP2/6-311++G(d,p)//B3LYP/6-31+G(d,p)方法和SMD溶剂化模型研究苄基溴及其衍生物和吡啶在气相和乙腈溶剂中的Menschutkin反应机理,对其主要的两条反应途径:吡啶由溴的异侧或同侧进攻,进行理论计算,解释乙腈溶剂及取代基对反应机理的影响。计算结果表明,在气相和乙腈中,吡啶从苄基溴的异侧进攻时为反应的优势途径,而且在乙腈中比在气相中更容易发生反应;该反应是一个协同非同步的反应;苄基溴及其衍生物随着取代基性质、位置不同,与吡啶在气相与溶剂中发生的反应机理相似;在乙腈中,取代基影响反应速率变化的趋势与实验结果相吻合。

The mechanisms of the Menschutkin reactions between pyridine and benzyl bromide derivatives were explored in the gas phase and acetonitrile solution by means of the MP2/6-311++G(d,p)//B3LYP/6-31+G(d,p)method combined with the solvation SMD model.Two possible pathways were considered,namely,pyridine attacks benzyl bromide by the opposite(path1)and same(path2)sides of bromine atom,respectively.The solvent and substituent effects on this reaction were also investigated.The calculated results show that pyridine prefers to attack bromine from the opposite side of benzyl bromide in both gas phase and acetonitrile solution,and the reaction is more favorable in the acetonitrile solution than in the gas phase.The reaction is a synergistic and asynchronous process in both gas phase and acetonitrile.In solution,the reaction rate increases as the enhancing of electron donating ability of substituent in benzyl bromide derivatives,which is well consistent with the experimental observes.