Experimental and Theoretical Multiple Kinetic Isotope Effects for an SN2 Reaction. An Attempt to Determine Transition-State Structure and the Ability of Theoretical Methods to Predict Experimental Kinetic Isotope Effects
作者:Yao-ren Fang、Ying Gao、Per Ryberg、Jonas Eriksson、Magdalena Kołodziejska-Huben、Agnieszka Dybała-Defratyka、S. Madhavan、Rolf Danielsson、Piotr Paneth、Olle Matsson、Kenneth Charles Westaway
DOI:10.1002/chem.200204119
日期:2003.6.16
alpha-carbon kinetic isotope effects (KIEs) and activation parameters have been measured for the S(N)2 reaction between tetrabutylammonium cyanide and ethyl chloride in DMSO at 30 degrees C. Then, thirty-nine readily available different theoretical methods, both including and excluding solvent, were used to calculate the structure of the transition state, the activation energy, and the kinetic isotope effects
仲α-氘,仲β-氘,氯离去基团,亲核仲氮,亲核体(12)C /(13)C碳和(11)C /(14)Cα-碳已测定了DMSO在30℃下四丁基氰化铵与氯乙烷之间的S(N)2反应的动力学同位素效应(KIEs)和活化参数。然后,三十九种容易获得的不同理论方法,包括和不包括溶剂,用来计算过渡态的结构,活化能和反应的动力学同位素效应。通过使用半经验,从头算和密度泛函理论方法对实验和理论结果进行的比较表明,密度泛函方法在计算实验同位素效应方面最为成功。除了两个例外,在计算中包括溶剂并不能提高与实验性KIE的拟合度。最后,从理论方法获得的过渡态和力常数都无法预测实验发现的所有六个KIE。而且,没有一个计算出来的过渡结构(都是早期且松散的)与通过解释实验性KIE所建议的晚期(产品状)过渡态结构相吻合。