Theoretical analysis of kinetic isotope effects on proton transfer reactions between substituted alpha-methoxystyrenes and substituted acetic acids.
Theoretical analysis of kinetic isotope effects on proton transfer reactions between substituted alpha-methoxystyrenes and substituted acetic acids.
复制标题
动力学同位素对取代的α-甲氧基形式和取代乙酸之间质子转移反应的理论分析。
DOI：
10.1021/ja905081x
复制
发表时间：
2009-10-07
影响因子：
15
通讯作者：
Gao, Jiali
中科院分区：
文献类型：
--
作者：
Wong, Kin-Yiu;Richard, John P.;Gao, Jiali
采用Kleinert变分二阶微扰理论（KP 2），在Feynman路径积分（PI）沿着B3 LYP/6-31+G（d，p）水平下，计算了羧酸催化的芳基取代α-甲氧基苯乙烯（X-1）质子化生成氧代碳正离子反应的初级动力学同位素效应（KIE）.与实验数据吻合良好，表明这种新的计算方法用于计算有机反应的KIE是一个可行的替代传统的方法采用Bigeleisen方程和谐波振动频率。虽然隧道效应对羧酸催化的质子化反应的自由能垒的降低贡献相对较小，但为了获得KIE的定量估计，有必要包括隧道效应的贡献。对取代α-甲氧基苯乙烯与氯乙酸的质子化反应，考虑非谐性可以进一步提高计算的KIE，但对母体和4-NO2取代α-甲氧基苯乙烯与取代羧酸的反应，非谐性的修正高估了计算的KIE。与实验结果一致，最大的KIE被发现在近功中性反应中，ΔGo = 0，其中过渡结构是近对称的，反应势垒相对较低。此外，优化的过渡结构强烈依赖于形成碳阳离子中间体的自由能，即，驱动力ΔGo，沿着与过渡态结构中的哈蒙德位移有很好的相关性。
Primary kinetic isotope effects (KIEs) on a series of carboxylic acid-catalyzed protonation reactions of aryl-substituted α-methoxystyrenes (X-1) to form oxocarbenium ions have been computed using the Kleinert variational second-order perturbation theory (KP2) in the framework of Feynman path integrals (PI) along with the potential energy surface obtained at the B3LYP/6-31+G(d,p) level. Good agreement with the experimental data was obtained, demonstrating that this novel computational approach for computing KIEs of organic reactions is a viable alternative to the traditional method employing Bigeleisen equation and harmonic vibrational frequencies. Although tunneling makes relative small contributions to the lowering of the free energy barriers for the carboxylic acid catalyzed protonation reaction, it is necessary to include tunneling contributions to obtain quantitative estimates of the KIEs. Consideration of anharmonicity can further improve the calculated KIEs for the protonation of substituted α-methoxystyrenes by chloroacetic acid, but for the reactions of the parent and 4-NO2 substituted α-methoxystyrene with substituted carboxylic acids, the correction of anharmonicity overestimates the computed KIEs for strong acid catalysts. In agreement with experimental findings, the largest KIEs are found in nearly ergoneutral reactions, ΔGo ≈ 0, where the transition structures are nearly symmetric and the reaction barriers are relatively low. Furthermore, the optimized transition structures are strongly dependent on the free energy for the formation of the carbocation intermediate, i.e., the driving force ΔGo, along with a good correlation of Hammond shift in the transition state structure.
登录
查看更多内容
影响因子：
3
作者：
CAMMI, R;TOMASI, J
通讯作者：
TOMASI, J
影响因子：
15
作者：
JARRET, RM;SAUNDERS, M
通讯作者：
SAUNDERS, M
影响因子：
4.4
作者：
BECKE, AD
通讯作者：
BECKE, AD
影响因子：
4.4
作者：
Barone, V;Cossi, M;Tomasi, J
通讯作者：
Tomasi, J
影响因子：
2.9
作者：
Jang, S;Schwieters, CD;Voth, GA
通讯作者：
Voth, GA