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Explanation of Theoretical Mechanism of Isomerization of L-Alanine Conformation for Experimental Results

《结构化学》2013年 第9期 | 姜华 孟祥军   School of Chemistry and Materials Science Ludong University Department of Chemistry Tangshan Normal College
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摘 要:B3LYP/6-31++G**method was applied to investigate the mechanism of alanine isomerization.12 minima and 22 transition states were obtained after optimization and several paths of isomerization were found.It is found that intramolecular single-bond rotation and proton transfer might lead to isomerization.The energy barrier of C–N bond rotation was lower than 2.52kcal·mol 1,while the energy barrier ranges of the rotation of C–C and C–O were separately 0.43~7.01 and 4.69~12.19 kcal·mol 1,and the minimum energy barrier of proton transfer was 30.76kcal·mol 1.The most probable isomerization path and mechanism for the two most stable conformations was discussed to find that the highest energy barrier to be crossed in this path was11.87 kcal·mol 1.In order to understand the microscopic nature why only 4 conformations were detected in the experiment,thermodynamic properties of all conformations at the experimental temperature of 391K was calculated.It is found that conformations XII,XI,X and IX can only unidirectionally convert into conformations rapidly with low energy and vanish immediately.The other conformations were distributed according to Maxwell-Boltzman’s law,and the distribution probabilities of conformations I,II,III,IV,V,VI,VII and VIII were respectively 27.2%,26.5%,25.8%,6.4%,5.2%,4.8%,2.5%and 1.6%.Conformations I,II and III with bigger probability and stronger absorption peak were easy to detect in the experiment.Conformation IV had a relatively smaller probability(6.4%)and weak absorption peak which,however,could also be identified.The other conformations had too small probability to identify in the spectrum.
【分 类】【数理科学和化学】 > 化学 > 有机化学 > 元素有机化合物 > 第Ⅲ族元素有机化合物 > 硼有机化合物、铝有机化合物【工业技术】 > 化学工业 > 其他化学工业 > 发酵工业 > 发酵法制氨基酸 > 丙氨酸
【关键词】 异构化反应 L-丙氨酸 实验温度 构象 解析 机理 分布概率 质子转移
【出 处】 《结构化学》2013年 第9期 1316-1324页 共9页
【收 录】 中文科技期刊数据库