Direct Experimental Determination of the Energy Barriers for Methyl Cation Transfer in the Reactions of Methanol with Protonated Methanol, Protonated Acetonitrile, and Protonated Acetaldehyde: A Low Pressure FTICR Study
作者:Travis D. Fridgen、Jonathan D. Keller、Terry B. McMahon
DOI:10.1021/jp0043165
日期:2001.4.1
The enthalpies of activation were determined to be -16.9 ( 0.6, -16.5 ( 0.6, and -18.4 ( 0.7 kJ mol -1 for the methanol/protonated methanol, methanol/protonated acetonitrile, and methanol/protonated acetaldehyde reactions, respectively. These values agree quite well with ab initio-calculated values. The entropies of activation were found to be quite similar for all three reactions within experimental
已通过低压 FT-ICR 质谱法对甲醇与质子化甲醇、质子化乙腈和质子化乙醛之间的甲基阳离子转移反应进行了实验研究。在 Arrhenius 型分析中确定这些反应的速率常数的温度依赖性,以获得活化能、焓和活化熵。对于甲醇/质子化甲醇、甲醇/质子化乙腈和甲醇/质子化乙醛反应,活化焓分别确定为 -16.9 ( 0.6、-16.5 ( 0.6 和 -18.4 ( 0.7 kJ mol -1 )。这些值与从头计算的值非常吻合。在实验不确定性内,所有三种反应的活化熵都非常相似,这是预期的,因为所有反应的过渡态结构相似。报告了三种反应在 MP2/6-311G** 水平和基组下计算的从头算势能表面。对于甲醇/质子化乙腈和甲醇/质子化乙醛反应,建议在甲基阳离子转移之前将最初产生的质子结合二聚体异构化为甲基结合复合物。预计第一次异构化的屏障明显低于甲基阳离子转移的屏障,因此它不会干扰后者的实验测定。对于甲醇/质