Department of Chemistry, Texas A&M University, College Station, Texas 77842, USA.
J Am Chem Soc. 2010 Sep 15;132(36):12548-9. doi: 10.1021/ja1055593.
The intramolecular (13)C kinetic isotope effects for the ring-opening of cyclopropylcarbinyl radical were determined over a broad temperature range. The observed isotope effects are unprecedentedly large, ranging from 1.062 at 80 degrees C to 1.163 at -100 degrees C. Semiclassical calculations employing canonical variational transition-state theory drastically underpredict the observed isotope effects, but the predicted isotope effects including tunneling by a small-curvature tunneling model match well with experiment. These results and a curvature in the Arrhenius plot of the isotope effects support the recently predicted importance of heavy-atom tunneling in cyclopropylcarbinyl ring-opening.
在较宽的温度范围内测定了环丙基卡宾自由基开环的分子内（13）C 动力学同位素效应。观察到的同位素效应是前所未有的大，范围从 80°C 的 1.062 到-100°C 的 1.163。采用正则变分过渡态理论的半经典计算严重低估了观察到的同位素效应，但包括小曲率隧道模型的隧道作用在内的预测同位素效应与实验吻合较好。这些结果和同位素效应的阿伦尼乌斯图的曲率支持了最近预测的重原子隧道在环丙基卡宾环开环中的重要性。
