Fusaro Luca, Mameli Giulia, Mocci Francesca, Luhmer Michel, Cerioni Giovanni
Laboratoire de Résonance Magnétique Nucléaire Haute Résolution CP 160/08, Université Libre de Bruxelles, Bruxelles, Belgium.
Magn Reson Chem. 2012 Feb;50(2):152-8. doi: 10.1002/mrc.3794. Epub 2012 Feb 28.
(17)O NMR is not routinely used for structure characterization, and kinetic studies of fluxional organic compounds are seldom undertaken because poor sensitivity and fast quadrupole relaxation are frequently regarded as intractable issues. This work shows how, nowadays, quantitative (17)O dynamic NMR studies on small organic molecules are feasible without enrichment being needed. It reports on acetoxysilanes, a class of fluxional compounds whose structure and dynamics were to be clarified. Natural abundance (17)O NMR spectra were recorded over a wide range of temperatures using standard instrumentation. The analysis relies on simple linewidth measurements and directly provides the activation parameters. The activation enthalpy is found to decrease with increasing number of acetoxy groups bound to silicon. Density functional theory calculations properly predict this trend and show that a single oxygen atom of the acetoxy group is bound to silicon, excluding chelation as binding mode, and that the dynamic process involves the shift of the silicon atom between the two oxygen atoms of the acetoxy group.
（17）O核磁共振通常不用于结构表征，并且很少对易变有机化合物进行动力学研究，因为灵敏度低和四极弛豫快常常被视为棘手的问题。这项工作展示了如今如何在无需富集的情况下对小分子有机化合物进行定量（17）O动态核磁共振研究。它报道了乙酰氧基硅烷，这是一类结构和动力学有待阐明的易变化合物。使用标准仪器在很宽的温度范围内记录了天然丰度（17）O核磁共振谱。分析依赖于简单的线宽测量，并直接提供活化参数。发现活化焓随着与硅相连的乙酰氧基数量的增加而降低。密度泛函理论计算正确地预测了这一趋势，并表明乙酰氧基的单个氧原子与硅相连，排除了螯合作为结合模式，并且动态过程涉及硅原子在乙酰氧基的两个氧原子之间的移动。
