Dynamic NMR of low-sensitivity fast-relaxing nuclei: 17O NMR and DFT study of acetoxysilanes.

17O NMR is not routinely used for structure characterization, and kinetic studies of fluxional org. compds. are seldom undertaken because poor sensitivity and fast quadrupole relaxation are frequently regarded as intractable issues. This work shows how, nowadays, quant. 17O dynamic NMR studies on small org. mols. are feasible without enrichment being needed. It reports on acetoxysilanes, a class of fluxional compds. whose structure and dynamics were to be clarified. Natural abundance 17O NMR spectra were recorded over a wide range of temps. using std. instrumentation. The anal. relies on simple linewidth measurements and directly provides the activation parameters. The activation enthalpy decreases with increasing no. of acetoxy groups bound to Si. D. functional theory calcns. properly predict this trend and show that a single O atom of the acetoxy group is bound to Si, excluding chelation as binding mode, and that the dynamic process involves the shift of the Si atom between the two O atoms of the acetoxy group. Copyright © 2012 John Wiley and Sons, Ltd. [on SciFinder(R)]