title: Dynamic NMR of low-sensitivity fast-relaxing nuclei: (17)O NMR and DFT study of acetoxysilanes.
abstract: (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.
authors.affiliation: Laboratoire de Résonance Magnétique Nucléaire Haute Résolution CP 160/08, Université Libre de Bruxelles, Bruxelles, Belgium.
authors.forename: Luca
authors.initials: L
authors.lastname: Fusaro
authors.forename: Giulia
authors.initials: G
authors.lastname: Mameli
authors.forename: Francesca
authors.initials: F
authors.lastname: Mocci
authors.forename: Michel
authors.initials: M
authors.lastname: Luhmer
authors.forename: Giovanni
authors.initials: G
authors.lastname: Cerioni