A Ring-Strain Model for Predicting 29Si NMR Chemical Shifts in Polyhedral Oligomeric Silsesquioxanes and Siloxanes

Abstract

We present a model for predicting ²⁹Si NMR chemical shifts (δ) in polyhedral oligomeric silsesquioxanes (POSS) and siloxanes (POS) incorporating rings with 3, 4, 5 and/or 6 Si atoms. The model, based on the ²⁹Si NMR spectra of POSS/POS compounds with 30 different functional groups, relies on the observation that the influence of ring strain on δ is essentially independent of the functional group attached to the polyhedra. It is anticipated that such correlations would be of value in attributing ²⁹Si NMR chemical shifts in new POSS and POS compounds