A ring-strain model for predicting 29Si NMR chemical shifts in polyhedral oligomeric silsesquioxanes and siloxanes

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.