10.1021/jo00314a010
The research investigates the dynamic equilibria between pentavalent protonated oxyphosphoranes and their isomeric tetravalent enol phosphonium ions through inter- and intramolecular proton transfer, using low-temperature NMR measurements. Key chemicals involved include several pentavalent oxyphosphoranes, fluorosulfonic acid (FS03H), and methoxy groups. The study reveals that rapid equilibria can be achieved by imposing certain structural constraints on the system, reducing the entropy expenditure required for the rigid closed form of the protonated oxyphosphorane. In one case, evidence for an intramolecular proton-exchange process controlled by an intermediary pentavalent protonated oxyphosphorane is presented. The findings provide insights into intramolecular phosphorylation processes relevant to biological systems and highlight the role of protonated pentacoordinated phosphorus intermediates in various biochemical reactions.