Synthesis, crystal structure, and dielectric constants of 9-hydroxy-5-iodophenalen-1-one and its deuteroxy analogue Original Research Article

A large deuterium isotope effect on the temperature dependence of the dielectric responses of 9-hydroxy-5-iodophenalen-1-one (IHP) has been revealed by dielectric constant measurements. The dielectric constant of IHP is almost temperature independent, while that of 9-deuteroxy-5-iodophenalen-1-one (IDP) exhibits a peak at 40 K with a shoulder at around 25 K. The anomalies in IDP are interpreted as successive phase transitions accompanying the ordering of tautomerization. The crystal structure of IHP has been determined and found to be isomorphic to the 5-bromo analogue. Double-minima electron density for the tunneling proton was revealed from the difference-Fourier map.