DISORDER DYNAMICS IN SOLID 9-HYDROXYPHENALENONE

H-1 nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation data as well as H-1 decoupled C-13 spectra have been utilized to study the dynamics of the molecular disorder in solid 9-hydroxyphenalenone. In the room-temperature phase-stable between 255 and 380 K-the proton spectrum is narrowed compared to the spectrum of a static structure. This is consistent with a dynamically disordered structure where one of the two nonequivalent molecules reorients rapidly between its two possible equilibrium orientations. The proton spin-lattice relaxation has a maximum of 7.2 s-1 in the same phase at about 355 K, in close agreement with a value of 7.6 s-1 calculated from the dynamical disorder model. The H-1 decoupled C-13 powder spectrum in the room-temperature phase is also consistent with this picture. Above the 385 K phase transition, the C-13 powder spectrum is approaching axial symmetry, proving that all molecules reorient rapidly in that phase.