Studying the hydrogen atom position in the strong-short intermolecular hydrogen bond of pure and 5-substituted 9-hydroxyphenalenones by invariom refinement and ONIOM cluster computations

Abstract

Abstract The solid-state structures of three H-bonded enol forms of 5-substituted 9-hydroxyphenalenones were investigated to accurately determine the H atom positions of the intramolecular hydrogen bond. For this purpose, single-crystal X-ray diffraction (SC-XRD) data were evaluated by invariom-model refinement. In addition, QM/MM computations of central molecules in their crystal environment show that results of an earlier standard independent atom model refinement, which pointed to the presence of a resonance-assisted hydrogen bond in unsubstituted 9-hydroxyphenalone, are misleading: in all our three and the earlier solid-state structures the lowest energy form is that of an asymmetric hydrogen bond (CS form). Apparent differences of results from SC-XRD and other analytical methods are explained.