Mixtures, of phenanthrene (P) and hydrophenanthrenes (HI's) of increasing hydrogenation degree (H2P, H4P, H(8)Ps, H14PS) were obtained by hydrogenation of P under kinetic control conditions on Ni catalyst at 292 degreesC and 315 degreesC under constant hydrogen pressure (7.1-7.8 MPa) for reaction times up to 96 min, Thermal treatments (400 degreesC, 60 min) of the final mixtures have permitted to define the roles of individual molecular species (in particular H2P and s-H8P) in bimolecular reactions of H-exchange and disproportionation and in unimolecular reactions of isomerization and fragmentation connected to the thermal dehydrogenation. H(8)Ps, as overhydrogenated donor species, were further examined with regard to the bimolecular reactions at higher temperature (484 degreesC) and shorter reaction times (10 min) in the presence of P added as coal model. (C) 2002 Elsevier Science B.V All rights reserved.