selectively substituted naphthalenetricarbonylchromium complexes are heated the tricarbonylchromium groups are redistributed between the substituted and the unsubstituted rings because of inter-ring haptotropic rearrangements. The rate constants of these isomerizations were measured. During rearrangement of individual isomers of (1-methylacenaphthene)tricarbonylchromium the configuration of the methyl group