(eta(1)-5-Chloropentene)pentacarbonylchromium(0), (eta(1)-ol-Cl)Cr(CO)(5), 1, and (eta(2)-5-chloropentene)pentacarbonylchromium(0), (eta(2)-Cl-ol)Cr(CO)(5), 2, respectively, in which 5-chlorobenzene is bonded to Cr via a lone pair on chlorine or through the olefinic linkage, respectively, are produced via pulsed laser flash photolysis of Cr(CO)(6)/ Cl-ol solutions. Compound 1 then isomerizes to 2 on the submillisecond time scale. This process has been monitored both by IR and visible spectrophotometry by employing fluorobenzene (FB) as an inert diluent. Parallel studies of flash photolysis of Cr(CO)(6) in solutions containing 1-chlorobutane and 1-hexene, both neat and diluted with FB, where the Cl and ol functional groups are not linked, also were carried out. The data support a dissociative isomerization mechanism involving rate-determining Cr-Cl bond breaking. Activation parameters for this process have been obtained. The accessibility of a proposed low-energy pathway involving "agostic" C-H-Cr interactions in the transition state is evaluated.