The vapor phase thermolysis of 5-hexen-1-yn-3-ol affords 2- and 3-cyclopentenecarboxaldehydes, trans-2,5-hexadienal, and sorbaldehyde in varying amts. dependent upon temp. and contact time. Since the beta-hydroxyolefin cleavage, which normally competes with the oxy-Cope processes, is completely absent, kinetic parameters could be detd. The Arrhenius energy of 30+/- 2 kcal/mole and activation entropy of -14eu are indicative of a concerted mechanism and suggest that the particip- ation of triple bonds in electrocyclic reactions leads to increased rates in comparison with the corresponding olefinic structures. The kinetic data obtained the effects of temp. and contact time on product distribution, and the results of a deuterium tracer study indicate the intermediacy of the primary oxy-Cope product in the formation of all obsd. products. The latter, therefore, represent various reactions of the allenol, 1-hydroxy-1,2,5-hexatriene. RCJC Chem Abstr. Vol 72, 131815d.