Vapor phase thermolysis of 5-hexen-1-yn-3-ol affords 2- and 3- cyclopentenecarboxaldehydes, trans 2,5-hexadienal and sorbaldehyde. Since beta-hydroxyolefin cleavage, which normally competes with the oxy-Cope processes, is completely absent, kinetic parameters could be ascertained. Ea and activation entropy of the reaction are indicative of a concerted mechanism and suggest that participation of triple bonds in electrocyclic reactions leads to increased rates in comparison with the corresponding olefinic structures. Based upon kinetic data, upon effects of temperature and contact time on product distribution and upon deuterium tracer studies, a reaction scheme is proposed which centers on the intermediacy of the primary oxy-Cope product. The observed compounds, then, represent various reactions of the allenol, 1-hydroxy-1,2,5-hexatriene. 157th National Meeting of the American Chemical Society, Minneapolis, Minn., April 1969, Abstract # ORGN 105.