Table I shows the activation parameters found for the thermolysis of cyclobutene and substituted cyclobutenes, including 1 1 new examples. Thermolysis of the labile 3- ethoxycyclobutene was carried out at 30-50 OC, and the reaction was followed by UV in hexane or by NMR in CC14 solution. All other data are for gas-phase reactions, which were followed by GC analysis. As shown in Table I, substitution mainly influences the activation ...