Thermal isomerizations of trimethylcyclopentadienes

The title reaction was studied in gas phase in a microreactor with residence times of 5-50 sec. and the products studied by their spectral data and their hydrogenation products. On heating 1,5,5-trimethylcyclopenta-1,3-diene at 350-400 Deg, it gave 1,2,3-trimethylcyclopenta-1,3-diene (I), 1,2,3-trimethylcyclopenta-2,4-diene, and 1,2,3-trimethylcyclopenta-3,5-diene by 1st-order kinetics (H.dbldag. = 40.3 kcal./mole and S.dbldag.= -4 cal./degree, mole). Similarly, 2,5,5-trimethylcyclopenta-1,3-diene gave I (H.dbldag. = 44.4 kcal./mole and S.dbldag. = 3 cal./degree mole) and 1,2,4-trimethylcyclopenta-2,4-diene (II) (H.dbldag. = 44.2 kcal./mole and S.dbldag. = 6 cal./degree mole). At higher temps., I as well as II yielded mixts. of I and II. A possible mechanism of the reaction was suggested. [on SciFinder (R)