Kinetics of the thermal isomerization of 1,1-dimethylcyclopropane

Rate constants for the unimolecular thermal isomerization of gaseous 1,1-dimethylcyclopropane to isomeric methylbutenes have been measured, and Arrhenius parameters determined, over a wide temperature range, 683–1132 K, using a single-pulse shock tube and a static reactor. For the overall reaction, E<INF>a</INF> = 61.8 ± 0.4 kcal/mol, and log<INF>10</INF>(A, s⁻¹) = 15.04 ± 0.10. These values are in good agreement with previously reported values obtained over a much narrower temperature range. Rate constants for formation of the two major products, 2-methylbut-2-ene and 3-methylbut-1-ene, are given by E<INF>a</INF> = 61.9 kcal/mol, log A = 14.80 and E<INF>a</INF> = 61.1 kcal/mol, log A = 14.54, respectively. A comparison of the activation parameters for structural isomerizations of cyclopropane, methylcyclopropane, and 1,1-dimethylcyclopropane confirms a trend toward lower activation energy values as hydrogen atoms in cyclopropane are replaced by CH<INF>3</INF> groups. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 853–858, 2001