Kinetics of the thermal isomerization of 1,1,2-trimethylcyclopropane

✍ Scribed by David K. Lewis; Steven V. Hughes; Justine D. Miller; Jessica Schlier; Kevin A. Wilkinson; Sara R. Wilkinson; Bansi L. Kalra

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 133 KB
• Volume: 38
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20184

✦ Synopsis

Abstract

The Arrhenius parameters for the gas phase, unimolecular structural isomerizations of 1,1,2‐trimethylcyclopropane to three isomeric methylpentenes and two dimethylbutenes have been determined over a wide range of temperatures, 688–1124 K, using both static and shock tube reactors. For the overall loss of reactant, E~a~ = 63.7 (± 0.5) kcal/mol and log~10~ A = 15.28 (± 0.12). These values are higher by 2.6 kcal/mol and 0.7–0.8 than previously reported from experimental work or predicted from thermochemical calculations. E~a~ for the formation of trans‐4‐methyl‐2‐pentene is 1.5 kcal/mol higher than E~a~ for the formation of the cis isomer, which is identical to the E~a~ difference previously reported for the formation of trans‐ and cis‐2‐butene from methylcyclopropane. Substitution of methyl groups for hydrogen atoms on the cyclopropane ring is expected to weaken the CC ring bonds, and it has been reported previously that activation energies for structural isomerizations of methylcyclopropanes do decrease substantially over the series cyclopropane > methylcyclopropane > 1,1‐ or 1,2‐dimethylcyclopropane. However, the present study shows that the trend does not continue beyond dimethylcyclopropane isomerization. Besides reductions in CC bond energy, steric interactions may be increasingly important in determining the energy surface and conformational restrictions near the transition state in isomerizations of the more highly substituted methylcyclopropanes. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 475–482, 2006