¹H NMR observation of trimethylsilyl migration in gas phase 5-Trimethylsilylcyclopentadiene

Gas-Phase ¹H NMR spectra of a sample containing 4 Torr of trimethylsilylcyclopentadiene, 1 Torr of CHCl₃, and 707 Torr SF₆ show exchange broadened line shapes consistent with the degenerate migration of the trimethylsilyl group in the 5-Isomer via 1-2 sigmatropic shifts. The kinetic parameters for this process in the gas phase, ΔH(+) = 15.4(0.2) kcal mol^-1, ΔS(+) = -1.1(0.1) kcal mol^-1, and ΔG(+) = 15.7 kcal mol^-1 are slightly higher than values reported previously for the neat liquid. The small solvent effect observed indicates that a large charge separation in the transition state is unlikely. (C) 2000 Elsevier Science B.V.