Solvolysis of 1,3-di-tert-butyl-5-methyl-5-cyclopenta-1,3-dienyl trifluoroacetate (15a) occurs with a strong dependence on solvent ionizing power (m = 0.97), and gives products of substitution, allylic and skeletal rearrangement with substitution, and elimination. These results are characteristic of a process involving an intermediate carbocation, and provide the first measurements of the kinetics of formation of a cyclopentadienyl cation, the prototypical 4π-electron carbocation destabilized by antiaromaticity. The reactivity of 15a in 2,2,2-trifluoroethanol at 25 °C is calculated to be lower than those of analogous fluorenyl and indenyl derivatives by factors of 3 × 104 and 4 × 102, and is exceeded by that calculated for 1,3-dimethyl-3-cyclopentenyl trifluoroacetate by a factor of 1014, showing the large carbocation destabilizing effects of antiaromaticity.

1996 magnetic resonance, nuclear quadrupole resonance magnetic resonance, nuclear quadrupole resonance (organic substances) K 2560 26 -036 13C, 17O, and 29Si NMR Spectra and Stabilization of Silylated Ketenes and Bisketenes. -The stabilizing influence of silyl substituents on ketenes and bisketenes is discussed. The electronic distributions in these molecules are examined by means of NMR spectroscopy. -(ALLEN, A. D.; EGLE, I.; JANOSCHEK, R.; LIU, H. W.; MA, J.; MARRA, R. M.; TIDWELL, T. T.; Chem. Lett. (1996) 1, 45-46; Dep. Chem., Univ. Toronto, Toronto, Ont. M5S 1A1, Can.; EN)