Antiaromaticity in the parent cyclopentadienyl cation. Reaction of 5-iodocyclopentadiene with silver ion

Advanced Organic Chemistry

“…55 Solvolysis of cyclopentadienyl halides assisted by silver ion is extremely slow, even though the halide is doubly allylic. 56 When the bromide and antimony pentafluoride AROMA TICITY AND ELECTROPHILIC AROMATIC SUBSTITUTION react at -78°C, the product has an EPR spectrum indicating that the cyclopentadienyl cation is a triplet, in agreement with both HMO and more sophisticated MO calculations. 57 The pentachloro derivative is also a triplet, but the pentaphenylcyclopentadienyl cation is a singlet.…”

“…A linear relationship has been demonstrated between the ionization of substituted benzoic acids and the rates of reaction of substituted ethyl arenesulfonates with ethoxide ion in ethano1. 56 In contrast to nucleophilicity, no approach toward specifying leaving-group effectiveness in terms of a single parameter has achieved general acceptance, and it is usual to see such correlations presented as summaries of relative rates. Table 5.8 lists relative rates of solvolysis of 1-phenylethyl esters and halides in 80% aqueous ethanol at 75°C.…”

“…Mixtures of syn and anti addition products are obtained. 56 These reactions also appear to involve a vinyl cation as the dominant intermediate.…”

“…75) nor a strong acid (pKa 11.62), 2-pyridone is an effective catalyst of the reaction of n-butylamine with 4-nitrophenyl acetate. 56 The overall rate is more than 500 times greater when 2-pyridone acts as the catalyst than when a second molecule of butylamine (acting as a general base) is present in the transition state. 2-Pyridone has been called a tautomeric catalyst to emphasize its role in proton transfer.…”

“…Coalescence is also observed between the allylic protons and two of the cyclopropane ring protons. 56 This means 54. E. Vogel, JustusLiebigsAnn.…”