Unusually Stable Vinyl Cations This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie (Ulm). The Frankfurt group thanks Prof. N. Auner for support. We are indebted to Prof. Mark Fink, Tulane University, New Orleans, for carefully reading our manuscript. We thank Thomas Nau, Computer Center Universität Ulm, for adaptation of the Gaussian Program Suite.