The Trishomocyclopropenyl Cation. I. Direct Observation

The trishomocyclopropenyl cation has been prepared for the first time and is shown to be a remarkably stable, highly charge-delocalized species. The large [Formula: see text] value associated with the carbons formally carrying the positive charge, the high-field chemical shift of these carbons, and the absence of hydride shift, all are significant and are consistent with the formulation of 1 subject to the limit of the n.m.r. time scale.

The Trishomocyclopropenyl Cation. II. An Ethano-bridged Derivative

An ethano-bridged trishomocyclopropenyl carbonium ion has been generated in superacid media from 8-chlorotricyclo[3.2.1.02,4]octane and/or 4-chlorotricyclo[3.3.0.02,8]octane. The 1H and 13C n.m.r. spectra of this new stable carbonium ion compare well with those of the parent trishomocyclopropenyl carbonium ion and yet show some indication that the degree of charge delocalization is more extensive than that originally implied.

13C Nuclear Magnetic Resonance Spectra of Bridged 10π-Electron Systems. The Extent of Electron Delocalization

The 13C n.m.r. spectrum of the cation 4 suggests the presence of considerable 1,7-bonding, indicating that it should be described as a substituted homotropylium cation rather than a monocyclic 10π-electron system. The intra-annular carbon atoms of 3 and 4 do not show a significant upfield shift due to the ring current. Explanations are offered.