Computational determination of the relative stabilities of some nitro carbocations

The relative stabilities of a group of nitro carbocations (derivatives of the methyl, cyclopropyl, and cyclopropenyl cations) are determined by means of abinitio SCF/3-21G calculations, and compared to the corresponding results for other substituent groups, both electron donating and withdrawing. The α-nitro carbocations are generally destabilized relative to the parent cation, but often to a lesser extent than anticipated from the strongly electron-withdrawing nature of NO 2 . The optimized structures indicate that this is due to the stabilizing formation of an intramolecular ring involving the nitro group; however, this requires the proximity of a sufficiently positive carbon. Keywords: carbocations, abinitio SCF calculations, relative stabilities, nitro derivatives.