A Computational Study of tert-Butylbenzenium Ions

A computational study of tert-butylbenzenium ions has been performed. Structures and energies of the various isomers and the transition states for their interconversions have been determined. The existence of a stable pi-electron complex (called A1) between a tert-butyl cation and a benzene molecule has been confirmed. Other minimum points on the potential energy surface corresponding to pi-complexes were found, but the barriers for transforming these complexes into the stable pi-electron complex A1 are so low that the transformation into the stable structure can take place at all temperatures. The structures were evaluated at the DFT-B3LYP level of theory. The energies were evaluated with the Gaussian-3 (G3B3) and CBS (CBS-QB3) composite methodologies. A discussion of published experimental data in view of the computational results is given. It is pointed out that it should be possible to show the presence of the pi-complex by IR spectroscopy. The computations show that the pi-complex has a very strong IR band in an otherwise empty region.