Thermodynamic stability of trichlorocyclopropenyl cation. An experimental (FTICR) and computational [G2(MP2)] study

The standard Gibbs energy change for the halide transfer between tert-butyl chloride and trichlorocyclopropenyl cation has been determined by means of Fourier transform ion cyclotron resonance mass spectrometry. Trichlorocycl opropenyl cation is found to be substantially more stable than tert-butyl a nd l-adamantyl cations. This reaction and cognate processes were also studi ed at the ab initio G2(MP2) level. The agreement between experimental and c alculated changes of thermodynamic state functions is remarkably good. On t he basis of these results, isodesmic and homodesmotic reactions were constr ucted. They led to the delocalization energy in 1 and to the quantitative a ssessment of substituent effects on the stability of the aromatic 2 pi-elec tron system.