The B3LYP, MP2, and CBS-QB3 quantum chemical methods are used to study the relative energy and isomerization reactions of C5H5+ cations. Ease of generation of 14 C5H5+ isomers by ionic dissociation of halide precursors does not correlate well with carbocation stability. The reaction profiles of concerted isomerization of various C5H5+ cations to six select cations are established along with the respective transition states. The rate coefficients of these processes are estimated by using transition state theory and activation energies computed. The transition states for these six reactions are characterized with regard to position along the isomerization pathway as per Hammond's postulate. The 6 isomerization reactions are combined to yield multi-step conversions of various C5H5+ species to the lowest energy vinylcyclopropenyl cation 1. Finally, three different routes for obtaining the select cations from C5H5Br precursors are profiled and the most favored pathways predicted.
Keywords: (C5H5)+ isomers; Carbocation generation; Carbocation isomerization; Carbocation relative energy; DFT; Hammond postulate; MP2.