Protonated tert-pentyl dication (C5H122+, isopentane dication)

Structures of the tert-pentyl cation (C(5)H(11)(+)) and its protonated dication (C(5)H(12)(2+), isopentane dication) were studied using ab initio methods at the MP2/cc-pVTZ level. Both C-C and C-H hyperconjugatively stabilized structures 1 and 2 , respectively, were found to be minima on the potential energy surface (PES) of the tert-pentyl cation. Structure 1 was computed to be about as stable as structure 2 (slightly more stable by 0.5 kcal mol(-1)). Inter-conversion between 1 and 2 through transition state 3 has a kinetic barrier of only 1.5 kcal mol(-1). The C-H protonated form (H(3)C)(2)C(+)CH(2)CH(4)(+)4 was found to be the global minimum for the protonated tert-pentyl dication. Charges and (13)C NMR chemical shifts of the dication 4 were calculated and compared to those of monocation 1 to study the effect of the additional charge in the dication.