Potential energy surface of the C3H9+ cations.: Protonated propane

The potential energy surface of the C3H9+ cations was calculated. At the MP4(SDTQ)/6-311++G**/ /MP2(full)/6-31G** level of calculation, structure 4, representing the C-proponium cation, was the lowest in energy, but the van der Waals complex between the isopropyl cation plus hydrogen lies only 0.3 kcal/mol above 4. The results of the calculations are in good agreement with the experimental gas-phase energetic for the reactions involving the C3H9+ species. It was also calculated that the interconversion of the 1-H-proponium cation to the C-proponium cation involves no energy barrier and might be on a pathway explaining the formation of products ascribed to the direct C-C bond protonation in liquid and solid superacids.