Bicyclo[2.1.1]hex-1-yl Cation: an Ab Initio Study of the C6H9+ Potential-Energy Surface

An extensive investigation of the C6H9+ potential-energy surface by ab initio molecular orbital theory is reported. Calculations at the RHF/6-31G* level of theory predict that the bicyclo[2.1.1]hex-1-yl cation (2b) rearranges to the 3-methylenecyclopentyl cation (7b) with an energy barrier of only 0.3 kJ mol-1. Inclusion of electron correlation in the calculation casts doubt on the gas-phase existence of (2b) which is predicted to rearrange without barrier at the MP2/6-31G* level of theory.