Stochastic search for isomers of the sec-butyl cation

摘要

A stochastic search procedure for locating energy minimum structures was applied to the sec- butyl cation. A previously unreported structure 3' with strong H- hyperconjugative stabilization of the carbocation center was found at several levels of theory (HF, B3LYP, and MP2). The theoretical equilibrium isotope effect (EIE) for the monodeutero isotopomer of 3' (K-eq =1.4; t = -130 degrees C) indicates that the new structure is likely to be largely responsible for the experimentally observed EIE.