A THEORETICAL REVISIT ON 2-NORBORNYL CATION

Abstract

The 2-norbornyl cation is an old topic in physical-organic chemistry. Whether in classical or non-classical form (partial bridged form) it has been one of the focus of discussion. Currently the experimental data and theoretical calculations favorably support the idea that 2-norbornyl cation is not in the classical form in the stable-ion condition. In this paper, first, we will show that a 3-center-2-electron π-complex is formed by the collapse of 2-norbornyl cation. Further, using different theoretical methods (B3LYP, MP2) with different basis sets (6-31+ G , 6-31 G (d,p), 6-311 G (d,p), 6-311 G (2d,p)), we find that there is a trend for the 3-center-2-electron π-complex to approach the Cs symmetry, and this π-complex oscillates within the numerical limits of the perfect Cs symmetrical configuration. The stabilization energies of the π-complex are 13.87 Kcal/mol and 19.47 Kcal/mol by B3LYP/6-31+G and MP2/6-31+G, respectively. Second, our calculations also show that the transition state between 2-norbornyl cation and 3-norbornyl cation is formed by a 3, 2-proton shift, not the generally accepted 3, 2-hydride shift. The activation energy of this 3, 2-proton shift is 10.9 Kcal/mol. Detailed structural changes in the optimization process and the formation of transition state (also a 3-center-2-electron π-complex) between 2-norbornyl cation and 3-norbornyl cation will also be included.