102. “Photo-rearrangement of N-substituted pyridinium and meta-alkoxypyridinium ions”
     Grove, K.; King, R. A.; Burger, U.
     J. Mol. Struct. 2007, 807, 25-32.

A computational study of the minimum-energy structures and transition states relevant to the photo-initiated rearrangement of N-substituted pyridinium and meta-alkoxypyridinium ions is reported. Density Functional Theory in the form of 6-31G(d) B3LYP computations has been used to determine the relative energies of the significant stationary points on the ground state potential energy surfaces, including the global minima, the bicyclic (prefulvene-like) and tricyclic (benzvalene-like) intermediates, and the connecting transition states. The S₀, S₁, and S₂ potential energy surfaces have been mapped along a reaction path from the C_2v-symmetry minimum on S₁ to the bicyclic intermediate on S₀ with multi-reference self-consistent-field computations. Two conical intersections are located along this path, the first occurs as the open-shell electron configuration becomes the ground state, and the second occurs as the closed-shell electron configuration of the bicyclic intermediate becomes the ground state. The impact of various N-substituents on the relative energies of the intermediates is also explored. Previously, experimental X-ray structures have firmly established the exo nature of the photohydration of N-substituted pyridinium and alkylpyridinium ions, however, endosolvation has been claimed for the photoaddition of alcohols to meta-alkoxypyridinium ions. The intermediate structures and energies reported here suggest that exo solvation should also be operative in the case of meta-alkoxypyridinium ions.

DOI : 10.1016/j.theochem.2006.12.001 

archive ouverte unige:7749