Photochemistry studied with ab initio orbital-correlation and state-correlation plots: Classic cyclobutene ring opening, and the reaction of N2 with photoexcited O2

Huancong Shi; David C Roettger; Allan L L East

doi:10.1002/jcc.20843

Photochemistry studied with ab initio orbital-correlation and state-correlation plots: Classic cyclobutene ring opening, and the reaction of N2 with photoexcited O2

J Comput Chem. 2008 Apr 30;29(6):883-91. doi: 10.1002/jcc.20843.

Authors

Huancong Shi¹, David C Roettger, Allan L L East

Affiliation

¹ Department of Chemistry and Biochemistry, University of Regina, Regina, Saskatchewan S4S 0A2, Canada.

PMID: 17963232
DOI: 10.1002/jcc.20843

Abstract

Pericyclic reaction theory arose from ideas presented in 1965, based on orbital-energy correlation diagrams (Woodward and Hoffmann) and state-energy correlation diagrams (Longuet-Higgins and Abrahamson). Here we have used ab initio complete-active-space self-consistent field (CASSCF) calculations to generate such diagrams. First we present diagrams for the classic case of cyclobutene ring opening, to demonstrate agreement between the CASSCF results and the classic diagrams of both Woodward/Hoffmann and Longuet-Higgins/Abrahamson. Then we present diagrams for the more difficult cases of N(2) + photoexcited O(2), to produce either 2 NO or NNO + O. These N(2) + O(2) cases feature significant electron reorganization, for which elementary pencil-and-paper diagrams are less accurate. Finally, the benefits and limitations of such diagrams for predicting photochemistry are briefly discussed.