%0 Journal Article %A Stevens, John %A Schweizer, Marcus %A Rauhut, Guntram %D 2001 %T Toward an Understanding of the Furoxan−Dinitrosoethylene Equilibrium %U https://acs.figshare.com/articles/journal_contribution/Toward_an_Understanding_of_the_Furoxan_Dinitrosoethylene_Equilibrium/3634473 %R 10.1021/ja010792c.s001 %2 https://acs.figshare.com/ndownloader/files/5723223 %K ci %K dinitrosoethylene %K transition state %K singlet pathway %K transition states %K alternative routes %K nitroso groups %K T 1 surfaces %K perturbational methods %K S 0 %K benzofuroxan %K Model potentials %K density functionals %X The tautomerism of furoxan (1,2,5-oxadiazole-2-oxide) has been investigated by different computational methods comprising modern density functionals as well as single-reference and multi-reference ab initio methods. The ring-opening process to 1,2-dinitrosoethylene is the most critical step of the reaction and cannot be treated reliably by low-level computations. The existence of ciscistrans-1,2-dinitrosoethylene as a stable intermediate is advocated by perturbational methods, but high-level coupled-cluster calculations identify this as an artifact. In contrast to the analogous reaction in benzofuroxans, cisciscis-1,2-dinitrosoethylene was found to be a transition state rather than a local minimum. Model potentials were used to explain the occurrence and the disappearing of transition states and local minima relative to the reaction of benzofuroxan. Low-lying triplet states that can be accessed due to spin−orbit coupling were investigated as taking part in alternative routes to a proposed singlet pathway. Barriers for rotations of the nitroso groups on the S0 and T1 surfaces are reported. %I ACS Publications