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Ab initio study of possible intermediates in the no(4Π) catalyzed geometric isomerizations of olefins

par De Mare, George ;Lantonnois Van Rode, Yves
Référence Research of chemical intermediates, 19, 2, page (131-145)
Publication Publié, 1993

Article révisé par les pairs

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Résumé :

The geometries of acyclic and three-membered ring (nitroxide) H4C2NO radicals in their ground 2Π electronic states have been optimized completely at ab initio UHF and ROHF theoretical levels with the STO-3G and the 6-31G** basis sets. The optimizations favour the cyclic nitroxide structure energetically. However ΔE(acyclic - cyclic) at the UHF and ROHF/6-31G** levels are only 3.2 and 1.9 kcal mol-1, respectively. Incomplete MP2/6-311G** optimizations support these results. The zero-point energy computed at the ROHF/6-31G** level for the nitroxide radical is 2.5 kcal mol-1 higher than that for the acyclic structure, thus reversing the relative energies by 0.6 kcal mol-1. The energies of the two radical structures, relative to the sum of those for ethylene and NO, are very close to literature values of the activation energies for the thermal, NO catalyzed geometrical isomerizations of olefins. Thus cyclic nitroxide intermediates may play a role not only in the Hg 6(3P1) photosensitized, but also in the thermal, NO-catalyzed geometric isomerizations of olefins. © 1993, Springer. All rights reserved.