Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5417209 | Journal of Molecular Structure: THEOCHEM | 2009 | 8 Pages |
Abstract
The competitive reaction paths (Scheme 1) for the carbo and hetero Diels-Alder reaction of E-2-phenyl-1-cyano-1-nitroethene (1) to cyclopentadiene (2) were examined using the B3LYP exchange-correlation functional and the 6-31G(d) basis set. The calculated activation enthalpies indicate that preference of the paths increases in the order: AÂ =Â CÂ >Â BÂ >Â DÂ >Â FÂ >Â E. In the gas phase, all reactions occur via pre-reaction complexes, which on the paths A, B, C and E resemble orientation complexes. On path A the initially formed 2-phenyl-3-cyano-4-aza-5-oxy-bicyclo-[3,4,0]-nona-3,7-diene N-oxide (5) is converted to endo-nitronorbornene 3 as a result of a [3.3]-sigmatropic shift. On path B, which yields exo-nitronorbornene 4, and pathways C-F, which yield 2-phenyl-3-cyano-4-aza-5-oxy-bicyclo-[3,4,0]-nonadienes N-oxides 6-8, the reaction proceeds according to a concerted mechanism. When a solvent is introduced into the reaction environment, activation barriers are slightly reduced and the degree of formation of new Ï-bonds in transition structures is lowered. The solvent effect however is not sufficient to induce a change of the reaction mechanism or the reaction path preference. The global electrophilicity and electron chemical potential of the reagents 1 and 2 harmonise with the data of the B3LYP/6-31G(d) simulations.
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Authors
R. JasiÅski, M. Kwiatkowska, A. BaraÅski,