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Paper | Regular issue | Vol 32, No. 8, 1991, pp.1547-1557
Published online, 1st January, 1970
DOI: 10.3987/COM-91-5755
Heterocyclic Rearrangements. A Semiempirical Study of a Degenerate Rearrangement in the 1,2,4-Oxadiazole Series

Gianfranco La Manna, Silvestre Buscemi, Vincenzo Frenna, Nicolò Vivona,* and Domenico Spinelli

*Dipartimento di Chimica Organica, Università digli Studi di Palermo, Via Archirafi 20 90123 Palermo, Italy

Abstract

A semiempirical approach to the rearrangement of the 3-acetylamino-5-methyl-1,2,4-oxadiazole is reported. Quantum mechanical calculations at the MNDO and AM1 level have been carried out for the anionic form of the acetylaminooxadiazole and for the transition state. The theoretical value of activation energy for the degenerate process has been compared with the experimental free energy of activation previously obtained by the dynamic 1H-nmr. The calculations have been also extended to the different conformers of the anionic acetylamino moiety and to the conformational processes. Furthermore, a quasi-degenerate rearrangement for the 3-trideuterioacetylamino-5-methyl-1,2,4-oxadiazole has been pointed out by nmr technique, and the calculated free energy of activation confirmed the expected lower reactivity of the neutral species with respect to the anionic one.