Heterocyclic Rearrangements. A Semiempirical Study of a Degenerate Rearrangement in the 1,2,4-Oxadiazole Series

A semiempirical approach to the degenerate rearrangement of the 3-acetylamino-5-methyl-1,2,4-oxadiazole is reported. Quantum mechanical calculation 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 1 H-nmr. The calculations have been also extended to the different conformers of the anionic acetylamino moiety and to the conformational processes