A comparative study by AM1, PM3 and ab initio HF/3-21G methods on the structure and reactivity of monosubstituted carbanion 1,2,4-triazolium ylides

A full conformational analysis of six 1,2,4-monosubstituted carbanion 1,2,4 -triazolium ylides 4 a-f was performed using AM1,PM3 and HF/3-21G methods. The C-type conformers were found as the most stable structures by these dif ferent methods. This study also includes a qualitative estimation of the ch emical behavior of triazolium ylides 4 a-f as nucleophilic agents on the le vel of ylide carbon atoms. The ab initio 3-21G method seems to be the most suitable in the characterization of these molecular systems. (C) 2000 Elsev ier Science B.V, All rights reserved.