Thionitroso or thiazyl? Density functional studies of relative stabilitiesbetween the two structural isomers

Density functional calculations (B3LYP/6-31G*) have been performed in order to determine the energies of a series of thionitroso molecules (R-N=S), an d their structural isomers, the thiazyl molecules (R-S dropN). Our computat ional results show that, in general, the thionitroso form is thermodynamica lly more stable than its thiazyl counterpart, except for compounds where th e bonding atom in R is highly electron-withdrawing. However, in all cases, both forms are stationary points on the potential energy surface, regardles s of the higher energies of the less stable isomers. A simple correlation b etween the electronegativity of the bonding atom in R, and the size of the relative stability between the two isomers is established, and presented. F rontier molecular orbital theory is used to successfully account for this c orrelation as well as predict the preferred connectivity. (C) 2001 Elsevier Science B.V. All rights reserved.