Comparative ab initio and valence electron study of unsaturated 3-membered ring systems. Questions of conjugative and inductive group abilities, of

Abstract

The method of conjugative interruption in conjunction with the CNDO/S and an ab initio method is applied to cyclopropene, cyclopropenone, cyclopropenthione, thiirene 1-oxide, and thiirene 1,1-dioxide. Thereby the orbital interactions between the π orbitals of the CC and M(MCH 2, CO, CS, SO, and SO 2) subunits a quantitatively analyzed as well as their consequences as regards the conjugative and inductive abilities of M, the aromaticities, and geometries of this chemically important series of compounds. A detailed comparison of the CNDO/S and ab initio results is made. Both sorts of calculation yield surprisingly well concurring results. Where the results of both methods basically differ (as to the sign of the aromaticities, or the splitting pattern of two interacting orbitals) it can be traced back to the zero differential overlap approximation made for the valence electron procedure. In addition, the paper presents the first ab initio data on cyclopropenethione, thiirene 1-oxide, and thiirene 1,1-dioxide.