Etude MNDO des composes conjugues enneagonaux

We present MNDO calculations of a series of nine‐membered conjugated compounds. The geometries have been fully optimized. Cyclononatetraenyl and benzocyclononatetraenyl anions, nonapyrrol, and nonathiophene appear to be planar aromatic compounds. Following MNDO , nonafulvene has a planar prefered conformation, but a polyenic structure, while nonafuran and cyclononatetraene are gauche molecules. The Universal Huckel Method ( UHM ), a simple all valence electron empirical technique which describes σ systems using localized MO , gives, qualitatively, the same results as the MNDO method. The quantum calculation carried out with MNDO and UHM have been used to describe the physicochemical properties of ninememberedring conjugated compounds under consideration. To our knowledge, we present here the first theoretical study dealing with nine‐membered conjugated molecules.