Substituent steric effects and molecular structure of anionic σ-complexes of 5,7-dinitroquinoline

Abstract

Molecular structure and conformational flexibility of Meisenheimer complexes of 5,7-dinitroquinoline derivatives are studied experimentally using X-ray diffraction and theoretically by semi-empirical AM1 calculations. The dihydrocycle is found to possess high conformational flexibility in all anionic σ-complexes considered. Substituent steric effects at the saturated carbon atom of the anion significantly influence the equilibrium conformation and deformability of the partially hydrogenated ring. An increase of the bending strain does not cause considerable changes of the conformational characteristics of ring. In the crystal phase, the geometry of the anion depends essentially on the crystal structure and on the cation coordination.