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

Molecular structure and conformational flexibility of Meisenheimer complexe s of 5,7-dinitroquinoline derivatives are studied experimentally using X-ra y diffraction and theoretically by semi-empirical AMI calculations. The dih ydrocycle is found to possess high conformational flexibility in all anioni c sigma-complexes considered. Substituent steric effects at the saturated c arbon atom of the anion significantly influence the equilibrium conformatio n and deformability of the partially hydrogenated ring. An increase of the bending strain does not cause considerable changes of the conformational ch aracteristics of ring. In the crystal phase, the geometry of the anion depe nds essentially on the crystal structure and on the cation coordination. (C ) 2000 Elsevier Science B.V. All rights reserved.