Molecular structure and substituent electronic effects in 10-arylidenanthrones-9

Abstract

X-ray structural studies of derivatives of 10-arylidenanthrone-9 containing π-electron donating and withdrawing substituents within arylidene fragment have been carried out. In the crystal the molecules are strongly disflattened with the central dihydrocycles adopting an asymmetric boat conformation. This geometry of the molecules is a result of unfavourable non-valence interactions between atoms at the C=C bond and the hydrogens at the peri-positions of the anthraquinone fragment. Calculations performed by the semiempirical quantum-chemical AM1 method demonstrate that in the gas phase equilibrium geometry of the molecules was similar to that in the crystal. It was shown as well that the central dihydrocycle possesses high conformational flexibility in spite of steric overcrowding in all of the compounds. Electronic effects of the substituents had significant influence only on the arylidene moiety, resulting in different rotation angles of the phenyl group around the C=C exocyclic bond and virtually no effect on the anthraquinone part of the molecules.