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

X-ray structural studies of derivatives of 10-arylidenanthrone-9 containing pi-electron donating and withdrawing substituents within arylidene fragmen t have been carried out. In the crystal the molecules are strongly disflatt ened with the central dihydrocycles adopting an asymmetric boat conformatio n. This geometry of the molecules is a result of unfavourable non-valence i nteractions between atoms at the C=C bond and the hydrogens at the peri-pos itions of the anthraquinone fragment. Calculations performed by the semiemp irical quantum-chemical AM1 method demonstrate that in the gas phase equili brium geometry of the molecules was similar to that in the crystal. It was shown as well that the central dihydrocycle possesses high conformational f lexibility in spite of steric overcrowding in all of the compounds. Electro nic effects of the substituents had significant influence only on the aryli dene moiety, resulting in different rotation angles of the phenyl group aro und the C=C exocyclic bond and virtually no effect on the anthraquinone par t of the molecules.