CRYSTAL AND MOLECULAR-STRUCTURES OF PYRYLIUM-SALTS .3. CRYSTAL AND MOLECULAR-STRUCTURE OF 2,6-DIPHENYL-4-(4-N,N-DIMETHYLAMINOPHENYL) PYRYLIUM PERCHLORATE - A CASE OF A LONG-DISTANCE SUBSTITUENT EFFECT ON GEOMETRY OF THE PYRYLIUM RING

The crystal and molecular structure of 2,6-diphenyl-4-(4-N,N-dimethylaminophenyl)pyrylium perchlorate has been determined by X-ray diffraction methods given R = 0.061 and mean esd for bond lengths 0.006 angstrom and bond angles 0.3-degrees. NMe2-substitution in the para position causes a strong through-resonance effect with the positively charged pyrylium ring. As a result, (i) a shortening of internal bond length with maintaining coplanarity, and (ii) a decrease of aromatic character of the pyrylium ring due to localization of two pi-CC bonds, are observed.