INFLUENCE OF ONIUM SUBSTITUENT IN PHTHALOYL RING ON THERMODYNAMIC PARAMETERS OF EQUILIBRIUM BETWEEN DIMER AND FREE RADICALS OF 2-(4-DIMETHYLAMINOPHENYL)-1,3-INDANDIONES

Article abstract of DOI:10.1007/BF00957842

2,2'-Bis<2-(4-dimethylaminophenyl)-5-trimethylammonio-1,3-indandione> diperchlorate and 2,2'-bis<2-(4-dimethylaminophenyl)-5-(2,4,6-triphenylpyridinio)-1,3-indandione> diperchlorate have very definite thermochromic and mechanochromic properties, owing to reversible dissociation into free radicals.The rupture energy of the central bond C2-C2' in 5-substituted 2,2'-bis<2-(4-dimethylaminophenyl)-1,3-indandiones> in acetonitrile is 63-75 kJ/mole; in the dimer with the bulky 5-(2,4,6-triphenylpyridinium) substituent, the rupture energy is 51 kJ/mole.The equilibrium constants follow the Hammett equation (? = 1.53, acetonitrile, 293 K).Radicals with onium substituents are thermodynamically the most stable of the arylindandionyl radicals that are thus far known, owing to the significant contribution of electrostatic interactions.