Correlation of excited-state acidity constants of 2,4-dinitrophenylhydrazones of substituted acetylfluorenes and acetylbiphenyls

Abstract

The excited-state acidity constants, pK*, of several 2,4-dinitrophenylhydrazones of 7-substituted 2-acetylfluorenes and 4′-substituted 4-acetylbiphenyls have been determined in dioxane–water (50% v/v) at 30 °C employing the Förster cycle. The pK* values are correlated with the Hammett σ_p constants. Exalted σ constants are required for –K substituents in fluorene system for a better correlation. The interplanar angle between the planes of the phenyl rings in biphenyl system has been evaluated from the pK* values and found to be 36°.