Spectrophotometric Study of the Intreaction of some Benzo, Benzyl and Phnylcrown Ethers with Pi-Acceptor DDQ in Chloroform Solution

The interaction between benzo-15-crown-5 (B15C5), dibenzo-18-crown-6 (DB18C6), dibenzyl-daza-18crown-6 (DBzDA18C6), N-phenyl-aza-15-crown-5 (NPhA15C5) and dibenzopyridine-18-crown-6 (DBPy18C6) with π-acceptor 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in chloroform solution was studied spectrophotometrically. The interaction of B15C5-DDQ and DB18C6-DDQ caused the formation of 1:1 charge transfer complexes through equilibrium reaction. The interaction of others caused the formation of 1:1 complexes in an equilibrium step and the conversion of the resulting adduct to D+DDQ- (D=NPhA15C5, DBPy18C6, DBzDA18C6) in a nonequilibrium step. The formation constant of DBzDA18C6 was evaluated by computer fitting of the absorbance mole ratio data. Other stability constants were evaluated through the Hildebrand method. It was found that the stabilities vary in the order: B15C5 < DB18C6 < DBPy18C6 < NPhA15C5 < DBzDA18C6. All of the resulting molecular complexes were isolated in crystalline form and characterized.