Electronic absorption spectra of benzoquinone and its hydroxy substituentsand effect of solvents on their spectra

The electronic absorption spectra of 1,4-benzoquinone (BQ) and its 2,5-dihy droxy and tetrahydroxy derivatives have been studied in detail. The interpr etation of the electronic bands is made on the basis of PPP and CNDO calcul ations. It is found that the pi --> pi* transitions are well predicted by t he PPP method. The predictions of the CNDO method are however superior both in their accuracy as well as ability to predict the n --> pi* transitions. The effect of solvents on the electronic absorption bands have also been i nvestigated in detail. Linear correlations are found between the solvent's dielectric constant and wavelength of the absorption bands. The solvent shi fts are explained on the basis of the polarities of the solute and solvent molecules as well as due to hydrogen bonding. (C) 2000 Elsevier Science B.V . All rights reserved.