Knowledge Bank

The reaction of hydrated proton with p-benzosemiquinone radical, monitored by time-resolved resonance Raman spectroscopy, reveals the spectral features of the anion, neutral and cation forms of the radical in mildly basic to strongly acidic aqueous solutions. In extreme acid solutions, the radical protonates further, to form a dication radical with spectral features similar to that of the hydroquinone cation radical, except that the enhancement of the CH bending (Wilson 9a) mode is severely quenched. The species has been identification as the ring$(\pi )-H+$ bonded hydroquinone cation radical. Application of the vibrational frequency shifts on protonation of the radicals as natural standard for probing chemical interactions will be discussed.