Absorption spectra and reaction kinetics of the radical anion, radical cation and OH adduct(s) of 3,5‐dinitroanisole studied by pulse radiolysis

Abstract

AbstractPulse radiolysis of an aqueous solution of 3,5‐dinitroanisole (dNA) containing 0.1 mol dm−3 isopropanol results in the formation of the radical anion of dNA by attachment of solvated electrons with a rate constant of 4.2 × 1010 dm3 mol−1 s−1 and by reaction of dNA with the isopropanol radical, (CH3)2COH, with a rate constant of 2.5 × 109 dm3 mol−1 s−1. The absorption spectrum of dNA− is characterised by a maximum at approximately 275 nm (ϵ,≈︁14 × 103 dm3 mol−1 cm−1) with shoulders at 300 nm and 410 nm. The extinction coefficient is less than 100 dm3 mol−1 cm−1 in the wavelength region 500 nm to 600 nm. The anion decays by a second order process the rate of which decreases with increasing pH.Reaction of OH radicals with dNA in an aqueous solution occurs with a rate constant of 4 × 109 dm3 mol−1 s−1 and results in an absorption in the visible region. The absorption can be separated into two components with maxima at 470 nm and 515 nm on the basis of differing decay kinetics at different wavelengths. The absorption with γmax = 470 nm has an additional band which increases into the infra red and is assigned to a complex between the OH radical and the π‐electron system of dNA. The absorption with γmax = 515 nm is assigned to a combination of the four possible cyclohexadienyl type radicals which can result from σ‐bond formation between OH and a ring carbon atom.An absorption with γmax = 480 nm, found on pulse irradiation of a deaerated solution of dNA in cyclohexane, is attributed to the radical cation of dNA. The extinction coefficient of dNA+ is estimated to be 6.0 + 0.6 × 103 dm3 mol−1 cm−1.