Comparison of hydrogen atom and hydroxyl radical reactions with simple aromatic molecules in aqueous solution

• Published in: Chemical physics Vol. 534; p. 110754
• Main Authors: Homlok, Renáta, Mile, Viktória, Takács, Erzsébet, Járvás, Gábor, Góger, Szabolcs, Wojnárovits, László
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2020
• Subjects: Cyclohexadienyl radical; Hydrogen atom; Hydroxyl radical; Radical addition; Spectral calculations; Hydrogen atom; Spectral calculations; Radical addition; Hydroxyl radical; Cyclohexadienyl radical
• ISSN: 0301-0104
• DOI: 10.1016/j.chemphys.2020.110754

[Display omitted] •Main reaction of H and OH with simple aromatic molecules is addition to the ring.•Ortho and para reactions are favoured independently of the nature of substituent.•Meta and ipso reactions are disfavoured.•In chloro-, bromo- and nitrobenzene direct substituent elimination also takes place.•The OH adduct of anilinium ion undergoes fast water elimination.•In benzylchloride OH adds to the ring, H abstracts H-atom from the side chain. The reactions of hydrogen atoms and hydroxyl radicals with benzene and 10 monosubstituted benzenes were investigated by measuring transient absorption spectra, calculating Gibbs free energies, absorption spectra of intermediates formed and determining the rate constants of H reactions. The basic reaction is addition to the aromatic ring forming cyclohexadienyl type radicals. Most radical exhibit absorption spectra with maxima in the 300–340 nm range, these maxima for molecules with strong electron withdrawing groups are shifted to 340–420 nm. The spectra of H and OH adducts are similar suggesting similar intermediates. In substituted benzenes the absorption band is due to several isomers. Ortho and para additions are important in reaction with all molecules studied. Both, H and OH can react with the –Cl, –Br and –NO2 substituents in exchange reaction without cyclohexadienyl radical. OH reacts with the aromatic ring of benzyl chloride in radical addition, while H eliminates Cl from the substituent.