Kinetics and mechanism of concurrent bromo-de-protonation and bromo-de-tert-butylation of 1,3,5-tri-tert-butylbenzene at different bromine concentrations were studied experimentally and theoretically. Both reactions have high order in bromine (experimental kinetic orders ~5 and ~7, respectively). According to quantum chemical calculations, such high reaction orders are caused by participation of clustered polybromide anions Br2n-1â in transition states. Bromo-de-tert-butylation has higher order due to its bigger reaction center demanding clusters of extended size.