Charge-transfer complexes of bromine atoms with haloalkanes and alkanes

Charge-transfer complexes of bromine atoms with haloalkanes and alkanes were produced by pulse radiolysis and by laser-flash photolysis in various organic solvents. Br atoms were produced by photolysis of Br₂ (at 351 or 248 nm), by photolysis of bromoalkanes (at 248 nm), or by radiolysis of bromoalkanes (either in liquid form or in cyclohexane solutions). The transient spectra, monitored within microseconds after the pulse, had absorption maxima that varied between 300 and 500 nm and are ascribed to complexes of Br atoms with the various solvents or other solutes present. The absorption maxima for Br atom complexes with alkanes and chloroalkanes correlate with the ionization potential of these molecules, suggesting the existence of charge-transfer complexes. The correlation for the bromoalkanes was more complex. CBr₄·Br and CHBr₃·Br were observed to react rapidly (k = 10⁸-10⁹ L mol^-1 s^-1) with Br₂ and with HBr to transfer their Br atom to these latter molecules.