An IR study of the interaction between pyridine and iodine

Molecular Complexes in the Liquid-phase Halogenation of Unsaturated Compounds

“…Complex formation explains negative activation energies in radical bromination, since the enthalpy of formation of the radical-complex occurs in the activation energy with a negative sign 116 . A negative activation energy due to reversible formation of a bromoalkyl radical has been reported for the gas-phase hydrobromination of alkenes 151 .…”