13C and 2H Kinetic Isotope Effects and the Mechanism of Bromination of 1-Pentene under Synthetic Conditions

The 13C and 2H kinetic isotope effects for the bromination of 1-pentene with Br2 in CCl4 were determined and interpreted with the aid of calculationally predicted isotope effects. The isotope effects observed are consistent with rate-limiting bromonium ion formation and do not fit with either rate-limiting production of a π complex or reaction of a reversibly formed bromonium ion. This rules out some of the mechanistic complexities suggested for other brominations, though the identity of the brominating reagent(s) under these synthetic conditions remains uncertain.