13C and 2H kinetic isotope effects and the mechanism of bromination of 1-pentene under synthetic conditions

[GRAPHICS] The C-13 and H-2 kinetic isotope effects for the bromination of l-pentene with Br-2 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 pi 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.