The gas-phase elimination of several ω-bromonitriles (ZCH 2CH2Br, Z = NC, NCCH2, NCCH2CH 2) has been examined at the MP2/6-31G(d,p), MP2/6-31G(2d,2p), B3PW91/6-31G(2d,2p), and MPW91PW91/6-31(2p,2d) levels of theory. The bromonitriles yield the corresponding cyano-olefin and HBr gas in a rate-determining step. The MPW91PW91/6-31G(2p,2d) results suggest a concerted mechanism, with a polar, four-membered transition state. The calculated kinetic and thermodynamic parameters were found to be within reasonable agreement with the experimental determinations. Substituent effects are discussed in terms of electronic structure.