Kinetics of the reaction of C 6 H 5 with HBr and DBr

The rate constants for the reaction of C 6 H 5 with HBr and DBr have been measured with the cavity–ring–down method in the temperature range of 297 to 523 K and 297 to 500 K, respectively. These rate constants can be effectively represented, in units of cm 3 /s, by\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} k_{{\rm HBr}} = 10^{- 10.40 \pm 0.24} \exp \left[{{{\left({- 554 \pm 208} \right)} \mathord{\left/ {\vphantom {{\left({- 554 \pm 208} \right)} T}} \right. \kern-\nulldelimiterspace} T}} \right]{\rm and} \\ k_{{\rm DBr}} = 10^{- 10.36 \pm 0.17} \exp \left[{{{\left({- 662 \pm 151} \right)} \mathord{\left/ {\vphantom {{\left({- 662 \pm 151} \right)} T}} \right. \kern-\nulldelimiterspace} T}} \right]{\rm.} \\ \end{array} $$\end{document}Both activation energies are similar and positive, contrary to those of alkyl radical reactions, all of which exhibit negative temperature dependencies. The difference, as pointed out before [1], could be accounted for by the electron‐withdrawing effect of the phenyl vis‐à‐vis the electron‐donating ability of the alkyls. © 1994 John Wiley & Sons, Inc.