Maximally inhibited elimination of kinetics of (2‐bromoethyl)benzene and 1‐bromo‐3‐phenylpropane in the gas phase. Anchimeric assistance of the phenyl group

The gas‐phase elimination kinetics of (2‐bromoethyl)benzene and 1‐bromo‐3‐phenylpropane were studied in a static system and seasoned vessels over the temperature range 390–450 °C and the pressure range 32–104 Torr. The reactions, under maximum inhibition of 4‐fold pressure of the free‐radical suppressor cyclohexene and/or propene, are homogeneous, unimolecular and obey a first‐order rate law. The rate coefficients are given by the following Arrhenius equations: for (2‐bromoethyl)benzene, log k 1 (s −1 ) = (13·04 ± 0·10) − (210·8 ± 1·3) kJ mol −1 (2·303 RT ) −1 , and for 1‐bromo‐3‐phenylpropane, log k 1 (s −1 ) = (14·09 ± 0·27) − (227·7 ± 3·6) kJ mol −1 (2·303 RT ) −1 . The phenyl group of (2‐bromoethyl)benzene appears to provide anchimeric assistance in the HBr elimination of this compound. However, neighbouring C 6 H 5 participation at the 3‐position in 1‐bromo‐3‐phenylpropane for a C‐4 conformation is apparently absent. The mechanisms of these reactions are discussed.