An electron diffraction investigation of the reaction intermediate in the gashyphen;phase bromination of ethylene

摘要

The addition of bromine to ethylene was studied in the gas phase by electron diffraction. Atomic bromine and an excess of ethylene were mixed just prior to introduction into the scattering region by a dualhyphen;sample inlet system. The atomic bromine was produced from molecular bromine by thermolysis in an oven adjacent to the mixing region. Diffraction patterns recorded at each of three different oven temperatures were analyzed. The radial distribution curve for one pattern had the normal distances attributed to ethylene and bromine plus a Brsngbnd;Br peak corresponding to the3Pgr;0plus;mgr;state ofBr2.The radial distribution curve for a second pattern exhibited a peak at 1.7 Aring; in addition to the ethylene and bromine distances. The radial distribution curve for a third pattern, recorded at the highest oven temperature, again showed the 1.7 Aring; peak and ethylene peaks but no bromine peak. To account for the scattering power and still preserve stoichiometry, it was necessary to assign the 1.7 Aring; peak to a carbonhyphen;bromine pair with a double weight. This implies that the intermediate in the bromination of ethylene has a bromine atom symmetrically bonded to each of the two carbon atoms.