first chain propagation step of all radical halogenation reactions we considered

Chapter 8, Problem 8.21

(choose chapter or problem)

first chain propagation step of all radical halogenation reactions we considered inSection 8.5B was abstraction of hydrogen by the halogen atom to give an alkyl radical andHX, as for exampleCH3CH3 1 ? Br CH3CH2 ? 1 HBrSuppose, instead, that radical halogenation occurs by an alternative pair of chain propa-gation steps, beginning with this step.CH3CH3 1 ? Br CH3CH2Br 1 H?(a) Propose a second chain propagation step. Remember that a characteristic of chainpropagation steps is that they add to the observed reaction.(b) Calculate the heat of reaction, DH 0, for each propagation step.(c) Compare the energetics and relative rates of the set of chain propagation steps inSection 8.5B with the set proposed here.