Tri-butyltin hydride (Bu3SnH) is used synthetically to reduce alkyl halides, replacing a halogen atom with hydrogen. Free-radical initiators promote this reaction, and free-radical inhibitors are known to slow it or stop it. Your job is to develop a mechanism, using the following reaction as the example.

The following bond-dissociation enthalpies may be helpful:

(a) Propose initiation and propagation steps to account for this reaction.
(b) Calculate values of ΔH for your proposed steps to show that they are energetically feasible.

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trace Br, Inv BrBuSnH H + + BuSnBr Br B 192 kJ/mol H-Br 368 kJ/mol BujSn H 310 kJ/mol Bu3Sn Br 552 kJ/mol Br 397 kJ/mol 285 kJ/mol