Tributyltin hydride (Bu₃SnH) can be used to synthetically reduce alkyl halides. In this process, a halogen atom is replaced by a hydrogen atom. Suggest a mechanism for the initiation and propagation steps for the reaction below. 
Using the following bond-dissociation enthalpies, calculate the values of ΔH for the proposed steps and determine whether each step is energetically favorable.

• A. Initiation step: ΔH = +190 kJ/molPropagation step:(1) ΔH = –119 kJ/mol(2) ΔH = –103 kJ/molThe overall enthalpy of the reaction is highly exothermic, making this mechanism energetically favorable.
• B. Initiation step: ΔH = +190 kJ/molPropagation step:(1) ΔH = +119 kJ/mol(2) ΔH = +103 kJ/molThe overall enthalpy of the reaction is highly endothermic, making this mechanism energetically favorable.
• C. Initiation step:(1) ΔH = +190 kJ/mol(2) ΔH = –56 kJ/molPropagation step:(1) ΔH = –243 kJ/mol(2) ΔH –103 kJ/molThe overall enthalpy of the reaction is highly exothermic, making this mechanism energetically favorable.
• D. Initiation step:(1) ΔH = –190 kJ/mol(2) ΔH = +56 kJ/molPropagation step:(1) ΔH = +243 kJ/mol(2) ΔH +103 kJ/molThe overall enthalpy of the reaction is highly endothermic, making this mechanism energetically favorable.

Answer: (C)