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1. Consider the radical halogenation reaction shown below to answer parts a-c. Note that "Ph" refers to a benzene ring. BDE (kJ/mol) a. Draw the major monobrominated organic product for the reaction. Initiation Br₂, heat Propagation Step 1. Major Organic + HBr Product Step 2. Bond CH3CH₂-H (CH3)3C-H PhCH₂-H b. Draw an arrow-pushing mechanism that shows the reaction pathway leading to the formation of the major organic product. If multiple stereoisomers are formed, only draw the mechanism for one of them. Termination (Draw one termination step.) CH3CH₂-Br (H3C)3C-Br PhCH₂-Br H-Br Br-Br 423 404 378 303 304 264 368 190
c. Calculate AH° for the first propagation step for this reaction. Show your work and include units. d. Calculate AH° for the second propagation step for this reaction. Show your work and include units. e. Draw a reaction coordinate diagram for the two-step propagation cycle for the reaction. Include the two AH values that you calculated previously in the diagram. Label the rate- determining step. Label each step as exothermic or endothermic. f. Draw the transition state for the rate-determining step. Does the transition state look most like the alkane starting material, the radical intermediate, or halogenated product? Explain your answer. (Hint: Hammond Postulate.) g. Bromination is 80× more selective for the secondary position than the primary position. Using this information, complete the chart and determine what percentage of the experimental product yield will have substitution at each position. Only consider monobromination products. Primary Secondary Statistical Experimental Yield (%) Selectivity