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Solutions to Problems 53 the back carbon, C3) with respect to the other, giving all possible staggered conformations arising from rotation about the C2-C3 bond for this product molecule. The potential energy graph may be drawn immediately below the structures. CH₃ CH₃ CH₃ CH₃CH₂ H H CH₂CH₃ H H Br H Br H Br H H H CH₂CH₃ Energy 0 60 120 180 240 300 Degrees of rotation 31. First write out the propagation steps and determine the associated with each. As indicated in Problem 30, the major product derives from halogenation at C2. Sketch the graphs, using Figure 3-7 on page 107 of the text as your basic model. The transition states are located at the maxima for each of the steps on the graphs. Bromination steps: Propagation step 1 CH₃CH₂CH₂CH₂CH₃ + CH₃CHCH₂CH₂CH₃ + HBr DH° = 98.5 kcal mol⁻¹ for sec C-H bond DH° (HBr) = 87 kcal +11.5 Propagation step 2 CH₃CHCH₂CH₂CH₃ + Br₂ + Br. DH° (Br₂) = 46 kcal mol⁻¹ DH° = 71 kcal for sec C-Br bond -25 Overall = 13.5 kcal Iodination steps: Propagation step 1 CH₃CH₂CH₂CH₂CH₃ + CH₃CHCH₂CH₂CH₃ + HI DH° = 98.5 kcal mol⁻ for sec C-H bond DH° (HI) = 71 kcal mol⁻¹ +27.5 Propagation step 2 + I₂ CH₃CHICH₂CH₂CH₃ + DH° = 36 kcal mol⁻¹ DH° = 56 kcal mol⁻¹ for sec bond -20 Overall = +7.5 kcal mol⁻¹