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VII. [40 Points] We have learned that the bromination of ethene proceeds via a bromonium ion to give 1,2-dibromoethane. With light or a radical initiator, an alternative mechanism can be formulated, traversing a radical chain pathway: ho + Br2 AH° = ? kcal mol-1 Br Br Answer the following questions in the order a.–f. on your first appended page, labelled "VII.". a. Using the bond dissociation energies in the Table below, the energy of the it bond, 65 kcal mol-1, and the strength of the Br-Br bond, 46 kcal mol-1, calculate the AH° of this reaction. Show your work. Label this part "a.”. Table 3.1 Bond-Dissociation Energies of Various A-B Bonds in the Gas Phase (DH° in kcal mol-' (kJ mol-')] B in A-B A in A-B -H -F -CI -Br -I -OH -NH2 H- 104 (435) 136 (569) 103 (431) 87 (364) 71 (297) 119 (498) 108 (452) CH- 105 (439) 110 (460) 85 (356) 70 (293) 57 (238) 93 (389) 84 (352) CH3CH2- 101 (423) 111 (464) 84 (352) 70 (293) 56 (234) 94 (393) 85 (356) CH,CH2CH2- 101 (423) 110 (460) 85 (356) 70 (293) 56 (234) 92 (385) 84 (352) 98.5 (412) (CH3)2CH- 111 (464) 84 (352) 71 (297) 56 (234) 96 (402) 86 (360) (CH3)3C- 96.5 (404) 110 (460) 85 (356) 71 (297) 55 (230) 96 (402) 85 (356) Note: (a) DH° = AH° for the process A-B → A. +.B. (b) These numbers are being revised continually because of improved methods for their measurement. (c) The trends observed for A-H bonds are significantly altered for polar A-B bonds because of dipolar contributions to DHⓇ. Write the radical chain mechanism for this reaction, the initiation and the two propagation steps, using electron-pushing fishhook arrows, and calculate the associated AH values. Label these parts “b.", "c.”, etc. b. Initiation and its AH° value c. Propagation step 1 d. Propagation step 2 e. AH° of propagation step 1 f. AH° of propagation step 2