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16.10 The calculated resonance energy for phenanthrene is 92 kcal/mol (385 kJ/mol). The product has two benzene rings so its approximate resonance energy is 2(36) = 72 kcal/mol (301 kJ/mol). Therefore the resonance energy lost is equal to (92 - 72) = 20 kcal/mol (83.6 kJ/mol). Addition to one of the other double bonds leaves a Br naphthalene derivative, with an approximate Br resonance energy of 61 kcal/mol (255 kJ/mol), so the resonance energy lost is approximately 31 kcal/mol (129.6 kJ/mol). 16.11 This compound has 18 TT electrons, so it is 9.5 δ aromatic. The diamagnetic ring current induces a magnetic field that is parallel to H the external magnetic field on the outside of the ring and opposed in the center of H the ring. This causes the NMR signals of hydrogens on the outside of the ring to appear downfield and the hydrogens inside the ring to appear upfield from the position of normal alkene hydrogens. 16.12 a) The compound on the left is a stronger acid because its conjugate base is aromatic. b) The compound on the right is a stronger acid because conjugate base of the other compound is antiaromatic. c) The compound on the right is a stronger acid because its conjugate base is aromatic. 16.13 The compound on the left has the faster rate of substitution by the SN1 mechanism because the carbocation that is formed from it is aromatic. 240