Chemistry - GOC Question with Solution | TestHub

Addition across ${\mathrm{C}}_9-{\mathrm{C}}_{10}$ leaves two intact benzene rings (2 × 36 = 72 kcal/mol), so the loss is 84 - 72 = 12 kcal/mol. Addition across a bond in a terminal ring would leave a naphthalene-type system only if one ring is lost, which costs more. So ${\mathrm{C}}_9-{\mathrm{C}}_{10}$ reacts.