See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: The Degree of Unsaturation (DoU), also called Double Bond Equivalent (DBE), is calculated using the formula: DBE = (2C + 2 + N - H - X) / 2, where C = number of carbons, H = number of hydrogens, N = number of nitrogens, X = number of halogens. Step 1: Determine the molecular formula of cubane. Cubane has 8 carbon atoms arranged at the corners of a cube, each bearing exactly one hydrogen atom. Therefore, the molecular formula is C8H8. Step 2: Apply the DBE formula. DBE = (2C + 2 - H) / 2 DBE = (2(8) + 2 - 8) / 2 DBE = (16 + 2 - 8) / 2 DBE = 10 / 2 DBE = 5 Step 3: Interpretation. Cubane has no actual double bonds or triple bonds, but its 5 degrees of unsaturation arise from the 5 rings present in the cubane framework (a cube has 6 faces, but only 5 are independent rings; equivalently, with 8 carbons in a saturated acyclic chain C8H18, cubane C8H8 has 10 fewer hydrogens, giving 10/2 = 5 DBE, all from rings). Why other options fail: - (a) 4: Undercounts the ring closures in the cubic framework. - (c) 6: Overcounts; cubane has only 5 independent rings. - (d) 7: Significantly overcounts. Therefore, the correct answer is B.