See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: The reaction of an alkene with diazene (or its deuterated analog ND2-ND2) in the presence of H2O2 is a syn addition of two hydrogen (or deuterium) atoms across the double bond. Deuterated diazene (ND2-ND2) decomposes to deliver two D atoms in a concerted, syn (cis) fashion to the same face of the double bond. Step 1: Identify the reagent. ND2-ND2 is deuterated diazene (dideuteriodiazene). In the presence of H2O2 (an oxidant that can generate diazene in situ or facilitate its reaction), diazene undergoes a concerted syn addition across the double bond. Step 2: Reaction mechanism. Diazene adds both D atoms simultaneously from the same face of the alkene (syn addition), releasing N2 as a byproduct. This is analogous to catalytic hydrogenation (which is also syn) but here both atoms added are deuterium. Step 3: Apply to cyclohexene. Cyclohexene has a double bond between C1 and C2. Syn addition of D2 (from ND2-ND2) delivers both D atoms to the same face of the ring. This gives 1,2-dideuterocyclohexane where both D atoms are on the same face (cis relationship), i.e., the cis (syn) product. Step 4: Stereochemical outcome. The syn addition gives the cis-1,2-dideuterocyclohexane. In the drawing, this corresponds to option (b), where both D atoms are shown on wedge bonds on the same face of the cyclohexane ring (syn/cis addition product). Step 5: Why other options fail. - Option (a): Plain cyclohexane with no deuterium is wrong because deuterium atoms are incorporated from ND2-ND2. - Option (c): Shows trans (anti) addition product with D atoms on opposite faces, which would result from anti addition. Diazene addition is strictly syn, not anti, so this is incorrect. - Option (d): Both (b) and (c) would imply both syn and anti products, but diazene addition is stereospecifically syn only. Therefore, the correct answer is B.