See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: Addition of D-Cl (deuterium chloride) to an alkene follows Markovnikov's rule and proceeds via an electrophilic addition mechanism. Step 1: Identify the substrate. The starting material is 1-methylenecyclobutane — a cyclobutane ring with an exocyclic double bond (=CH2 bearing the CH3, i.e., actually methylenecyclobutane where the exocyclic carbon bears a CH3 group, making it 1-(1-methylethylidene) or more precisely the structure shown is cyclobutylidene with a CH3 on the exocyclic carbon). The double bond is between the ring carbon (C1 of cyclobutane) and the exocyclic carbon that also bears a CH3. Step 2: Apply Markovnikov's rule for D-Cl addition. The electrophile D+ (deuterium proton) adds to the less substituted carbon of the double bond. The exocyclic carbon bearing CH3 is more substituted (secondary/tertiary character due to CH3), while the ring carbon C1 of cyclobutane is tertiary (connected to two ring carbons). Wait — the exocyclic =C(CH3) carbon is less substituted (it has CH3 and =), and the ring carbon is more substituted (attached to two CH2 groups of the ring). By Markovnikov's rule, D+ adds to the exocyclic carbon (less substituted end), generating a tertiary carbocation at the ring carbon C1 of cyclobutane. Actually re-examining: exocyclic carbon has CH3 (one substituent besides H count: it's =C(H)(CH3) so it's like a vinylic CH with CH3, making it the less substituted end). D+ adds to exocyclic =CH-CH3 carbon → carbocation forms at C1 of the ring (tertiary, stabilized by the two ring carbons). Step 3: Cl- then attacks the carbocation at C1 of the ring. Step 4: Stereochemistry. The addition of HCl (or DCl) to alkenes is typically anti addition in ionic mechanism (Cl- attacks from opposite face to D+), but for simple electrophilic addition through an open carbocation, both faces are possible, though the major product tends to show anti addition geometry. In option (b), D is on the wedge (one face) at the exocyclic carbon position, and Cl is on the ring carbon on the opposite relative configuration, consistent with anti addition. The CH3 remains on the exocyclic carbon now bonded to the ring, and Cl is on C1 of the ring. Step 5: Evaluating options. Option (b) shows the cyclobutane ring with CH3 and Cl on C1 of the ring (Cl on the lower right, consistent with ring carbon), D added to the exocyclic position now part of the ring framework on the wedge (left), and H at bottom — this is consistent with Markovnikov addition of D to the terminal exocyclic carbon and Cl to the internal ring carbon, with anti stereochemistry placing D and Cl on opposite faces. Why other options fail: - Option (a): Has H instead of D at the position where deuterium should add; does not reflect DCl addition. - Option (c): Shows D on top and Cl at bottom-left with CH3 at bottom-right — the regiochemistry places substituents inconsistently with Markovnikov's rule. - Option (d): Shows Cl on the wedge at the ring carbon and D on top, which would correspond to a syn addition or incorrect regiochemistry. Therefore, the correct answer is B.