See image — Practical Organic Chemistry and Purification Chemistry Question

💡 Solution & Explanation

Step 1 - Analyze the polymer structure: The polymer shown is a carbon-chain backbone where every other carbon (the repeat unit carbon) is quaternary, bearing two CO2Me (methoxycarbonyl) groups - one on a wedge bond and one on a normal bond. The repeat unit is -[CH2-C(CO2Me)2]n-, meaning each monomer unit contributes a -CH2-C(CO2Me)2- segment. Step 2 - Identify the monomer via addition polymerization: In addition (chain-growth) polymerization of a vinyl monomer CH2=CX2, the double bond opens and each monomer adds to give repeat units -CH2-CX2-. For the polymer shown with two CO2Me groups on the same carbon, the monomer must be CH2=C(CO2Me)2, i.e., vinylidene dimethyl malonate (dimethyl methylenemalonate). Step 3 - Match to option (c): Option (c) depicts a vinylidene structure (CH2= with two substituents on the same carbon). The structure in option (c) shows CH2=C with both a branch and CO2Me, which corresponds to CH2=C(CO2Me)2 when both substituents on the sp2 carbon are CO2Me groups. This is consistent with the polymer's repeat unit having a quaternary carbon bearing two CO2Me groups. Step 4 - Eliminate other options: - Option (a): CH2=CH-CH2CO2Me would give a polymer with CO2Me pendant one carbon away from the backbone, not a gem-di(CO2Me) quaternary center. - Option (b): Has a methyl group plus CO2Me on the vinylidene carbon (methyl methacrylate-type), giving only one CO2Me per repeat unit quaternary carbon, not two. - Option (d): An internal alkene (CH3CH=CHCO2Me, methyl crotonate) would give a different backbone connectivity and only one CO2Me group per unit. Therefore, the correct answer is C.