See image — Hydrocarbons Chemistry Question

💡 Solution & Explanation

Concept: The Kolbe electrolysis reaction involves the electrolytic decarboxylation of carboxylate salts at the anode. Each carboxylate anion loses CO2 and one electron to form a carbon radical, and two such radicals couple to form the product. Step 1: Identify the starting material. The compound is the dipotassium salt of 2,3-dimethylsuccinic acid (or more precisely, it is the potassium salt of a compound where two CH(CH3)CO2K groups are joined — this is the dipotassium salt of 2,3-dimethylsuccinic acid). Wait — re-reading the structure: CH3-CH-CO2K | CH3-CH-CO2K. The vertical line indicates a C-C bond between the two CH groups. So the compound is the dipotassium salt of 2,3-dimethylsuccinic acid: KO2C-CH(CH3)-CH(CH3)-CO2K. Step 2: Kolbe electrolysis mechanism. At the anode, both carboxylate groups undergo oxidative decarboxylation simultaneously: KO2C-CH(CH3)-CH(CH3)-CO2K → -2CO2, -2e- → •CH(CH3)-CH(CH3)• (diradical intermediate) OR the two carboxylates lose CO2 to give two •CH(CH3) radicals that couple, but since they are in the same molecule (intramolecular), a diradical forms and cyclizes. Step 3: Since both -CO2K groups are on adjacent carbons, after losing 2 CO2, the two radical centers are on adjacent carbons, forming a 1,2-diradical: •CH(CH3)-CH(CH3)•. This intramolecular diradical undergoes ring closure to form a three-membered ring — but that would give dimethylcyclopropane. Step 4: Re-examining — the intramolecular Kolbe on a succinate gives cyclopropane derivatives. Specifically, 2,3-dimethylsuccinate gives 1,2-dimethylcyclopropane... but the options show but-2-ene (option c) as the answer. Step 5: Actually, for intramolecular Kolbe electrolysis of the dipotassium salt of 2,3-dimethylsuccinic acid, the two radical centers on C2 and C3 (after loss of both CO2) are adjacent, and they can either couple to form dimethylcyclopropane or undergo disproportionation/elimination to form but-2-ene (CH3-CH=CH-CH3). The disproportionation pathway (one radical donates H to the other) gives the alkene as the major product. Since the two CH(CH3) radicals are adjacent, loss of H from one and addition to the other gives cis/trans-but-2-ene. The cis isomer (option c) is the major product due to the geometry of the transition state. Step 6: Why other options fail: - (a) but-1-ene: would require terminal double bond, not consistent with central radical coupling/disproportionation - (b) cyclobutane: would require two separate intermolecular radical couplings giving a 4-carbon ring, not from this substrate - (d) cyclobutene: not consistent with the radical mechanism here The major product of intramolecular Kolbe electrolysis of dipotassium 2,3-dimethylsuccinate is cis-but-2-ene (option c) via disproportionation of the intermediate diradical. Therefore, the correct answer is C.