See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

Step 1 - Key Concept: The stability of dienes depends primarily on two factors: (1) conjugation of the double bonds (conjugated dienes are more stable than isolated or cross-conjugated dienes), and (2) the degree of substitution of the double bonds (more substituted double bonds are more stable due to hyperconjugation). Step 2 - Analyze each structure: (a) The diene in option (a) has double bonds that appear to be in a homoconjugated or non-conjugated arrangement within the six-membered ring, with methyl groups at positions that do not maximize substitution on both double bonds. (b) Option (b) shows a cyclohexadiene with methyl groups, but the double bonds are not fully conjugated, and the substitution pattern is less favorable than option (c). (c) Option (c) shows a cyclohexa-2,4-diene system (conjugated diene within the ring) with methyl substituents positioned such that both double bonds are maximally substituted. The conjugated diene system (s-cis locked conformation within the ring) combined with two alkyl substituents (methyl groups) on the double bonds provides maximum stabilization through both conjugation and hyperconjugation. The methyl groups are placed on the double bond carbons, increasing substitution. (d) Option (d) has a conjugated diene but the methyl groups are positioned such that they are less effectively stabilizing the double bonds compared to option (c). Step 3 - Why (c) is most stable: In option (c), the diene is conjugated (1,3-diene system), the ring locks it in an s-cis conformation favorable for conjugation, and the methyl substituents are directly on the sp2 carbons of the double bonds, providing maximum hyperconjugative stabilization. This combination of conjugation plus disubstitution on the double bond carbons makes it the most stable diene among the four options. Step 4 - Why others fail: Options (a) and (b) have less effective conjugation or substitution patterns. Option (d) may have conjugation but lacks the optimal methyl substitution pattern on the double bond carbons that option (c) possesses. Therefore, the correct answer is C.