See image — GOC and Organic Chemistry Basics Chemistry Question

💡 Solution & Explanation

CONCEPT: The acidity of carboxylic acids is governed by inductive/field effects of electronegative substituents (like Br). More electronegative substituents closer to the COOH group stabilize the carboxylate anion more, increasing acidity. Multiple substituents increase acidity more than one. Distance reduces the inductive effect. PART (a): All four compounds are bromocyclohexanecarboxylic acids (or a bicyclic variant). The key factors are: (1) number of bonds between Br and COOH (closer = more acidic), and (2) geometry/conformation affecting through-space field effect. - (iv) 1-bromobicyclo[2.2.1]heptane-2-carboxylic acid (norbornane system): Br is at the bridgehead (C1) and COOH is at C2, so Br is on the alpha carbon relative to COOH — very close, AND the rigid bicyclic structure holds Br in a fixed geometry with a strong through-space field effect toward the carboxylate. This makes it the MOST acidic. - (ii) 1-bromocyclohexane-1-carboxylic acid: Br is on the same carbon as COOH (alpha position), giving a strong inductive effect. This is the second most acidic. - (i) 3-bromocyclohexane-1-carboxylic acid: Br is at C3, two carbons away from COOH (beta position). The inductive effect is attenuated. Third most acidic. - (iii) 4-bromocyclohexane-1-carboxylic acid: Br is at C4, three carbons away from COOH. The inductive effect is most attenuated. Least acidic. Ranking (a): iv > ii > i > iii PART (b): All compounds are alpha-substituted acetic/propanoic/butanoic acids. Key factor: number of Br atoms on or near the alpha carbon. - (iii) Has THREE Br atoms (two on alpha carbon, one on beta carbon): strongest combined inductive effect. MOST acidic. - (iv) Has TWO Br atoms on alpha carbon plus one Br on beta carbon — wait, examining structure: alpha carbon has two Br, and the chain has one more Br (on beta). Actually comparing (iii) and (iv): both appear to have three Br total but differ in placement. (iii) has Br, Br on alpha and Br on the next carbon (closer arrangement or same number). (iv) has Br, Br on alpha and one Br further along chain. Since (iii) has all Br atoms in closest proximity to COOH, it is more acidic than (iv). Second most acidic: iv. - (i) Has ONE Br on alpha carbon plus alkyl groups (methyl and ethyl): moderate inductive effect. Third most acidic. - (ii) Pivalic acid — NO Br, only methyl groups which are electron-donating (slightly destabilize carboxylate). LEAST acidic. Ranking (b): iii > iv > i > ii Therefore, the correct answer is {"a": ["iv", "ii", "i", "iii"], "b": ["iii", "iv", "i", "ii"]}.