Consider the three fundamental positional isomers of nitrophenol: o-nitrophenol, m-nitrophenol, and — GOC and Organic Chemistry Basics Chemistry Question
Question
Consider the three fundamental positional isomers of nitrophenol: o-nitrophenol, m-nitrophenol, and p-nitrophenol. Exactly how many of these specific isomers display an experimentally measured acidic strength distinctly GREATER than that of unsubstituted phenol (meaning they possess a proportionally lower $pKa$ value)?
💡 Solution & Explanation
The nitro group ($-NO_2$) is a powerful electron-withdrawing functional group. At the ortho and para positions, it stabilizes the phenoxide conjugate base through intense $-M$ and $-I$ effects. At the meta position, it stabilizes the base solely through a strong $-I$ effect. Because all three positional isomers benefit from some degree of electron-withdrawing stabilization compared to unsubstituted phenol, all 3 isomers are significantly more acidic than phenol.