Carboxylic acids are among the most acidic organic compounds due to the stabilization of their conjugate base, the carboxylate ion, through two equivalent resonance structures. This contrasts with phenols, where the phenoxide ion has non-equivalent resonance structures, making carboxylic acids more acidic than phenols.
Why are carboxylic acids considered amongst the most acidic organic compounds, and how does their acidity compare to phenols?
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Carboxylic acids are highly acidic due to the resonance stabilization of their conjugate base, the carboxylate ion. Resonance disperses the negative charge between the oxygen atoms, stabilizing the ion. Additionally, the electronegative oxygen atoms withdraw electron density from the acidic hydrogen, enhancing its acidity. In comparison, phenols are less acidic than carboxylic acids because their phenoxide ions lack resonance stabilization. While phenols exhibit some acidity due to the electron-withdrawing effect of the aromatic ring, it is generally weaker than that of carboxylic acids. Thus, the resonance stabilization of carboxylate ions contributes to the heightened acidity of carboxylic acids.