Why Is the Carbonyl Oxygen Atom of Carboxylic Acids and Derivatives Protonated in the Acid-Catalyzed Reactions
XU Jia-Xi1**, MA Yuan2
1. College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, China; 2. Department of Chemistry, Tsinghua University, Beijing 100084, China
Abstract The oxygen atom in alcohols and ethers is more basic than that of the carbonyl group in aldehydes and ketones. However, the carbonyl oxygen atom of carboxylic acid and derivatives is protonated in their acid-catalyzed reactions. In addition, when carboxylic acids and derivatives are used as nucleophiles, their carbonyl oxygen atom serves as the nucleophilic site. This article rationally explains the reason why the carbonyl oxygen atom of carboxylic acids and derivatives is readily protonated in their acid-catalyzed reactions and serves as the nucleophilic site when they are used as nucleophiles through analyzing the electronic effect in their π43 conjugative systems between the carbonyl group with the oxygen/nitrogen atom. The rationale can be extended to the protonation of imidates, amidines, and guanidines. It would provide a deeper understanding on the influence of the electron density of different atoms in isolated systems and conjugative systems for students.
XU Jia-Xi, MA Yuan. Why Is the Carbonyl Oxygen Atom of Carboxylic Acids and Derivatives Protonated in the Acid-Catalyzed Reactions[J]. Chinese Journal of Chemical Education, 2024, 45(2): 127-129.
