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Polyprotic Acids

Polyprotic Acids

Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ionizable hydrogen atom in each molecule are called monoprotic acids. Their reactions with water are:

Acid Halides to Carboxylic Acids: Hydrolysis

Acid Halides to Carboxylic Acids: Hydrolysis

Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...

Physical Properties of Carboxylic Acids

Physical Properties of Carboxylic Acids

Carboxylic acids with lower molecular weight exhibit a sharp and unpleasant odor. They also have higher boiling and melting points than analogous compounds, such as aldehydes, ketones, and alcohols.

Reactions of Carboxylic Acids: Introduction

Reactions of Carboxylic Acids: Introduction

Carboxylic acids possess an acidic –COOH functional group. The acidity can be attributed to the resonance stabilization of their conjugate base, wherein the negative charge is delocalized over both oxygen atoms.

Composition of Polyprotic Acid Solutions as a Function of pH

Composition of Polyprotic Acid Solutions as a Function of pH

Polyprotic acids of the type H2M constitute two ionizable protons. As a result, on titration with a base, they exhibit two equivalence points in the titration curve. During titration, the species H2M, HM−, and M2− will be present in the solution at different points. The fractions of H2M, HM−, and M2− present at the various instances of the titration are denoted by α0, α1, and α2, respectively.
A graph with the alpha values is plotted against the volume of base added during titration. Here, a...

Acidity of Carboxylic Acids

Acidity of Carboxylic Acids

Carboxylic acids are the strongest organic acids. However, their acidic strength is much less than mineral acids like HCl. Carboxylic acids ionize in water and readily lose the hydroxyl proton to form a resonance-stabilized carboxylate ion.

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Related Experiment Video

Updated: Jun 27, 2026

Facile Protocol for the Synthesis of Self-assembling Polyamine-based Peptide Amphiphiles (PPAs) and Related Biomaterials

Facile Protocol for the Synthesis of Self-assembling Polyamine-based Peptide Amphiphiles (PPAs) and Related Biomaterials

Published on: June 25, 2018

Proton Sharing in Polycarboxylic Acids in Aqueous Solution.

Lukáš Tomaník^1,2, Jiří Tůma³, Gunnar Öhrwall⁴

¹Department of Physical Chemistry, University of Chemistry and Technology, Prague, Technická 5, Prague 16628, Czech Republic.

|June 26, 2026

Summary

Proton sharing in polycarboxylic acids is rare in water, except for maleic acid. This finding emphasizes the role of enzymes in metabolic processes involving proton sharing.

Keywords:

Biomolecules Carboxylic Acids Citric Acid (Krebs) Cycle Photoelectron Spectroscopy Proton Sharing

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Determination of the Gas-phase Acidities of Oligopeptides

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Published on: June 24, 2013

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Last Updated: Jun 27, 2026

Facile Protocol for the Synthesis of Self-assembling Polyamine-based Peptide Amphiphiles (PPAs) and Related Biomaterials

Facile Protocol for the Synthesis of Self-assembling Polyamine-based Peptide Amphiphiles (PPAs) and Related Biomaterials

Published on: June 25, 2018

Determination of the Gas-phase Acidities of Oligopeptides

Determination of the Gas-phase Acidities of Oligopeptides

Published on: June 24, 2013

Area of Science:

Biochemistry
Physical Chemistry
Spectroscopy

Background:

Proton sharing in polycarboxylic acids is crucial for biological processes.
Understanding proton distribution in aqueous solutions is challenging.
Existing techniques like NMR provide time-averaged data.

Purpose of the Study:

To investigate intramolecular proton sharing in biologically relevant polycarboxylic acids.
To determine the prevalence of proton sharing in aqueous environments.
To utilize the ultrafast probing capabilities of X-ray photoelectron spectroscopy.

Main Methods:

Liquid-jet X-ray photoelectron spectroscopy (XPS) was employed.
XPS captures instantaneous proton distribution due to its ultrafast time scale.
Analysis of carbon 1s spectra to identify proton localization or delocalization.

Main Results:

Significant proton sharing was only observed in maleic acid's monoanionic form.
Maleic acid exhibited a single, delocalized peak in its carbon 1s spectrum.
Succinic, fumaric, malic, glutaric, and citric acids showed distinct peaks indicating localized proton groups (COOH and COO⁻).

Conclusions:

Intramolecular proton sharing is an exception for most biologically relevant polycarboxylic acids in water.
Enzyme-driven structural changes are critical for proton sharing in metabolic pathways.
XPS is a powerful tool for studying ultrafast proton dynamics.