Name: proton transfer in brønsted-lowry reactions
Uploaded: 2025-05-22T09:05:33.000Z
Duration: 2 min 16 s
Channel: JoVE

From the sour taste of vinegar in salad dressings to the caustic liquids used as drain cleaners, acids and bases have many applications.
According to the Br&#248;nsted-Lowry theory, an acid is a proton donor, and a base is a proton acceptor; thus, an acid&#8211;base reaction is a proton-transfer reaction. 
Examine the reaction between the Br&#248;nsted acid &#8212; acetic acid &#8212; and the Br&#248;nsted base &#8212; ammonia. The nitrogen atom in ammonia, owing to its lone pair, serves as the proton receptor site.
Proton transfer from the acid to the base is shown using curved arrows, which illustrate the movement of electrons.
The arrow from the base denotes the shift of nonbonding electrons to the proton of the acid, forming a new covalent bond.
The arrow on the acid shows that the O&#8211;H bond breaks to release a proton and that its electrons shift entirely to the oxygen atom.
The acetate ion that remains from the deprotonation of acetic acid is the conjugate base. The ammonium ion, resulting from the protonation of ammonia, is the conjugate acid. 
Notice that acetic acid has two potential proton receptor sites &#8212; the carbonyl oxygen and the hydroxyl oxygen &#8212; and that it functions as a Br&#248;nsted base in its reaction with s

br&#248;nsted-lowry acids and bases

Br&#248;nsted-Lowry Acids and Bases

In 1923, the Br&#248;nsted&#8211;Lowry definition of acids and bases was proposed by Johannes Br&#248;nsted and Thomas Lowry. According to this theory, a Br&#248;nsted acid is defined as a species that donates a proton in a chemical reaction and gets converted to its conjugate base. A Br&#248;nsted base is defined as a species that accepts a proton in a chemical reaction and gets converted into its conjugate acid. These transfers of protons are caused by the displacement of electrons in these reactions, which is represented by curved arrows. 
Consider the following reaction between acetic acid and ammonia as shown in figure 1. 
<img alt="Acid-base reaction mechanism diagram; CH&#8323;COOH + NH&#8323; &#8652; CH&#8323;COO&#8315; + NH&#8324;&#8314;." src="/files/ftp_upload/11733/11733_PT_Figure%201.svg" style="text-align: center; height: 90px;" data-altupdatedat="1754904545000" data-alt="Acid-base reaction mechanism; CH3COOH + NH3 equilibrium; chemical structures diagram." />
 Figure 1. Reaction between acetic acid and ammonia
In this reaction, the transfer of two-electron pairs is shown by curved arrows, symbolizing the proton transfer from the acetic acid to ammonia in this acid&#8212;base reaction. The two curved arrows in this reaction depict the two electron-pair shifts. One electron pair is transferred from ammonia to the acetic acid, and another is transferred from the O&#8212;H bond of the acetic acid to the oxygen. This, in turn, results in the transfer of a proton from an acetic acid molecule to an ammonia molecule. Thus, the acetate ion and ammonium ion are formed as the conjugate base and conjugate acid in this reaction.

In 1923, the Br&#248;nsted&#8211;Lowry definition of acids and bases was proposed by Johannes Br&#248;nsted and Thomas Lowry. According to this theory, a ...

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Acids and Bases

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proton transfer in brønsted-lowry reactions

Brønsted-Lowry acids and bases are defined by proton transfer in a chemical reaction. In this model, a Brønsted acid donates a proton and becomes its conjugate base. A Brønsted base accepts a proton and becomes its conjugate acid.

This theory was proposed in 1923 by Johannes Brønsted and Thomas Lowry. It helps explain acid-base reactions by tracking how protons move between species. The electron shifts that drive these transfers are shown with curved arrows.

A reaction between acetic acid and ammonia shows this process clearly. One curved arrow shows an electron pair moving from ammonia to the acetic acid. Another curved arrow shows an electron pair moving from the O-H bond of acetic acid to the oxygen. These electron-pair shifts lead to proton transfer from acetic acid to ammonia.

As a result, acetate ion and ammonium ion are formed. The acetate ion is the conjugate base of acetic acid. The ammonium ion is the conjugate acid of ammonia.

Proton Transfer in Brønsted-Lowry Reactions

proton-transfer-in-bronsted-lowry-reactions

Brønsted-Lowry acids and bases are defined by proton transfer in a chemical reaction. In this model, a Brønsted acid donates a proton and becomes its conjugate base. A Brønsted base accepts a proton and becomes its conjugate acid. This theory was proposed in 1923 by Johannes Brønsted and Thomas Lowry. It helps explain acid-base reactions by tracking how protons move between species. The electron shifts that drive these transfers are shown with curved arrows. A reaction between acetic acid and...

lewis acids and bases

Electron-Pair Reactions in Lewis Theory

Lewis theory explains acid-base reactions through electron pairs, especially for electron-deficient compounds that do not fit the Brønsted definition. It is often used to describe group 13 elements such as boron and aluminium. These elements have three valence electrons, so their trivalent compounds can have a sextet of electrons and an empty orbital at the central atom. Because of that electron shortage, these compounds can accept electrons from another species to complete their octet.

acid and bases: ka, pka, and relative strengths

acid-and-bases-ka-pka-and-relative-strengths

Comparing Acid and Base Strength with pKa

Acid and base strength can be compared using Ka and pKa. These values help show how much an acid dissociates in water and how strong a base is through its conjugate acid. Acid strength depends on dissociation into a conjugate base and hydronium ion in water. A strong acid dissociates almost completely, so the hydronium ion concentration is very high. A weak acid dissociates only partly, so more acid remains undissociated and the equilibrium stays farther back. For dilute weak acids, the...

position of equilibrium in acid-base reactions

position-of-equilibrium-in-acid-base-reactions

Predicting Acid-Base Equilibrium Direction

Acid-base equilibrium direction depends on acid strength and pKa values. A lower pKa means a stronger acid, while a higher pKa means a weaker acid. A negative pKa shows a stronger acid, and a positive pKa shows a weaker acid. In the reaction between ammonia and an ethoxide ion, ethanol has a pKa of 15.9 and ammonia has a pKa of 38. That means ethanol is the stronger acid in this pair. A strong acid forms a weak conjugate base, and a weak acid forms a strong conjugate base, so the ethoxide ion...

molecular structure and acidity

What Makes One Acid Stronger?

Acid strength depends on how stable the conjugate base is after the acid loses a proton. When deprotonation forms a more stable anion, the acid is stronger. If the anion is unstable, the acid is weaker. Chemists compare several structure-based factors to judge that stability. One factor is size. When acids come from elements in the same column of the periodic table, atomic size is compared. A larger atom can spread out a negative charge over a bigger space. That makes the conjugate base more...

leveling effect and non-aqueous acid-base solutions

leveling-effect-and-non-aqueous-acid-base-solutions

Solvent Effects on Strong Acids and Bases

Solvent effects can change how strong acids and bases react in a chemical system. The leveling effect is one important example. It shows that a solvent can take part in the reaction before the acid and base react with each other. For a generic acid-base reaction, a generic acid (HA) reacts with a generic base (B−) to form the conjugate base (A−) and the conjugate acid (HB). In a solvent called HX, the solvent may also react if it is stronger than one of the reactants. If HA is weaker than the...

solvating effects

How Solvation Changes Acidity

Solvation changes acidity by affecting how stable a conjugate base is. The strength of an acid is commonly compared with its pKa value. When an ion dissolves, solvent molecules surround it and help stabilize it through solvation. Solvation of ions can happen in three main ways. In donor interaction, the solvent donates unshared electron pairs to the ion. The solvent acts as a Lewis base, and the ion acts as a Lewis acid. In charge-dipole interaction, polar solvent molecules align their partial...

key terms and concepts

Explore how Brønsted-Lowry acids and bases transfer protons, use curved arrows, and form conjugate acid-base pairs in a reaction with acetic acid and ammonia.

Proton Transfer in Brønsted-Lowry Reactions | JoVE K12

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Proton Transfer in Brønsted-Lowry Reactions

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