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Brønsted-Lowry Acids and Bases

Brønsted-Lowry Acids and Bases

In 1923, the Brønsted–Lowry definition of acids and bases was proposed by Johannes Brønsted and Thomas Lowry. According to this theory, a Brønsted acid is defined as a species that donates a proton in a chemical reaction and gets converted to its conjugate base. A Brønsted 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...

Bronsted-Lowry Acids and Bases

Bronsted-Lowry Acids and Bases

The acid-base reaction class has been studied for quite some time. In 1680, Robert Boyle reported traits of acid solutions that included their ability to dissolve many substances, to change the colors of certain natural dyes, and to lose these traits after coming in contact with alkali (base) solutions. In the eighteenth century, it was recognized that acids have a sour taste, react with limestone to liberate a gaseous substance (now known to be CO2), and interact with alkalis to form neutral...

Leveling Effect

Leveling Effect

In acid-base chemistry, the leveling effect refers to the limitation imposed by the solvent on the strength of acids and bases in solution. When a base stronger than the solvent's conjugate base is used, it deprotonates the solvent until the base is entirely consumed, making it ineffective against weaker acids. Conversely, an acid stronger than the solvent's conjugate acid protonates the solvent until the acid is depleted, rendering it ineffective against weaker bases. Essentially, the solvent...

Leveling Effect and Non-Aqueous Acid-Base Solutions

Leveling Effect and Non-Aqueous Acid-Base Solutions

This lesson defines the leveling effect in acidic and basic solutions and its role in aqueous and non-aqueous solutions. It is essential to understand the competing nature of various species in a chemical system.
The Leveling Effect of a Solvent
A generic acid (HA) reacts with the generic base (B-) to yield the corresponding conjugate base (A-) and conjugate acid (HB):

Relative Strengths of Conjugate Acid-Base Pairs

Relative Strengths of Conjugate Acid-Base Pairs

Brønsted-Lowry acid-base chemistry is the transfer of protons; thus, logic suggests a relation between the relative strengths of conjugate acid-base pairs. The strength of an acid or base is quantified in its ionization constant, Ka or Kb, which represents the extent of the acid or base ionization reaction. For the conjugate acid-base pair HA / A−, the ionization equilibrium equations and ionization constant expressions are

Titration in Nonaqueous Solvents

Titration in Nonaqueous Solvents

Most acid-base titrations are performed in an aqueous medium. In aqueous titrations, water competes with weaker acids or bases for proton donation or acceptance, leading to ambiguous endpoints in the titration curve. Water also affects the partial ionization of weak acids or bases. For example, water accepts a proton from acetic acid to form hydronium and acetate ions. The hydronium ion formed is a stronger acid than acetic acid, and the acetate ion is a stronger base than water. As a result,...

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Updated: Jul 9, 2026

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method

Isotopic Effect in Double Proton Transfer Process of Porphycene Investigated by Enhanced QM/MM Method

Published on: July 19, 2019

Long-range proton transfer in aqueous Acid-base reactions.

B J Siwick¹, M J Cox, H J Bakker

¹FOM Institute AMOLF, Kruislaan 407, 1098 SJ Amsterdam, The Netherlands.

The Journal of Physical Chemistry. B

|December 11, 2007

Summary

This summary is machine-generated.

Proton transfer in aqueous reactions occurs via diverse hydrogen-bound complexes. Solvent fluctuations and distance-dependent rates govern this essential chemical process, with tunneling playing a minor role.

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Determination of the Gas-phase Acidities of Oligopeptides

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Last Updated: Jul 9, 2026

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Determination of the Gas-phase Acidities of Oligopeptides

Determination of the Gas-phase Acidities of Oligopeptides

Published on: June 24, 2013

Area of Science:

Physical Chemistry
Chemical Kinetics
Spectroscopy

Background:

Proton transfer (PT) is fundamental to many chemical and biological processes.
Understanding PT mechanisms in solution is crucial for various scientific disciplines.

Purpose of the Study:

To elucidate the mechanism of proton transfer in the aqueous reaction between 8-hydroxy-1,3,6-pyrenetrisulfonic acid (HPTS) and acetate.
To investigate the role of solvent and reaction complex structure in proton transfer kinetics.

Main Methods:

Femtosecond mid-infrared laser spectroscopy to probe vibrational resonances.
Analysis of kinetic isotope effects to determine the contribution of tunneling.
Characterization of reaction complexes with varying numbers of intervening water molecules.

Main Results:

Proton transfer occurs within a distribution of hydrogen-bound complexes with 0-5 water molecules separating the acid and base.
A strongly distance-dependent proton transfer rate explains nonexponential kinetics.
A kinetic isotope effect of 1.5 indicates minimal proton tunneling.

Conclusions:

The proton transfer mechanism is best described by the adiabatic picture, emphasizing the role of solvent fluctuations.
Solvent reorganization and hydrogen-bond dynamics are critical for facilitating proton transfer.
The study provides detailed insights into the molecular-level dynamics of proton transfer in solution.