Hammett equation

E743329

linear free-energy relationship physical organic chemistry concept quantitative structure–reactivity relationship

The Hammett equation is a fundamental linear free-energy relationship in physical organic chemistry that quantitatively correlates reaction rates and equilibria with the electronic effects of substituents on aromatic compounds.

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All labels observed (2)

Label	Occurrences
Hammett equation canonical	5
Taft equation	1

How this entity was disambiguated

This entity first appeared as the object of triple T8558007 — resolving that mention is where its identity was fixed. The disambiguator weighed these candidate entities and picked the highlighted one (or “None”, minting a new entity). This is how homonymy is resolved: the same surface form can point to different entities.

NED1 Entity disambiguation (via context triple) gpt-5-mini-2025-08-07

Target entity: Hammett equation
Context triple: [Louis P. Hammett, knownFor, Hammett equation]

A. Arrhenius equation
The Arrhenius equation is a fundamental formula in physical chemistry that relates the rate of a chemical reaction to temperature through an exponential dependence on activation energy.
B. Hill equation
The Hill equation is a mathematical expression used in biochemistry and physiology to describe how the binding of ligands to macromolecules or the response to a drug depends on ligand concentration, often capturing cooperative binding behavior.
C. Eyring equation
The Eyring equation is a fundamental expression in chemical kinetics that relates reaction rates to temperature using transition state theory, providing insight into activation parameters such as enthalpy and entropy.
D. Nernst equation
The Nernst equation is a fundamental electrochemistry formula that relates the reduction potential of a half-cell to the standard electrode potential, temperature, and activities (or concentrations) of the chemical species involved.
E. Randles–Ševčík equation
The Randles–Ševčík equation is a fundamental electrochemical relationship that links peak current in cyclic voltammetry to the concentration and diffusion coefficient of a redox-active species.
F. None of above. chosen
G. Unsure - the case is ambiguous/there is not enough information to decide.

NED2 Entity disambiguation (via description) gpt-5-mini-2025-08-07

Target entity: Hammett equation
Target entity description: The Hammett equation is a fundamental linear free-energy relationship in physical organic chemistry that quantitatively correlates reaction rates and equilibria with the electronic effects of substituents on aromatic compounds.

A. Arrhenius equation
The Arrhenius equation is a fundamental formula in physical chemistry that relates the rate of a chemical reaction to temperature through an exponential dependence on activation energy.
B. Hill equation
The Hill equation is a mathematical expression used in biochemistry and physiology to describe how the binding of ligands to macromolecules or the response to a drug depends on ligand concentration, often capturing cooperative binding behavior.
C. Eyring equation
The Eyring equation is a fundamental expression in chemical kinetics that relates reaction rates to temperature using transition state theory, providing insight into activation parameters such as enthalpy and entropy.
D. Nernst equation
The Nernst equation is a fundamental electrochemistry formula that relates the reduction potential of a half-cell to the standard electrode potential, temperature, and activities (or concentrations) of the chemical species involved.
E. Randles–Ševčík equation
The Randles–Ševčík equation is a fundamental electrochemical relationship that links peak current in cyclic voltammetry to the concentration and diffusion coefficient of a redox-active species.
F. None of above. chosen

Statements (48)

Predicate	Object
instanceOf	linear free-energy relationship ⓘ physical organic chemistry concept ⓘ quantitative structure–reactivity relationship ⓘ
appliesBestTo	meta- and para-substituted benzoic acid derivatives ⓘ
appliesTo	benzoic acid derivatives ⓘ reactions involving aromatic substituents ⓘ substituted aromatic compounds ⓘ
assumes	constant reaction mechanism across substituents ⓘ dominant electronic effects of substituents ⓘ
basedOn	reference reactions of substituted benzoic acids ⓘ
category	Chemical kinetics ⓘ Physical organic chemistry theories ⓘ
correlates	electronic effects of substituents ⓘ equilibrium constants ⓘ reaction rates ⓘ
describes	linear relationship between log(K) and sigma ⓘ linear relationship between log(k) and sigma ⓘ
developedBy	Louis Plack Hammett ⓘ linked to: Louis P. Hammett
field	organic chemistry ⓘ physical organic chemistry ⓘ
hasKeyConcept	linear correlation between structure and free energy changes ⓘ
hasMathematicalForm	log(K/K0) = ρσ ⓘ log(k/k0) = ρσ ⓘ
hasVariant	dual-parameter Hammett relationships ⓘ sigma-minus (σ⁻) constants ⓘ sigma-plus (σ⁺) constants ⓘ
introducedIn	1937 ⓘ
involvesEffect	inductive effects ⓘ resonance effects ⓘ
involvesQuantity	equilibrium constant K ⓘ rate constant k ⓘ standard free energy change ΔG° via K ⓘ
lessAccurateFor	strongly resonance-interacting ortho substituents ⓘ
namedAfter	Louis Plack Hammett ⓘ linked to: Louis P. Hammett
quantifies	sensitivity of a reaction to substituent electronic effects ⓘ
relatedTo	Taft equation ⓘ Yukawa–Tsuno equation ⓘ linear free-energy relationships ⓘ
relates	reaction constant rho to sensitivity to substituent effects ⓘ substituent constant sigma to reactivity ⓘ
usedFor	analyzing substituent effects ⓘ correlating equilibrium constants ⓘ predicting relative reaction rates ⓘ
usedIn	design of organic molecules with tuned reactivity ⓘ mechanistic studies of organic reactions ⓘ structure–reactivity correlation studies ⓘ
usesParameter	Hammett sigma constant ⓘ linked to: Hammett sigma constants reaction constant rho ⓘ