Hammett sigma constants
E743332
Hammett sigma constants are substituent constants used in physical organic chemistry to quantify the electronic effects of substituents on reaction rates and equilibria in aromatic systems.
All labels observed (4)
| Label | Occurrences |
|---|---|
| Hammett sigma constant | 1 |
| Hammett sigma constants canonical | 1 |
| Hammett sigma meta constant | 1 |
| Hammett sigma para constant | 1 |
How this entity was disambiguated
This entity first appeared as the object of triple T8558023 — 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 sigma constants Context triple: [Louis P. Hammett, notableConcept, Hammett sigma constants]
-
A.
Mulliken electronegativity scale
The Mulliken electronegativity scale is a quantitative measure of an atom’s tendency to attract electrons, defined as the average of its ionization energy and electron affinity.
-
B.
Extended Hückel method
The Extended Hückel method is a semi-empirical quantum chemistry approach developed by Roald Hoffmann to approximate molecular electronic structure and bonding using simplified orbital interactions.
-
C.
Carothers equation
The Carothers equation is a fundamental relation in polymer chemistry that links the average degree of polymerization to the extent of reaction in step-growth polymerizations.
-
D.
Westheimer rules in physical organic chemistry
Westheimer rules in physical organic chemistry are empirical guidelines that relate molecular structure and substituent effects to reaction rates and mechanisms, helping to rationalize and predict reactivity patterns.
-
E.
Karplus equation for NMR coupling constants
The Karplus equation for NMR coupling constants is an empirical relationship that links three-bond scalar coupling values between nuclei to the dihedral angle between them, enabling the determination of molecular conformations from NMR data.
- 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 sigma constants Target entity description: Hammett sigma constants are substituent constants used in physical organic chemistry to quantify the electronic effects of substituents on reaction rates and equilibria in aromatic systems.
-
A.
Mulliken electronegativity scale
The Mulliken electronegativity scale is a quantitative measure of an atom’s tendency to attract electrons, defined as the average of its ionization energy and electron affinity.
-
B.
Extended Hückel method
The Extended Hückel method is a semi-empirical quantum chemistry approach developed by Roald Hoffmann to approximate molecular electronic structure and bonding using simplified orbital interactions.
-
C.
Carothers equation
The Carothers equation is a fundamental relation in polymer chemistry that links the average degree of polymerization to the extent of reaction in step-growth polymerizations.
-
D.
Westheimer rules in physical organic chemistry
Westheimer rules in physical organic chemistry are empirical guidelines that relate molecular structure and substituent effects to reaction rates and mechanisms, helping to rationalize and predict reactivity patterns.
-
E.
Karplus equation for NMR coupling constants
The Karplus equation for NMR coupling constants is an empirical relationship that links three-bond scalar coupling values between nuclei to the dihedral angle between them, enabling the determination of molecular conformations from NMR data.
- F. None of above. chosen
Statements (49)
| Predicate | Object |
|---|---|
| instanceOf |
linear free energy relationship parameter
ⓘ
physical organic chemistry parameter ⓘ substituent constant ⓘ |
| appliesPrimarilyTo | substituents on aromatic rings ⓘ |
| appliesTo |
aromatic systems
ⓘ
substituted benzoic acids ⓘ |
| assumes | linear free energy relationship ⓘ |
| characterizes |
meta substituent effects
ⓘ
para substituent effects ⓘ |
| definedRelativeTo | unsubstituted benzoic acid ⓘ |
| developedInField | physical organic chemistry ⓘ |
| domain |
chemistry
ⓘ
organic chemistry ⓘ |
| hasExtension |
σ+ constants
ⓘ
σI constants ⓘ σR constants ⓘ σ− constants ⓘ |
| hasVariant |
Hammett sigma meta constant
ⓘ
linked to:
Hammett sigma constants
Hammett sigma para constant ⓘ
linked to:
Hammett sigma constants
σm ⓘ σp ⓘ |
| introducedBy |
Louis Plack Hammett
ⓘ
linked to:
Louis P. Hammett
|
| introducedIn | 1937 ⓘ |
| namedAfter |
Louis Plack Hammett
ⓘ
linked to:
Louis P. Hammett
|
| negativeValuesIndicate | electron-donating substituents ⓘ |
| positiveValuesIndicate | electron-withdrawing substituents ⓘ |
| quantifies |
electronic effects of substituents
ⓘ
inductive effects ⓘ resonance effects ⓘ |
| referenceReaction | ionization of substituted benzoic acids ⓘ |
| referenceSolvent | water ⓘ |
| referenceTemperature | 25 °C ⓘ |
| relatedConcept |
Taft steric constants
ⓘ
Yukawa–Tsuno equation ⓘ |
| relatedTo |
Hammett equation
ⓘ
reaction constant ρ ⓘ |
| symbol | σ ⓘ |
| usedFor |
design of organic molecules
ⓘ
mechanistic interpretation of substituent effects ⓘ quantitative structure–reactivity relationships ⓘ |
| usedIn |
correlation of equilibrium constants
ⓘ
correlation of reaction rates ⓘ linear free energy relationship analysis ⓘ physical organic chemistry ⓘ |
| usedToCorrelate | substituent effects across different reactions ⓘ |
| usedToEstimate |
equilibrium constants
ⓘ
reaction rate constants ⓘ |
| usedWith | reaction constant ρ in Hammett equation ⓘ |
| zeroPointReference | hydrogen substituent ⓘ |
How these facts were elicited
The pipeline generated the facts above by prompting gpt-5.1 with this entity's name + description and the instruction below.
Instruction
You are a knowledge base construction expert. Given a subject entity and a description of it, return factual statements that you know for the subject as a JSON list of dictionaries(triples), where keys must be "subject", "predicate" and "object". The number of facts may be very high, between 25 to 50 or more, for very popular subjects. For less popular subjects, the number of facts can be very low, like 5 or 10. # Requirements - If you don't know the subject at all, return an empty list. - If the subject is not a named entity, return an empty list. - Include at least one triple where predicate is "instanceOf". - Do not get too wordy. - Separate several objects into multiple triples with one object.
Input
Subject: Hammett sigma constants Description of subject: Hammett sigma constants are substituent constants used in physical organic chemistry to quantify the electronic effects of substituents on reaction rates and equilibria in aromatic systems.
Referenced by (4)
Full triples — surface form annotated when it differs from this entity's canonical label.
linked to: Hammett sigma constants
linked to: Hammett sigma constants
linked to: Hammett sigma constants