Woodward–Hoffmann rules

E309911

set of rules in organic chemistry theory in chemistry

The Woodward–Hoffmann rules are fundamental principles in organic chemistry that predict the stereochemistry and feasibility of pericyclic reactions based on orbital symmetry considerations.

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All labels observed (2)

Label	Occurrences
Woodward–Hoffmann rules canonical	5
Woodward–Hoffmann rules for pericyclic reactions	2

How this entity was disambiguated

This entity first appeared as the object of triple T2918396 — 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: Woodward–Hoffmann rules
Context triple: [Robert Burns Woodward, notableWork, Woodward–Hoffmann rules]

A. Franck–Condon principle
The Franck–Condon principle is a rule in molecular spectroscopy that explains the intensity distribution of vibronic transitions by assuming electronic transitions occur much faster than nuclear motion, making vertical transitions between vibrational states most probable.
B. Herzberg–Teller approximation
The Herzberg–Teller approximation is a refinement in molecular spectroscopy that accounts for vibronic coupling by allowing electronic transition dipole moments to depend on nuclear coordinates, explaining intensity in otherwise forbidden transitions.
C. The Nature of the Chemical Bond
The Nature of the Chemical Bond is a landmark chemistry book by Linus Pauling that systematically explains chemical bonding using quantum mechanics and became one of the most influential scientific texts of the 20th century.
D. Longuet-Higgins theorem in molecular symmetry
The Longuet-Higgins theorem in molecular symmetry is a fundamental result in theoretical chemistry that relates molecular symmetry properties to electronic state degeneracies and the occurrence of phenomena such as the Jahn–Teller effect.
E. Born–Oppenheimer approximation
The Born–Oppenheimer approximation is a fundamental method in molecular quantum mechanics that simplifies calculations by treating nuclear motion as much slower than electronic motion, allowing their behaviors to be separated.
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: Woodward–Hoffmann rules
Target entity description: The Woodward–Hoffmann rules are fundamental principles in organic chemistry that predict the stereochemistry and feasibility of pericyclic reactions based on orbital symmetry considerations.

A. Franck–Condon principle
The Franck–Condon principle is a rule in molecular spectroscopy that explains the intensity distribution of vibronic transitions by assuming electronic transitions occur much faster than nuclear motion, making vertical transitions between vibrational states most probable.
B. Herzberg–Teller approximation
The Herzberg–Teller approximation is a refinement in molecular spectroscopy that accounts for vibronic coupling by allowing electronic transition dipole moments to depend on nuclear coordinates, explaining intensity in otherwise forbidden transitions.
C. The Nature of the Chemical Bond
The Nature of the Chemical Bond is a landmark chemistry book by Linus Pauling that systematically explains chemical bonding using quantum mechanics and became one of the most influential scientific texts of the 20th century.
D. Longuet-Higgins theorem in molecular symmetry
The Longuet-Higgins theorem in molecular symmetry is a fundamental result in theoretical chemistry that relates molecular symmetry properties to electronic state degeneracies and the occurrence of phenomena such as the Jahn–Teller effect.
E. Born–Oppenheimer approximation
The Born–Oppenheimer approximation is a fundamental method in molecular quantum mechanics that simplifies calculations by treating nuclear motion as much slower than electronic motion, allowing their behaviors to be separated.
F. None of above. chosen

Statements (48)

Predicate	Object
instanceOf	set of rules in organic chemistry ⓘ theory in chemistry ⓘ
appliesTo	4n electron systems ⓘ 4n+2 electron systems ⓘ cheletropic reactions ⓘ cycloaddition reactions ⓘ electrocyclic reactions ⓘ group transfer reactions ⓘ pericyclic reactions ⓘ sigmatropic rearrangements ⓘ
assumes	concerted reaction mechanism for pericyclic reactions ⓘ
basedOn	molecular orbital theory ⓘ orbital symmetry ⓘ
category	reaction rules in chemistry ⓘ
criterion	conservation of orbital symmetry ⓘ correlation of reactant and product orbitals ⓘ symmetry properties of frontier molecular orbitals ⓘ
determines	allowedness of cycloadditions based on electron count ⓘ stereospecificity of electrocyclic reactions ⓘ
developedBy	Roald Hoffmann ⓘ Robert Burns Woodward ⓘ
distinguishes	thermal and photochemical pericyclic processes ⓘ
field	organic chemistry ⓘ physical organic chemistry ⓘ theoretical chemistry ⓘ
influenced	modern understanding of reaction mechanisms in organic chemistry ⓘ
language	symmetry labels of molecular orbitals ⓘ
predicts	allowed and forbidden pericyclic processes ⓘ conrotatory versus disrotatory electrocyclic ring closures ⓘ conrotatory versus disrotatory electrocyclic ring openings ⓘ feasibility of pericyclic reactions ⓘ stereochemistry of pericyclic reactions ⓘ suprafacial versus antarafacial components in pericyclic reactions ⓘ
publicationYear	1965 ⓘ
recognizedBy	Nobel Prize in Chemistry 1981 for Roald Hoffmann ⓘ
relatedTo	Hückel molecular orbital theory ⓘ correlation diagrams ⓘ frontier molecular orbital theory ⓘ pericyclic reaction mechanism ⓘ
status	fundamental principles in organic chemistry ⓘ
usedIn	analysis of concerted reaction pathways ⓘ design of stereoselective organic syntheses ⓘ
usesConcept	antarafacial interaction ⓘ photochemical reactions ⓘ suprafacial interaction ⓘ symmetry-allowed reactions ⓘ symmetry-forbidden reactions ⓘ thermal reactions ⓘ

How these facts were elicited

Referenced by (7)

Full triples — surface form annotated when it differs from this entity's canonical label.

Robert Burns Woodward → notableWork → Woodward–Hoffmann rules ⓘ

Robert Burns Woodward → knownFor → Woodward–Hoffmann rules ⓘ

this entity surface form: Woodward–Hoffmann rules for pericyclic reactions

Roald Hoffmann → knownFor → Woodward–Hoffmann rules ⓘ

Roald Hoffmann → hasWork → Woodward–Hoffmann rules ⓘ

R. B. Woodward → notableWork → Woodward–Hoffmann rules ⓘ

Roald Safran → notableWork → Woodward–Hoffmann rules ⓘ

Eschenmoser–Claisen rearrangement → governingRules → Woodward–Hoffmann rules ⓘ