Dibenzocyclobutadiene
[CAS# 259-79-0]

Identification

• Classification: Chemical reagent >> Organic reagent >> Aromatic hydrocarbon reagent
• Name: Dibenzocyclobutadiene
• Synonyms: Cyclobutadibenzene; Biphenylene; Diphenylene; NSC 101862
• Molecular Formula: C₁₂H₈
• Molecular Weight: 152.19
• CAS Registry Number: 259-79-0
• EC Number: 690-155-6
• SMILES: C1=CC=C2C(=C1)C3=CC=CC=C23

Properties

• Density: 1.2±0.1 g/cm³ Calc.^*
• Melting point: 113 - 114 ºC (Expl.)
• Boiling point: 469.9±12.0 ºC 760 mmHg (Calc.)^*
• Flash point: 187.2±14.4 ºC (Calc.)^*
• Index of refraction: 1.697 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS09
• Hazard Statements: H411
• Precautionary Statements: P273-P391-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411

Discovory and Applicatios

Dibenzocyclobutadiene is a polycyclic aromatic hydrocarbon derivative in which a cyclobutadiene core is fused to two benzene rings. It occupies a distinctive place in physical organic chemistry because it combines a formally antiaromatic four-membered ring with stabilizing aromatic benzene units. As a result, the compound has been central to experimental and theoretical studies on aromaticity, antiaromaticity, and the electronic structure of conjugated hydrocarbons.

The conceptual origin of dibenzocyclobutadiene is closely tied to early twentieth century efforts to understand cyclobutadiene itself. Cyclobutadiene was predicted to be highly unstable due to its 4π-electron system, which violates Hückel aromaticity rules. For many decades, cyclobutadiene could not be isolated, and its existence was inferred only indirectly. Chemists therefore explored fused-ring systems in which the cyclobutadiene unit was embedded within larger aromatic frameworks, with the goal of stabilizing the antiaromatic core sufficiently to allow experimental observation. Dibenzocyclobutadiene emerged from this line of inquiry as a theoretically intriguing and experimentally accessible target.

The synthesis and characterization of dibenzocyclobutadiene were milestones in the study of antiaromatic compounds. By fusing the four-membered ring to benzene rings, the overall structure gains partial stabilization through conjugation with the aromatic systems, even though the cyclobutadiene unit itself remains antiaromatic. Experimental studies demonstrated that dibenzocyclobutadiene is still highly reactive and exists only under carefully controlled conditions, but it can be generated and observed spectroscopically. These achievements provided some of the first direct experimental evidence supporting theoretical predictions about antiaromaticity.

From a structural and electronic perspective, dibenzocyclobutadiene exhibits unusual bond length alternation and electronic distribution. The benzene rings retain much of their aromatic character, while the central four-membered ring shows pronounced instability and distortion. This coexistence of aromatic and antiaromatic subunits within a single molecule has made dibenzocyclobutadiene a valuable model system for probing the limits of aromatic stabilization and the consequences of electron delocalization. Studies of its electronic spectra, magnetic properties, and reactivity have contributed significantly to modern concepts of aromaticity.

In terms of application, dibenzocyclobutadiene is not used as a practical material or commercial chemical due to its inherent instability. Its importance lies instead in its role as a fundamental research compound. It has been widely employed in experimental and computational investigations aimed at testing quantum chemical models, validating theoretical descriptions of conjugated systems, and refining criteria for aromatic and antiaromatic behavior. Insights gained from such studies have influenced the broader understanding of conjugated polymers, polycyclic aromatic hydrocarbons, and organic electronic materials.

Dibenzocyclobutadiene has also served as a benchmark compound in the development of spectroscopic and matrix-isolation techniques. Because it is difficult to isolate under normal conditions, researchers have used low-temperature matrices and rapid-generation methods to trap and study the molecule. These experimental strategies have had wider impact, enabling the investigation of other highly reactive or transient organic species.

Overall, dibenzocyclobutadiene represents a landmark compound in physical organic chemistry. Its discovery and study bridged the gap between theoretical predictions and experimental reality for antiaromatic systems. Although it lacks direct practical applications, its contribution to the understanding of electronic structure, aromaticity, and molecular stability has been profound, making it a classic example of how fundamental chemical research can shape core concepts that extend across many areas of chemistry.

References

2025. A Novel Graphyne-Like Carbon Allotrope: 2D Dewar-Anthracyne. Journal of Inorganic and Organometallic Polymers and Materials.
DOI: 10.1007/s10904-025-03947-6

2025. Unlocking colossal storage capacity and energy density of two-dimensional biphenylene oxide for Li-, Na-, and K-ion batteries. Carbon Research.
DOI: 10.1007/s44246-025-00217-5

2025. First-principles insights into biphenylene-based graphynes: promising novel two-dimensional carbon allotropes for thermoelectric applications. Journal of Chemical Sciences.
DOI: 10.1007/s12039-025-02361-2