(E)-1,2-Diphenylethene
[CAS 103-30-0]

Identification

• Classification: Chemical reagent >> Organic reagent >> Aromatic hydrocarbon reagent
• Name: (E)-1,2-Diphenylethene
• Synonyms: (E)-1,2-Diphenylethylene; (E)-Stilbene; 1,1'-(1E)-1,2-Ethenediylbis[benzene]; NSC 2069; trans-1,2-Diphenylethene; trans-1,2-Diphenylethylene; trans-Diphenylethene; trans-Stilbene
• Molecular Formula: C₁₄H₁₂
• Molecular Weight: 180.25
• CAS Registry Number: 103-30-0
• EC Number: 203-098-5
• SMILES: C1=CC=C(C=C1)/C=C/C2=CC=CC=C2

Properties

• Density: 1.0±0.1 g/cm³ Calc.^*, 0.97 g/mL (Expl.)
• Melting point: 123 - 125 °C (Expl.)
• Boiling point: 307.0 °C 760 mmHg (Calc.)^*, 306.1 - 308.1 °C (Expl.)
• Flash point: 128.5±9.7 °C (Calc.)^*
• Index of refraction: 1.659 (Calc.)^*

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

Safety Data

• Hazard Symbols: GHS07;GHS09 Warning
• Risk Statements: H302-H319-H411
• Safety Statements: P264-P264+P265-P270-P273-P280-P301+P317-P305+P351+P338-P330-P337+P317-P391-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Eye irritation	Eye Irrit.	2	H319
Chronic hazardous to the aquatic environment	Aquatic Chronic	2	H411
Skin sensitization	Skin Sens.	1	H317

• Transport Information: UN 3077

Discovery and Applications

(E)-1,2-Diphenylethene, commonly known as trans-stilbene, is an aromatic hydrocarbon belonging to the stilbene family. It consists of two phenyl rings connected by a carbon–carbon double bond in the trans (E) configuration. The compound is an important structural motif in organic chemistry and serves as a starting material, synthetic intermediate, and model compound for studies of stereochemistry, photochemistry, and conjugated π-systems.

Structurally, the molecule contains two benzene rings linked through an ethene bridge (–CH=CH–). Each carbon atom of the double bond is bonded to one phenyl group and one hydrogen atom. The designation (E) indicates that the two phenyl groups are located on opposite sides of the carbon–carbon double bond according to the Cahn–Ingold–Prelog priority rules. This trans arrangement minimizes steric interactions between the bulky aromatic rings, making the (E)-isomer thermodynamically more stable than the corresponding (Z)-isomer.

The benzene rings are aromatic and each contains six delocalized π-electrons distributed over a planar six-membered ring. These aromatic systems are connected to the central alkene through conjugation, allowing partial delocalization of π-electrons across the entire molecule. Although complete coplanarity of both phenyl rings with the double bond is not always achieved because of steric effects, the molecule possesses an extended conjugated π-system that contributes to its characteristic electronic and optical properties.

The carbon atoms of the central double bond are sp²-hybridized and adopt trigonal planar geometry. Rotation about the carbon–carbon double bond is restricted, preserving the geometric configuration. This restricted rotation is responsible for the existence of distinct (E)- and (Z)-stereoisomers.

From an electronic perspective, conjugation between the alkene and the aromatic rings lowers the overall energy of the π-system compared with isolated double bonds. The extended delocalization also results in characteristic ultraviolet absorption arising from π→π* electronic transitions. The molecule is therefore widely used as a model compound in studies of conjugated organic systems.

Physicochemically, (E)-1,2-diphenylethene is predominantly nonpolar. The aromatic rings constitute most of the molecular surface, and the molecule contains no strongly polar functional groups capable of hydrogen bonding. Consequently, it exhibits low water solubility but dissolves readily in many nonpolar and moderately polar organic solvents.

Chemically, the carbon–carbon double bond represents the principal reactive site. It undergoes reactions typical of alkenes, including catalytic hydrogenation to produce 1,2-diphenylethane and electrophilic addition reactions under appropriate conditions. Because the double bond is conjugated with two aromatic rings, its reactivity differs somewhat from that of simple alkenes, with conjugation providing additional stabilization.

One of the most characteristic properties of trans-stilbene is its photochemical behavior. Upon irradiation with ultraviolet light, the molecule can undergo photoisomerization to form the corresponding (Z)-1,2-diphenylethene. This reversible isomerization has made stilbene a classic model system for investigating photochemical reactions and excited-state molecular dynamics.

The aromatic rings generally retain their chemical stability under ordinary conditions, although they can undergo electrophilic aromatic substitution reactions typical of benzene derivatives. The conjugated framework also allows participation in certain oxidation reactions, leading to cleavage or formation of oxygenated products under sufficiently strong oxidizing conditions.

Overall, (E)-1,2-diphenylethene is a conjugated aromatic alkene composed of two phenyl rings connected by a trans-configured carbon–carbon double bond. Its rigid stereochemistry, extended π-conjugation, and characteristic photochemical isomerization make it an important representative of the stilbene family in organic chemistry and materials research.

References

2026. Ultra-Violet Induced Biochemical Changes in an Invasive Weed and their Implications for Plant-Biocontrol Agent Interactions. Journal of Chemical Ecology.
DOI: 10.1007/s10886-026-01699-2

2026. Needle and bark specialised metabolites of Norway spruce depend on forest site type and stand composition. Plant Ecology.
DOI: 10.1007/s11258-026-01619-0

2026. Proximate analysis, phytochemical profiling and GC–MS characterization of bioactive compounds of ethanolic extract and oil of Arachis hypogaea. Discover Plants.
DOI: 10.1007/s44372-026-00501-7