Cyclohexa-1,4-diene

1,4-Cyclohexadiene is an organic compound with the formula C₆H₈. It is a colourless, flammable liquid that is of academic interest as a prototype of a large class of related compounds called terpenoids, an example being γ-terpinene. An isomer of this compound is 1,3-cyclohexadiene.

Cyclohexa-1,4-diene

Skeletal formula with all implicit hydrogen shown, skeletal formula; stereo, skeletal formula with all explicit hydrogens added, all of 1,4-cyclohexadiene
Names
Preferred IUPAC name Cyclohexa-1,4-diene[1]
Other names 1,4-Cyclohexadiene[citation needed] 1,4-Dihydrobenzene[citation needed]
Identifiers
CAS Number	628-41-1 Y
3D model (JSmol)	Interactive image
Abbreviations	1,4-CHDN
Beilstein Reference	1900733
ChEBI	CHEBI:37611 Y
ChemSpider	11838 Y
ECHA InfoCard	100.010.040
EC Number	211-043-1
Gmelin Reference	1656
MeSH	1,4-cyclohexadiene
PubChem CID	12343
UNII	0F8Z5909QZ Y
UN number	3295
CompTox Dashboard (EPA)	DTXSID0060854
InChI InChI=1S/C6H8/c1-2-4-6-5-3-1/h1-2,5-6H,3-4H2 Y Key: UVJHQYIOXKWHFD-UHFFFAOYSA-N Y
SMILES C1C=CCC=C1
Properties
Chemical formula	C6H8
Molar mass	80.130 g·mol−1
Appearance	Colorless liquid
Density	0.847 g cm−3
Melting point	−50 °C; −58 °F; 223 K
Boiling point	82 °C; 179 °F; 355 K
Magnetic susceptibility (χ)	−48.7·10−6 cm3/mol
Refractive index (nD)	1.472
Thermochemistry
Heat capacity (C)	142.2 J K−1 mol−1
Std molar entropy (S⦵298)	189.37 J K−1 mol−1
Std enthalpy of formation (ΔfH⦵298)	63.0–69.2 kJ mol−1
Std enthalpy of combustion (ΔcH⦵298)	−3573.5 – −3567.5 kJ mol−1
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H225, H340, H350, H373
Precautionary statements	P201, P210, P308+P313
NFPA 704 (fire diamond)	2 3 0
Flash point	−7 °C (19 °F; 266 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Synthesis and reactions

In the laboratory, substituted 1,4-cyclohexadienes are synthesized by Birch reduction of related aromatic compounds using an alkali metal dissolved in liquid ammonia and a proton donor such as an alcohol. In this way, over reduction to the fully saturated ring is avoided.

1,4-Cyclohexadiene and its derivatives are easily aromatized, the driving force being the formation of an aromatic ring. The conversion to an aromatic system may be used to trigger other reactions, such as the Bergman cyclization.^[2]