Cyclohexa-1,3-diene

Cyclohexa-1,3-diene is an organic compound with the formula (C₂H₄)(CH)₄. It is a colorless, flammable liquid. Its refractive index is 1.475 (20 °C, D). A naturally occurring derivative of 1,3-cyclohexadiene is terpinene, a component of pine oil.

Cyclohexa-1,3-diene

Names
IUPAC name Cyclohexa-1,3-diene
Other names 1,3-Cyclohexadiene, 1,2-Dihydrobenzene, 1,3-CHD
Identifiers
CAS Number	592-57-4
3D model (JSmol)	Interactive image
Beilstein Reference	506024
ChEBI	CHEBI:37610
ChemSpider	11117
ECHA InfoCard	100.008.878
EC Number	209-764-1
Gmelin Reference	1657
PubChem CID	11605
RTECS number	GU4702350
UNII	JV5W0EG5BP
UN number	1993
CompTox Dashboard (EPA)	DTXSID30862259
InChI InChI=1S/C6H8/c1-2-4-6-5-3-1/h1-4H,5-6H2 Key: MGNZXYYWBUKAII-UHFFFAOYSA-N InChI=1/C6H8/c1-2-4-6-5-3-1/h1-4H,5-6H2 Key: MGNZXYYWBUKAII-UHFFFAOYAH
SMILES C\1=C\C=C/CC/1
Properties
Chemical formula	C6H8
Molar mass	80.13 g/mol
Appearance	Colorless liquid
Density	0.841 g/cm^3
Melting point	−98 °C (−144 °F; 175 K)
Boiling point	80 °C (176 °F; 353 K)
Magnetic susceptibility (χ)	-48.6·10^−6 cm^3/mol
Hazards
GHS pictograms
GHS Signal word	Danger
GHS hazard statements	H225, H335
GHS precautionary statements	P210, P233, P240, P241, P242, P243, P261, P271, P280, P303+361+353, P304+340, P312, P370+378, P403+233, P403+235, P405, P501
Flash point	26 °C (79 °F; 299 K) c.c.
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
verify (what is  ?)
Infobox references

Synthesis

Cyclohexadiene is prepared by the dehydrobromination of 1,2-dibromocyclohexane:[1]

(CH₂)₄(CHBr)₂ + 2 NaH → (CH₂)₂(CH)₄ + 2 NaBr + 2 H₂

Reactions

Useful reactions of this diene are cycloadditions, such as the Diels-Alder reaction.[2]

Conversion of cyclohexa-1,3-diene to benzene + hydrogen is exothermic by about 25 kJ/mol in the gas phase.[3][4]

cyclohexane → cyclohexa-1,3-diene + 2 H₂ (ΔH = +231.5 kJ/mol; endothermic)

cyclohexane → benzene + 3 H₂ (ΔH = +205 kJ/mol; endothermic)

cyclohexa-1,3-diene → benzene + H₂ (ΔH = -26.5 kJ/mol; exothermic)

Compared with its isomer cyclohexa-1,4-diene, cyclohexa-1,3-diene is about 1.6 kJ/mol more stable.[5]

Cyclohexadiene and its derivatives form metal-alkene complexes. Illustrative is [C₆H₈)Fe(CO)₃], an orange liquid. This complex reacts with hydride-abstracting reagents to give the cyclohexadienyl derivative [C₆H₇)Fe(CO)₃]⁺.[6] Cyclohexadienes react with ruthenium trichloride to give (Benzene)ruthenium dichloride dimer.[7]

See also

• 1,4-Cyclohexadiene
• Cyclohexene

References

1. Schaefer, John P.; Endres, Leland (1967). "1,3-Cyclohexadiene". Organic Syntheses. 47: 31. doi:10.15227/orgsyn.047.0031.
2. Sanjeeva Rao Guppi, George A. O'Doherty, "1,3-Cyclohexadiene" Encyclopedia of Reagents for Organic Synthesis, 2008 John Wiley & Sons. doi:10.1002/047084289X.rn00921
3. US National Institute of Standards and Technology, NIST Chemistry WebBook 1,3-Cyclohexadiene Benzene
4. J. Sherman The heats of hydrogenation of unsaturated hydrocarbons Archived 2011-07-14 at the Wayback Machine Journal of the American Oil Chemists' Society; Volume 16, Number 2 / February, 1939
5. NIST Chemistry WebBook 1,4-Cyclohexadiene
6. Pearson, Anthony J.; Sun, Huikai (2008). "Cyclohexadieneiron Tricarbonyl". e-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00791.
7. Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A. K. (1982). "(η⁶-Hexamethylbenzene)ruthenium Complexes". Inorganic Syntheses. 21: 74–78. doi:10.1002/9780470132524.ch16.