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). It is one of two isomers of cyclohexadiene, the other being 1,4-cyclohexadiene.

Cyclohexa-1,3-diene

Names
Preferred IUPAC name Cyclohexa-1,3-diene
Other names 1,3-Cyclohexadiene, 1,2-Dihydrobenzene, 1,3-CHD
Identifiers
CAS Number	592-57-4 Y
3D model (JSmol)	Interactive image
Beilstein Reference	506024
ChEBI	CHEBI:37610 Y
ChemSpider	11117 Y
ECHA InfoCard	100.008.878
EC Number	209-764-1
Gmelin Reference	1657
PubChem CID	11605
RTECS number	GU4702350
UNII	JV5W0EG5BP Y
UN number	1993
CompTox Dashboard (EPA)	DTXSID30862259
InChI InChI=1S/C6H8/c1-2-4-6-5-3-1/h1-4H,5-6H2 Y Key: MGNZXYYWBUKAII-UHFFFAOYSA-N Y 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/cm3
Melting point	−98 °C (−144 °F; 175 K)
Boiling point	80 °C (176 °F; 353 K)
Magnetic susceptibility (χ)	-48.6·10−6 cm3/mol
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H225, H335
Precautionary statements	P210, P233, P240, P241, P242, P243, P261, P271, P280, P303+P361+P353, P304+P340, P312, P370+P378, P403+P233, P403+P235, 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). Y verify (what is YN ?) Infobox references

Synthesis

Cyclohexadiene is prepared by the double 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 (diene)iron tricarbonyl 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]

Occurrence

Cyclohexa-1,3-diene itself is rare in nature, but the cyclohexa-1,3-diene motif is fairly common.^[8] One example is chorismic acid, an intermediate in the shikimic acid pathway. Of the several examples of the terpenoids and terpenes, a prominent example is phellandrene. An unusual derivative is cis-1,2-dihydrocatechol.

Coenzyme A-conjugated to the 2-position of cyclohexadiene-2-carboxylic acid is an intermediate in the biodegradation of aromatic carboxylic acids.^[9]

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. ISBN 978-0471936237.
7. Bennett, M. A.; Huang, T. N.; Matheson, T. W.; Smith, A. K. (1982). "16. (η6 -Hexamethylbenzene)Ruthenium Complexes". (η⁶-Hexamethylbenzene)ruthenium Complexes. Inorganic Syntheses. Vol. 21. pp. 74–78. doi:10.1002/9780470132524.ch16. ISBN 9780470132524.
8. Gribble, G.W. (1991). "Natural Products Containing a Cyclohexane, Cyclohexene, or Cyclohexadiene Subunit". Second Supplements to the 2nd Edition of Rodd's Chemistry of Carbon Compounds. pp. 375–445. doi:10.1016/B978-044453347-0.50066-5. ISBN 978-0-444-53347-0.
9. Porter, A. W.; Young, L. Y. (2014). "Benzoyl-CoA, a Universal Biomarker for Anaerobic Degradation of Aromatic Compounds". Advances in Applied Microbiology. 88: 167–203. doi:10.1016/B978-0-12-800260-5.00005-X. ISBN 978-0-12-800260-5. PMID 24767428.