1,3-Cyclohexadiene

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1,3-Cyclohexadiene
1-3-Cyclohexadiene.svg
1,3-cyclohexadiene-3D-balls.png
1,3-cyclohexadiene-3D-vdW.png
Names
IUPAC name
Cyclohexa-1,3-diene
Other names
1,3-Cyclohexadiene, 1,2-Dihydrobenzene, 1,3-CHD
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.008.878
RTECS number GU4702350
Properties
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)
-48.6·10−6 cm3/mol
Hazards
Flammable (F)
R-phrases (outdated) R11
S-phrases (outdated) S9 S16 S29 S33
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).
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Infobox references

1,3-Cyclohexadiene is an organic compound with the formula (CH2)2(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.

Synthesis[edit]

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

1,3-Cyclohexadiene can also be prepared by the electrocyclic reaction from 1,3,5-hexatriene either photochemically or at temperatures above 110 °C.[2]

Reactions[edit]

Useful reactions of this diene are cycloadditions, such as the Diels-Alder reaction.[3]

Conversion of 1,3-cyclohexadiene to benzene + hydrogen is exothermic by about 25 kJ/mol (gas phase).[4][5]

cyclohexane → 1,3-cyclohexadiene + 2 H2 ΔH +231.5 kJ/mol (endothermic)
cyclohexane → benzene + + 3 H2 ΔH +205 kJ (endothermic)
1,3-cyclohexadiene → benzene + H2 ΔH -26.5 kJ (exothermic)

Compared with its isomer 1,4-cyclohexadiene, 1,3-cyclohexadiene is about 8.5 kJ/mol more stable.[6]

Cyclohexadiene and its derivatives form metal-alkene complexes. Illustrative is [C6H10)Fe(CO)3, an orange liquid. This complex reacts with hydride-abstracting reagents to give the cyclohexadienyl derivative [[C6H9)Fe(CO)3]]+.[7]

See also[edit]

References[edit]

  1. ^ John P. Schaefer and Leland Endres (1967). "1,3-Cyclohexadiene". Org. Synth. 47: 31. ; Coll. Vol., 5, p. 285 
  2. ^ Roberts, Stanley (1995). Comprehensive Organic Functional Group Transformations: Synthesis: Carbon with No Attached Heteroatoms. Cambridge, UK: Elsevier Science Ltd. p. 419. ISBN 0080423221. 
  3. ^ 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
  4. ^ US National Institute of Standards and Technology, NIST Chemistry WebBook 1,3-Cyclohexadiene Benzene
  5. ^ J. Sherman The heats of hydrogenation of unsaturated hydrocarbons Journal of the American Oil Chemists' Society; Volume 16, Number 2 / February, 1939
  6. ^ NIST Chemistry WebBook 1,4-Cyclohexadiene
  7. ^ Pearson, Anthony J.; Sun, Huikai (2008). "Cyclohexadieneiron Tricarbonyl". e-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00791.