1,3-Cyclohexadiene

1,3-Cyclohexadiene

Names
IUPAC name Cyclohexa-1,3-diene
Other names 1,3-Cyclohexadiene, 1,2-Dihydrobenzene, 1,3-CHD
Identifiers
CAS Registry Number	592-57-4 Y
ChEBI	CHEBI:37610 Y
ChemSpider	11117 Y
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
Jmol-3D images	Image
PubChem	11605
RTECS number	GU4702350
SMILES C\1=C\C=C/CC/1
Properties
Chemical formula	C6H8
Molar mass	80.13 g/mol
Appearance	Colourless liquid
Density	0.841 g/cm3
Melting point	−98 °C (−144 °F; 175 K)
Boiling point	80 °C (176 °F; 353 K)
Hazards
EU classification	Flammable (F)
R-phrases	R11
S-phrases	S9 S16 S29 S33
Flash point	26 °C (79 °F; 299 K) c.c.
Except where noted otherwise, data is 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

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

1,3-Cyclohexadiene can be used as a hydrogen donor in transfer hydrogenation, since its conversion to benzene + hydrogen is exothermic by about 20 kJ/mol (gas phase). ^[3][4]

cyclohexane → 1,3-cyclohexadiene + 2 H₂ ΔH +224 kJ/mol (endothermic)

cyclohexane → benzene + + 3 H₂ ΔH +205 kJ (endothermic)

1,3-cyclohexadiene → benzene + H₂ ΔH -19 kJ (exothermic)

Compared with its isomer, 1,4-cyclohexadiene, 1,3-cyclohexadiene is about 1.6 kJ/mol less stable.^[5]

See also

• 1,4-Cyclohexadiene
• Cyclohexene

References