Phellandrenes

α-Phellandrene β-Phellandrene
Names
IUPAC names (α): 2-Methyl-5-(propan-2-yl)cyclohexa-1,3-diene (β): 3-Methylidene-6-(propan-2-yl)cyclohex-1-ene
Identifiers
CAS Number	(α): 99-83-2 Y (β): 555-10-2 Y (−)-(α): 4221-98-1 Y (+)-(α): 2243-33-6 Y
3D model (JSmol)	(α): Interactive image (β): Interactive image (−)-(α): Interactive image (+)-(α): Interactive image
ChEBI	(β): CHEBI:48741 (−)-(α): CHEBI:301 (+)-(α): CHEBI:367 (−)-(β): CHEBI:129 (+)-(β): CHEBI:53
ChemSpider	(α): 7180 N (β): 10669 N
ECHA InfoCard	100.014.121
EC Number	(α): 202-792-5 (β): 209-081-9 (−)-(α): 224-167-6
KEGG	(−)-(α): C09875 (+)-(α): C11391 (−)-(β): C11392 (+)-(β): C09877
PubChem CID	(α): 7460 (β): 11142 (−)-(α): 442482 (+)-(α): 443160 (−)-(β): 443161
UNII	(α): 49JV13XE39 Y (β): 2KK225M001 Y (−)-(α): 56UV8X65K0 Y (+)-(α): E45FS72C5K Y
CompTox Dashboard (EPA)	(α): DTXSID8051673
InChI (α): InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4-6,8,10H,7H2,1-3H3 Key: OGLDWXZKYODSOB-UHFFFAOYSA-N (β): InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4,6,8,10H,3,5,7H2,1-2H3 Key: LFJQCDVYDGGFCH-UHFFFAOYSA-N (−)-(α): InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4-6,8,10H,7H2,1-3H3/t10-/m1/s1 Key: OGLDWXZKYODSOB-SNVBAGLBSA-N (+)-(α): InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4-6,8,10H,7H2,1-3H3/t10-/m0/s1 Key: OGLDWXZKYODSOB-JTQLQIEISA-N
SMILES (α): CC1=CCC(C=C1)C(C)C (β): CC(C)C1CCC(=C)C=C1 (−)-(α): CC1=CC[C@@H](C=C1)C(C)C (+)-(α): CC1=CC[C@H](C=C1)C(C)C
Properties[1]
Chemical formula	C10H16
Molar mass	136.24 g/mol
Appearance	Colorless oil (α and β)
Density	α: 0.846 g/cm3 β: 0.85 g/cm3
Boiling point	α: 171-172 °C β: 171-172 °C
Solubility in water	Insoluble (α and β)
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H226, H304
Precautionary statements	P210, P233, P240, P241, P242, P243, P280, P301+P310, P303+P361+P353, P331, P370+P378, P403+P235, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Phellandrenes are a pair of organic compounds that have a similar molecular structure and similar chemical properties. α-Phellandrene and β-phellandrene are cyclic monoterpenes and are double-bond isomers. In α-phellandrene, both double bonds are endocyclic and in β-phellandrene, one of them is exocyclic. Both are insoluble in water, but miscible with diethyl ether.

α-Phellandrene was named after Eucalyptus phellandra, now called Eucalyptus radiata, from which it can be isolated.^[2] It is also a constituent of the essential oil of Eucalyptus dives.^[3] β-Phellandrene has been isolated from the oil of water fennel and Canada balsam oil.

The phellandrenes are used in fragrances because of their pleasing aromas. The odor of β-phellandrene has been described as peppery-minty and slightly citrusy.

The α-phellandrene isomer can form hazardous and explosive peroxides on contact with air at elevated temperatures.^[4]

Biosynthesis

The biosynthesis of phellandrene begins with dimethylallyl pyrophosphate and isopentenyl pyrophosphate condensing in an S_N1 reaction to form geranyl pyrophosphate. The resultant monoterpene undergoes cyclization to form a menthyl cationic species. A hydride shift then forms an allylic carbocation. Finally, an elimination reaction occurs at one of two positions, yielding either α-phellandrene or β-phellandrene.^[5]