Limonene (/ˈlɪmənˌiːn/) is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the fragrance and essential oil of citrus fruit peels, taking its name from Italian limone ("lemon").

Limonene

Limonene (R)-isomer
Limonene extracted from orange peel
Names
Pronunciation	/ˈlɪmənˌiːn/ LIM-uh-neen
Preferred IUPAC name 1-Methyl-4-(prop-1-en-2-yl)cyclohex-1-ene
Other names 1-Methyl-4-(1-methylethenyl)cyclohexene 4-Isopropenyl-1-methylcyclohexene p-Menth-1,8-diene Racemic: DL-Limonene; Dipentene
Identifiers
CAS Number	138-86-3 (R/S) Y 5989-27-5 (R) Y 5989-54-8 (S) Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:15384 Y
ChEMBL	ChEMBL449062 (R) Y
ChemSpider	20939 (R/S) Y 388386 (S) Y 389747 (R) Y
ECHA InfoCard	100.004.856
KEGG	D00194 Y
PubChem CID	22311 (R/S) 439250 (S)
UNII	9MC3I34447 (R/S) Y GFD7C86Q1W (R) Y 47MAJ1Y2NE (S) Y
CompTox Dashboard (EPA)	DTXSID2029612
InChI InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4,10H,1,5-7H2,2-3H3 Y Key: XMGQYMWWDOXHJM-UHFFFAOYSA-N Y
SMILES CC1=CCC(CC1)C(=C)C
Properties
Chemical formula	C10H16
Molar mass	136.238 g·mol−1
Appearance	colorless liquid
Odor	Orange
Density	0.8411 g/cm3
Melting point	−74.35 °C (−101.83 °F; 198.80 K)
Boiling point	176 °C (349 °F; 449 K)
Solubility in water	Insoluble
Solubility	Miscible with benzene, chloroform, ether, CS2, and oils soluble in CCl4
Chiral rotation ([α]D)	87–102°
Refractive index (nD)	1.4727
Thermochemistry
Std enthalpy of combustion (ΔcH⦵298)	−6.128 MJ mol−1
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Skin sensitizer / Contact dermatitis – After aspiration, pulmonary oedema, pneumonitis, and death
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H226, H304, H315, H317, H410
Precautionary statements	P210, P233, P235, P240, P241, P242, P243, P261, P264, P272, P273, P280, P301+P330+P331, P302+P352, P303+P361+P353, P304+P340, P312, P333+P313, P362, P370+P378, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)	2 2 0
Flash point	50 °C (122 °F; 323 K)
Autoignition temperature	237 °C (459 °F; 510 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Limonene is a chiral molecule, and most biological sources produce just one enantiomer (isomer). The (+)-isomer, d-limonene, which is the (R)-enantiomer, occurs more commonly in nature in citrus fruit peels, the principal commercial source, from which it is obtained commercially by two primary methods: centrifugal separation and steam distillation. D-limonene is used as a flavoring agent in food manufacturing, in chemical synthesis as a precursor to carvone, and as a renewables-based solvent in cleaning products.

The less common (−)-isomer, l-limonene, which is the (S)-enantiomer, has a piny, turpentine-like odor, and is found in the edible parts of such plants as caraway, dill, and bergamot orange plants.