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alpha-Isomethyl ionone

(Z)-3-methyl-4-(2,6,6-trimethyl-1-cyclohex-2-enyl)but-3-en-2-one

Methyl ionone gamma, alpha-Cetone

Ketone ionone · Ionone ketone · C₁₄H₂₂O

Chemical structure of alpha-Isomethyl ionone
2D structure PubChem / NCI CIR

Chemical info

CAS number CAS
127-51-5
Molecular formula
C₁₄H₂₂O
Molecular weight
206.33 g/mol
Origin
Synthetic
Odor family
Floral
Note
Heart
Aroma
Violet and orris, powdery and warmly woody; softer than the ionones.

History

Methyl ionones are a family of isomers made from citral and methyl ethyl ketone. The alpha-iso form has the most prized odour and is among the EU's original 24 fragrance allergens.

In perfumery

The backbone of orris, violet and powdery accords; widely used in perfume and cosmetics.

Connections

EvokesIris · Orris, Violet

Regulatory status

EU allergen
IFRA 51
Covered by an IFRA Standard (entry "Methyl ionone, mixed isomers"), current version issued at Amendment 49. The Standard text sets the applicable conditions.
EU CosReg
Annex III, entry 90.
EU allergen 2023/1545
One of the original 24 labelled fragrance allergens (Annex III, entry 90). Must be named on the label above 0.001% in leave-on and 0.01% in rinse-off products.

Sources

  1. NCI/CADD Chemical Identifier Resolver, CAS 127-51-5
  2. IFRA Standards Library, Amendments up to 51
  3. Regulation (EC) No 1223/2009, consolidated text of 18.05.2026, Annexes II and III