N/A (found in ylang-ylang, clove, nutmeg; used as synthetic)
Appearance
Colorless to pale yellow clear liquid
Producing Countries
China, India
Pyramid
Heart
Powdery, spiced, faintly sweet — like pressing your nose into a fresh carnation stem. Isoeugenol is the geometrical isomer of eugenol: one double-bond shift converts sharp clove into soft clove-pink.
Warm, powdery-spicy with a distinct carnation identity. Softer and rounder than eugenol — where eugenol is a clove stuck into an orange, isoeugenol is the same clove crushed into talcum powder. Faintly sweet, faintly phenolic, with a smoky balsamic undertow. Less metallic than eugenol, less heavy than methyl isoeugenol. Substantivity is notable: 400 hours at 100% on blotter, outlasting most heart-note materials by an order of magnitude.
Evolution over time
Immediately
Immediately
Sharp powdery-spice burst, distinctly carnation. Sweet phenolic edge, warmer and rounder than eugenol.
After a few hours
After a few hours
The spice mellows into a smooth, balsamic-powdery warmth. Carnation character deepens; the phenolic bite retreats. Smoky, almost woody undertones emerge.
After a few days
After a few days
Persistent powdery-spicy residue — drier, less sweet, still recognisably carnation. Remarkable tenacity for a 164-dalton molecule; traces detectable past 400 hours on blotter.
The Full Story
Isoeugenol (CAS 97-54-1, C₁₀H₁₂O₂, MW 164.20) is a phenylpropanoid — structurally identical to eugenol except that the propenyl side chain is conjugated with the aromatic ring instead of terminal. That single bond migration transforms the sharp, dental-clove bite of eugenol into something rounder: powdery, sweet-spicy, distinctly carnation. The commercial product is a mixture of cis- and trans-isomers in approximately 1:7 ratio; the trans-isomer (mp 33°C) is crystalline and slightly more delicate in odour than the cis (mp 14–18°C, liquid).
Natural occurrence is limited. Betel leaf oil contains roughly 10% isoeugenol; clove bud oil about 1%; ylang-ylang extra up to 0.5%. Industrial supply is almost entirely synthetic: base-catalysed isomerisation of eugenol (from clove oil) using KOH in diethylene glycol at 160–200°C, yielding the thermodynamically favoured trans-isomer. Historically, isoeugenol was also the key intermediate in vanillin manufacture — oxidative cleavage of the propenyl chain gave vanillin directly, though this route has been largely displaced by the guaiacol-glyoxylic acid process.
In perfumery, isoeugenol is the skeleton of carnation accords. Without it, the spicy-floral character of dianthus collapses into generic clove. It bridges eugenol (sharp, medicinal) and methyl isoeugenol (heavier, tuberose-adjacent), occupying a unique position as a warm heart-note modifier. IFRA Amendment 51 (June 2023) restricts isoeugenol to 0.11% in Category 4 (fine fragrance) due to its classification as a skin sensitiser. EU Regulation 2023/1545 lists it among the 26 mandatory-disclosure fragrance allergens: declaration required above 0.001% in leave-on products. IARC Volume 134 (2024) classified isoeugenol as Group 2B — possibly carcinogenic to humans — based on NTP gavage studies showing hepatic tumours in male mice at 300 mg/kg.
Modern formulators working under IFRA budgets often extend isoeugenol with isoeugenyl acetate (CAS 93-29-8, IFRA limit 0.9% Cat 4), which reads softer and slower, or with Methyl Diantilis (CAS 5595-79-9), a non-restricted alternative that approximates the powdery-carnation effect without the sensitisation liability.
The NTP 2-year gavage study (Technical Report 551, 2010) found clear evidence of carcinogenicity in male mice at 300 mg/kg/day — hepatocellular adenomas and carcinomas. IARC subsequently classified isoeugenol as Group 2B (possibly carcinogenic) in Volume 134, published 2024. This makes isoeugenol one of only a handful of common fragrance raw materials to carry both an IFRA restriction and an IARC classification.
Extraction & Chemistry
Extraction method: Industrial production: base-catalysed isomerisation of eugenol. Eugenol (extracted from clove bud oil by steam distillation) is heated with KOH in diethylene glycol or amyl alcohol at 160–200°C for 4–15 hours. The reaction shifts the terminal double bond into conjugation with the ring, producing isoeugenol in approximately 90% conversion. The product is a cis/trans mixture (~1:7); further purification by fractional distillation or crystallisation isolates the trans-isomer if needed. Natural isolates from ylang-ylang or clove oils are not commercially viable given isoeugenol's low concentration in those materials (0.5–1% and ~1% respectively). Betel leaf oil (~10% isoeugenol) is a minor source in South and Southeast Asian markets.
Molecular Formula
C10H12O2
CAS Number
97-54-1
Botanical Name
N/A (found in ylang-ylang, clove, nutmeg; used as synthetic)
IFRA Status
Restricted — known skin sensitizer with strict concentration limits (≤0.02% in leave-on products, IFRA 51st Amendment).
Heart-to-base modifier. Isoeugenol is the structural backbone of carnation reconstructions — it supplies the spicy-powdery floral character that eugenol alone cannot deliver. Functions as a warm bridge between sharp spice notes (cinnamic aldehyde, eugenol) and softer balsamic-floral territories (benzyl benzoate, heliotropin). Essential in classic accord families: carnation, Amber spice blends, certain fougeres, and warm ambery compositions. Synthetic alternatives and extenders: isoeugenyl acetate (CAS 93-29-8) offers a slower, softer version with less sensitisation risk. Methyl Diantilis (CAS 5595-79-9) provides a non-restricted carnation-powder effect for IFRA-compliant formulas. Dihydroeugenol (CAS 2785-87-7) contributes a related but flatter spicy-woody note.
