(E)-3,4,5,6,6-Pentamethylhept-3-en-2-one (CAS 81786-74-5) — Woody Top to middle Note Fragrance Ingredient

ByThe Good Scents
Woody · Green

(E)-3,4,5,6,6-Pentamethylhept-3-en-2-one

CAS 81786-74-5

Origin
synthetic
Note
Top to middle
IFRA
Generally safe
Data as of: Apr 2026

What Is (E)-3,4,5,6,6-Pentamethylhept-3-en-2-one?

(E)-3,4,5,6,6-Pentamethylhept-3-en-2-one is a synthetic fragrance molecule used to create modern, clean scents. You’ll find it in laundry detergents, fabric softeners, and some contemporary perfumes where a fresh, ozonic effect is desired. This ingredient matters because it provides the crisp, metallic freshness that defines many ‘clean linen’ and ‘mountain air’ type fragrances without relying on traditional citrus or aquatic notes.

Safety Profile

GENERALLY SAFE
Generally safeUse with awarenessProfessional use
✓ IFRA compliant for most applications
⚠ Potential skin sensitizer at high concentrations
CAS
81786-74-5
Formula
Mixture
MW
Variable
Odor Family
Woody · Green
Layer 1 · Enthusiast

What Does (E)-3,4,5,6,6-Pentamethylhept-3-en-2-one Smell Like?

This molecule delivers a striking metallic freshness reminiscent of chilled stainless steel with an underlying ozonic character. The top note bursts with a crisp, almost electrical quality like the scent of rain hitting hot pavement. As it evolves, it reveals a clean laundry aspect with subtle woody-amber undertones. The dry-down maintains a persistent freshness, behaving like an ‘invisible’ note that amplifies surrounding accords without dominating them. Its diffusive power creates an expansive sensation of cleanliness and space.

Scent Profile

In Famous Fragrances

Fragrance associations may not reflect actual formulations.

Cool Water(Davidoff, 1988)

Used as a modernizer in the marine accord, providing the crisp metallic edge that makes this fragrance feel freshly laundered.

Light Blue(Dolce & Gabbana, 2001)

Enhances the citrus top notes with an ozonic shimmer, creating the impression of sunlight reflecting off Mediterranean waves.

Layer 2

2D Molecular Structure

(E)-3,4,5,6,6-Pentamethylhept-3-en-2-one

SMILES: CC(\C(C)=C(/C)C(C)=O)C(C)(C)C

Chemistry, Properties & Perfumer Guide

The Chemistry

A branched-chain unsaturated ketone belonging to the alkyl methyl pentenone family. Synthesized via aldol condensation of methyl ethyl ketone with 2,3,4-trimethyl-3-pentenal followed by hydrogenation. The (E)-configuration is essential for optimal odor properties. The molecule’s rigid structure and multiple methyl groups create high volatility and excellent diffusion. The electron-withdrawing carbonyl group interacts strongly with olfactory receptors responsible for detecting fresh/metallic notes.

Physical & Chemical Properties

AppearanceColorless to pale yellow liquid
Boiling PointApprox. 200-220 °C (estimated)

Perfumer Guide

Note Position
Top to middle
Volatility
Medium (1-3 hours)
Blending
Good
ApplicationTypical %RangeNotes
Fine Fragrance0.5-2%Up to 5%Freshness booster
Functional Fragrances1-3%Up to 10%Laundry applications

Classic Accords

Tip: Use at 0.1-0.5% to add crispness to citrus top notes without changing their character.

Alternatives & Comparisons

1
Floralozone CAS 67634-15-5

Offers similar ozonic freshness but with more floral character and better stability in alkaline formulations.

Layer 3

Safety, Regulatory & Sustainability

⚠ Regulatory Disclaimer

General reference only. Consult current IFRA Standards Library before formulating.

IFRA Status

No current IFRA restrictions (as of Amendment 51).

RIFM Assessment

RIFM has reviewed this material and found it safe for use at current industry levels.

Sustainability

As a synthetic material, this molecule is produced through controlled chemical processes with minimal environmental impact. Its high potency means very small quantities are needed in formulations, reducing overall carbon footprint compared to natural alternatives that would require larger harvest volumes.

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References

    Data: PubChem (NIH), PubMed, RIFM, IFRA. Last reviewed: Apr 2026.

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    Ingredient Data Sheet

    CAS 81786-74-5

    Physical Properties

    Molecular Weight182.3 g/mol🔬 PubChem
    LogP (Octanol-Water)3.7🔬 PubChem
    Boiling Point216 °C🔬 EPA CompTox
    Vapor Pressure0.8128 mmHg @ 25°C📊 OPERA
    Flash Point99.9 °C🔬 EPA CompTox
    Involatility Index0.0649💻 Calculated
    log Kp (skin permeability)-1.185💻 Calculated
    SMILESCC(C(=C(C)C(=O)C)C)C(C)(C)C🔬 PubChem

    Volatility & Performance

    Fragrance NoteTop💻 Calculated
    Volatility ClassSlow💻 Calculated
    Persistence Score0.5 / 5💻 Calculated

    Odor & Flavor

    Primary Descriptorsgreenwoody• leffingwell
    Functional Groupsketonealkene💻 RDKit

    Regulatory Status

    IFRA ListedYes — see IFRA Standards for category limits⚖️ IFRA 51
    Data Sources & Attribution
    Physical data: PubChem (NIH/NLM), U.S. EPA CompTox Dashboard, EPA OPERA models, RDKit. Odor & flavor: Arctander (Perfume & Flavor Chemicals), Fenaroli's Handbook of Flavor Ingredients, Leffingwell. Thresholds: van Gemert (Compilations of Odour Threshold Values). Regulatory: IFRA Standards 51st, FEMA GRAS. Trade names: Surburg (Common Fragrance & Flavor Materials). All data compiled and cross-referenced for perfumertools.com.

    Physicochemical Properties

    DTXSID: DTXSID3052563

    Physical Properties

    Molecular Weight 182.307 g/mol🔬 EPA CompTox
    Density 0.852 g/cm^3📊 OPERA
    Boiling Point 226.891 °C📊 OPERA
    Melting Point 16.542 °C📊 OPERA
    Flash Point 93.855 °C📊 OPERA
    Refractive Index 1.44 Dimensionless📊 OPERA
    Molar Volume 217.378 cm^3/mol📊 OPERA

    Partition & Solubility

    LogP (Octanol-Water) 4.214 Log10 unitless📊 OPERA
    LogD (pH 5.5) 4.214 Log10 unitless📊 OPERA
    LogD (pH 7.4) 4.214 Log10 unitless📊 OPERA
    LogKoa (Octanol-Air) 5.56 Log10 unitless📊 OPERA
    Water Solubility 0.001 mol/L📊 OPERA
    Henry's Law Constant 0 atm-m3/mole📊 OPERA

    Transport Properties

    Vapor Pressure 0.309 mmHg📊 OPERA
    Surface Tension 27.785 dyn/cm📊 OPERA

    Molecular Descriptors

    Topological Polar Surface Area 17.07 Ų💻 Computed
    H-Bond Donors 0 count💻 Computed
    H-Bond Acceptors 1 count💻 Computed
    Rotatable Bonds 2 count💻 Computed
    Aromatic Rings 0 count💻 Computed
    Molar Refractivity 57.341 cm^3/mol📊 OPERA
    Polarizability 22.732 Å^3📊 OPERA

    Data Sources:

    🔬 EPA Experimental data from U.S. EPA CompTox Chemicals Dashboard & CTX APIs. 📊 OPERA Predicted using EPA's OPERA QSAR models. 💻 Computed Calculated from SMILES using RDKit.

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