Hexen-2-al (CAS 6728-26-3) — Green Top Note Fragrance Ingredient
Hexen-2-al
CAS 6728-26-3
What Is Hexen-2-al?
Hexen-2-al is a synthetic molecule used in perfumery to create fresh, green, cut-grass effects. It’s found in modern fragrances aiming for naturalistic outdoor accords. This ingredient matters because it provides hyper-realistic ‘just mowed lawn’ notes that natural materials can’t match consistently, allowing perfumers to design scents with photorealistic greenery.
Safety Profile
GENERALLY SAFEWhat Does Hexen-2-al Smell Like?
Hexen-2-al bursts with the piercing green intensity of freshly crushed tomato leaves and broken cucumber stems. The initial effect is almost electric – like snapping a celery stalk underwater. As it evolves, the sharpness softens into a dewy vegetal sweetness reminiscent of pea shoots at dawn, leaving a faint metallic trail like rain on hot pavement. In drydown, it behaves like nature’s ozonic note – not marine, but the charged air before a summer thunderstorm.
In Famous Fragrances
Fragrance associations may not reflect actual formulations.
Jean-Claude Ellena used hexen-2-al to create the illusion of monsoon-drenched vegetation, blending it with pepper and coriander for a hyperrealistic wet garden effect.
Jacques Cavallier employed hexen-2-al to enhance the watery freshness, giving the citrus top notes an extra dimension of crushed green leaves.
2D Molecular Structure
SMILES: CCC\C=C\C=O
Chemistry, Properties & Perfumer Guide
The Chemistry
Hexen-2-al is an unsaturated aldehyde with the molecular formula C6H10O. Its structure features a double bond adjacent to the aldehyde group (α,β-unsaturated aldehyde), which contributes to both its reactivity and distinctive green odor. Industrially produced via oxidation of corresponding alcohols or controlled ozonolysis of appropriate olefins. The trans isomer (2E)-hexenal is naturally occurring in many plants as a defense compound, while the synthetic material used in perfumery is typically an isomer mixture.
Physical & Chemical Properties
| Boiling Point | 47-48 °C at 20 mmHg |
|---|---|
| Density | 0.849 g/cm³ at 20 °C |
| Refractive Index | 1.438-1.448 |
Perfumer Guide
| Application | Typical % | Range | Notes |
|---|---|---|---|
| Fine Fragrance | 0.1-0.5% | Up to 1% | Provides naturalistic green effects |
| Functional Fragrance | 0.01-0.1% | Up to 0.5% | Used in air fresheners for ‘outdoor’ effects |
Classic Accords
Tip: Stabilize with antioxidants to prevent polymerization of the reactive aldehyde group.
Alternatives & Comparisons
Use when a softer, less metallic green effect is desired. Naturally occurring in tea leaves, provides more rounded vegetative character.
Safety, Regulatory & Sustainability
⚠ Regulatory Disclaimer
General reference only. Consult current IFRA Standards Library before formulating.
IFRA Status
Not restricted under current IFRA standards (as of 49th Amendment).
EU Allergen Declaration
Not listed in EU Cosmetics Regulation Annex III allergen declaration requirements.
GHS Classification
RIFM Assessment
RIFM reviewed and deemed safe at current industry usage levels.
Sustainability
Synthetic production avoids agricultural land use and seasonal variability. While not naturally derived, its high potency means minimal quantities are needed, reducing overall environmental impact compared to some natural green materials like galbanum resin.
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References
- Burdock, G.A. (2010). Fenaroli’s Handbook of Flavor Ingredients. CRC Press. ISBN 9781420090866
- Sell, C. (2006). The Chemistry of Fragrances. RSC Publishing. ISBN 9780854048243
Data: PubChem (NIH), PubMed, RIFM, IFRA. Last reviewed: Apr 2026.
Report a data errorPerfumer’s Notes
Odor: [‘apple’, ‘fresh’, ‘fruity’, ‘grassy’, ‘green’, ‘leafy’, ‘pungent’, ‘vegetable’]
MW: 98.14
LogP: 1.5
Ingredient Data Sheet
CAS 6728-26-3Physical Properties
| Molecular Weight | 98.14 g/mol🔬 PubChem |
| LogP (Octanol-Water) | 1.5🔬 PubChem |
| Boiling Point | 47 °C🔬 EPA CompTox |
| Vapor Pressure | 6.6 mmHg @ 25°C📊 OPERA |
| Flash Point | 35 °C🔬 EPA CompTox |
| Involatility Index | 0.718💻 Calculated |
| log Kp (skin permeability) | -2.234💻 Calculated |
| SMILES | CCCC=CC=O🔬 PubChem |
Volatility & Performance
| Fragrance Note | Top💻 Calculated |
| Volatility Class | Moderate💻 Calculated |
| Persistence Score | 0.5 / 5💻 Calculated |
Odor & Flavor
| Primary Descriptors | applefreshfruitygrassygreenleafypungent• leffingwell |
| Functional Groups | aldehydealkene💻 RDKit |
| “Powerful green-fruity, pungent vegetable-like odor, pungent in high concentrations, almost acrylic-sharp, but pleasant fruity and fresh-green in dilutions below 0.1%.”📖 Arctander | |
Flavor Notes (Arctander)
| “Almost insoluble in water, soluble in alcohol, Propylene glycol and most perfume and flavor oils. This aldehyde finds even more use in flavor compositions, particularly in Strawberry, Banana, Apple, Apricot, Plum, Pear and many berry or fruit complexes. In Orange flavors it may introduce a much want”📖 Arctander |
Sensory Thresholds
| Odor Detection Threshold | 0.8424 ppm (n=18)📖 van Gemert |
Regulatory Status
| IFRA Listed | Yes — see IFRA Standards for category limits⚖️ IFRA 51 |
| FEMA Number | FEMA 2560⚖️ FEMA GRAS |
| GRAS Status | Generally Recognized as Safe⚖️ FEMA GRAS |
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: DTXSID1041425
Physical Properties
| Molecular Weight | 98.145 g/mol🔬 EPA CompTox |
| Density | 0.846 g/cm^3🔬 EPA CTX |
| Boiling Point | 146.875 °C🔬 EPA CTX |
| Melting Point | -55.6 °C🔬 EPA CTX |
| Flash Point | 35.075 °C🔬 EPA CTX |
| Refractive Index | 1.422 Dimensionless📊 OPERA |
| Molar Volume | 118.509 cm^3/mol📊 OPERA |
Partition & Solubility
| LogP (Octanol-Water) | 1.58 Log10 unitless🔬 EPA CTX |
| LogD (pH 5.5) | 1.139 Log10 unitless📊 OPERA |
| LogD (pH 7.4) | 1.139 Log10 unitless📊 OPERA |
| LogKoa (Octanol-Air) | 3.65 Log10 unitless📊 OPERA |
| Water Solubility | 0.054 mol/L🔬 EPA CTX |
| Henry's Law Constant | 0 atm-m3/mole🔬 EPA CTX |
Transport Properties
| Vapor Pressure | 6.6 mmHg🔬 EPA CTX |
| Viscosity | 0.607 cP📊 OPERA |
| Surface Tension | 24.845 dyn/cm📊 OPERA |
| Thermal Conductivity | 145.745 mW/(m*K)📊 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 | 3 count💻 Computed |
| Aromatic Rings | 0 count💻 Computed |
| Molar Refractivity | 30.091 cm^3/mol📊 OPERA |
| Polarizability | 11.929 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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