1. Sesquiterpenes → Woody, Balsamic, Earthy Notes
Sesquiterpenes are volatile C15 terpenoids, the primary contributors to depth, warmth, and longevity of agarwood scent.
Key correlations:
| Sesquiterpene Class | Representative Compounds | Fragrance Notes | Contribution to Quality |
|---|---|---|---|
| Guaiane | α-Guaiene, δ-Guaiene | Woody, dry, slightly sweet | Signature oud aroma, major in Middle Eastern markets |
| Eudesmane | α-Eudesmol, β-Eudesmol | Woody, floral, warm | Adds complexity and soft floral undertones |
| Agarofuran | Agarofuran derivatives | Sweet, balsamic | Enhances richness, smoothness |
| Vetispirane | δ-Vetispirane | Earthy, smoky, dry | Depth, persistence in aged resin |
Takeaway: Sesquiterpenes = base notes, long-lasting and defining “heartwood” aroma.
2. 2-(2-Phenylethyl)chromones → Sweet, Balsamic, Floral Notes
Chromones are semi-volatile heterocyclic compounds, key in soft, lingering sweetness and floral complexity.
Key correlations:
| Chromone | Fragrance Note | Sensory Role |
|---|---|---|
| 6-Methoxy-2-(2-phenylethyl)chromone | Sweet, floral | Enhances softness and elegance |
| 5,6-Dimethoxy-2-(2-phenylethyl)chromone | Balsamic, slightly powdery | Deepens heartwood scent |
| 2-(2-Phenylethyl)chromone derivatives | Complex, warm, resinous | Adds body and aging potential |
Takeaway: Chromones = middle notes, bridging woody base with lighter top notes, contributing to premium aroma.
3. Aromatic Compounds → Floral, Spicy, Sweet Top Notes
Aromatic compounds are generally small, highly volatile molecules, providing the first impression in olfaction.
Key correlations:
| Compound | Fragrance Note | Sensory Role |
|---|---|---|
| 2-Phenylethanol | Rose-like | Fresh, soft floral top note |
| Benzylacetone | Sweet, fruity | Brightens scent, adds liveliness |
| Vanillin | Sweet, creamy | Minor, enhances warmth |
| Cinnamyl alcohol | Spicy, balsamic | Adds subtle spiciness and depth |
Takeaway: Aromatics = top notes, perceived immediately but evaporate quickly.
4. Integrative Fragrance Profile
The perceived fragrance of agarwood is a layered interaction of these three classes:
- Top notes: Aromatic compounds → first impression, light, volatile, fleeting
- Middle notes: Chromones → sweet, balsamic, lingering
- Base notes: Sesquiterpenes → woody, earthy, deep, long-lasting
Visual analogy:
- Think of sesquiterpenes as the foundation, chromones as the heart, and aromatics as the highlight that hits the nose first.
5. Influence of Molecular Ratios
- High sesquiterpene : chromone ratio → Woody-heavy, more masculine oud scent
- Balanced sesquiterpene : chromone ratio → Rich, complex, smooth aroma (premium grade)
- High chromone : sesquiterpene ratio → Softer, sweet, floral; often younger or artificially induced agarwood
- Aromatic content → Intensifies top note, can mask or enhance certain sesquiterpene or chromone notes
Summary Table: Composition vs Fragrance Layer
| Compound Class | Volatility | Typical Aroma Notes | Fragrance Layer | Quality Indicator |
|---|---|---|---|---|
| Sesquiterpenes | Low | Woody, earthy, balsamic | Base | Depth, longevity, premium oud |
| Chromones | Medium | Sweet, floral, resinous | Middle | Complexity, smoothness, aging potential |
| Aromatics | High | Floral, sweet, spicy | Top | Immediate impression, freshness, nuance |