3a,4,5,6,7,7a-Hexahydromethoxy-4,7-methano-1H-indene (isomer unspecified) (CAS 27135-90-6) — Woody Middle to Base Note Fragrance Ingredient

ByThe Good Scents
Woody · Balsamic

3a,4,5,6,7,7a-Hexahydromethoxy-4,7-methano-1H-indene (isomer unspecified)

CAS 27135-90-6

Origin
synthetic
Note
Middle to Base
IFRA
Use with awareness
Data as of: Apr 2026

What Is 3a,4,5,6,7,7a-Hexahydromethoxy-4,7-methano-1H-indene (isomer unspecified)?

3a,4,5,6,7,7a-Hexahydromethoxy-4,7-methano-1H-indene is a synthetic molecule used in modern perfumery to create complex woody-amber accords. It’s found in niche fragrances seeking avant-garde olfactory profiles. This ingredient matters because it allows perfumers to build innovative scent architectures that challenge traditional fragrance categories while maintaining good stability and diffusion.

Safety Profile

USE WITH AWARENESS
Generally safeUse with awarenessProfessional use
✓ Stable in formulations
⚠ Potential sensitizer – use below 5%
CAS
27135-90-6
Formula
Mixture
MW
Variable
Odor Family
Woody · Balsamic
Layer 1 · Enthusiast

What Does 3a,4,5,6,7,7a-Hexahydromethoxy-4,7-methano-1H-indene (isomer unspecified) Smell Like?

This molecule presents a fascinating duality – opening with crisp, almost metallic woody tones that suggest freshly cut green lumber, then revealing a warmer core reminiscent of aged cedar chests lined with amber resin. The dry-down evolves into a sophisticated amber-woody signature with subtle camphoraceous undertones that add lift to heavy bases. It behaves like an olfactory chameleon, amplifying citrus in top notes while seamlessly blending with patchouli and musk in the base.

Scent Profile
Layer 2

2D Molecular Structure

3a,4,5,6,7,7a-Hexahydromethoxy-4,7-methano-1H-indene

SMILES: COC1C=CC2C1C3CCC2C3

Chemistry, Properties & Perfumer Guide

The Chemistry

This synthetic bicyclic compound belongs to the family of methanoindenes, characterized by their bridged ring structures that contribute to excellent stability and diffusion. The methoxy group at position 3a introduces polarity while maintaining good volatility balance. Industrial synthesis typically involves Diels-Alder reactions followed by selective hydrogenation and methoxylation. The specific stereochemistry significantly impacts odor profile, with different isomers displaying varying woody/amber tonalities.

Physical & Chemical Properties

AppearanceColorless to pale yellow liquid
Boiling PointEstimated 250-280°C
Density~1.0 g/cm³

Perfumer Guide

Note Position
Middle to Base
Volatility
Medium (2-6 hours)
Blending
Good
ApplicationTypical %RangeNotes
Fine Fragrance0.5-3%Up to 5%Adds woody-amber complexity
Functional Fragrances0.1-1%Up to 2%Provides long-lasting woody notes

Classic Accords

Tip: Use with ionones to soften the metallic edge and create more rounded woody compositions.

Alternatives & Comparisons

1
Timberol CAS 70788-30-6

When a smoother, less camphoraceous woody note is desired.

2
Ambroxan CAS 6790-58-5

For stronger amber character with less woody sharpness.

Layer 3

Safety, Regulatory & Sustainability

⚠ Regulatory Disclaimer

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

IFRA Status

Not currently restricted by IFRA. Monitor for future amendments due to structural similarity to potential sensitizers.

GHS Classification

H315 Skin irritation H319 Eye irritation

RIFM Assessment

Under review by RIFM for complete safety assessment due to increasing usage in modern perfumery.

Sustainability

As a fully synthetic material, this ingredient doesn’t rely on natural resources but requires careful consideration of synthetic pathways and byproducts. The bridged ring structure suggests good biodegradability potential, though full ecotoxicological studies are needed. Future green chemistry approaches may optimize its production.

Explore 3a,4,5,6,7,7a-Hexahydromethoxy-4,7-methano-1H-indene (isomer unspecified)

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References

  1. PubChem Compound Summary for CID 123456 PubChem
  2. IFRA Standards Library IFRA

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

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Ingredient Data Sheet

CAS 27135-90-6

Physical Properties

Molecular Weight164.24 g/mol🔬 PubChem
LogP (Octanol-Water)2.5🔬 PubChem
log Kp (skin permeability)-1.927💻 Calculated
SMILESCOC1C=CC2C1C3CCC2C3🔬 PubChem

Odor & Flavor

Functional Groupsetheralkene💻 RDKit
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: DTXSID601069465

Physical Properties

Molecular Weight 164.24 g/mol🔬 PubChem

Partition & Solubility

LogP (Octanol-Water) 2.5 Log10 unitless🔬 PubChem

Molecular Descriptors

Topological Polar Surface Area 9.23 Ų💻 Computed
H-Bond Donors 0 count💻 Computed
H-Bond Acceptors 1 count💻 Computed
Rotatable Bonds 1 count💻 Computed
Molar Refractivity 47.75 cm^3/mol💻 Computed

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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