The smell of specific Chemical Groups
Introduction to Olfactory Chemistry
Each chemical class found in perfumery exhibits a distinctive and recognizable olfactory profile. These scent patterns arise from the functional groups present in the molecules, influencing both volatility and receptor interaction.
This article outlines the main classes of aromatic compounds and their typical smells, with examples from perfumery and everyday olfaction.
Volatility and Molecular Weight in Smell Perception
Odor perception is strongest for volatile, low molecular weight compounds, as these molecules readily evaporateand interact with olfactory receptors. As molecular weight increases, volatility—and often olfactory intensity—decreases.
The Smell of Specific Chemical Groups
Alcohols
Alcohols typically exhibit fresh and pleasant odors, especially in the lower molecular weight range. Over time, however, these scents can evolve or diminish in appeal.
Cis-3-Hexenol: Known as “leaf alcohol”, this molecule has a green, fresh-cut grass odor initially, later developing into a fuel-like, herbaceous nuance.
Phenols
Phenols generally possess sharp, often unpleasant odors, with some notable exceptions.
Most phenols are described as acrid or medicinal.
Anethole and estragole, both methylated phenylpropenes, are exceptions—offering sweet, licorice-like aromas.
Diphenyl oxide: Derived from phenol, it imparts powdery floral notes, especially useful in rose accords.
Phenoxyethanol and its esters, such as phenoxyethyl isobutyrate, add soft, mildly fruity facets to formulations.
Aldehydes and Ketones
These compounds are often highly volatile, resulting in potent, sometimes overwhelming smells.
Formaldehyde and acetaldehyde: Sharp, irritating, and pungent.
Valeraldehyde and butyraldehyde: Strong, often nauseating.
Ketones can vary widely, with some contributing musk-like or fruity nuances.
Due to the absence of hydrogen bonding, aldehydes and ketones evaporate easily, enhancing their olfactory impact.
Carboxylic Acids
Carboxylic acids tend to emit acrid, sour odors, especially in the lower molecular weight range.
Acetic acid: Smells like vinegar.
Butyric acid: Has a rancid, vomit-like smell, used only in trace amounts or chemically modified in perfumery.
Esters
Esters are among the most pleasant-smelling chemical groups, frequently evoking fruit or flower notes.
Linalyl acetate: Floral, lavender-like, fresh.
Ethyl acetate: Fruity with vinegary edges, solvent-like.
Ethyl propionate: Smells like chewing gum.
Amyl acetate: Classic banana aroma.
Ethyl butyrate: Intense smell of overripe strawberries.
These compounds are foundational in fruity and gourmand accords.
Amines
Amines, particularly at low molecular weight, are known for their pungent, ammonia-like odors.
As complexity increases (e.g., diamines or isonitriles), the smell worsens—commonly described as rotting fish or decaying organic matter.
Used cautiously, often masked or modified through derivatization or encapsulation.
Sources
Fulvio Ciccolo, "La grammatica dei profumi", 2020
Scentspiracy Research
Peer-reviewed articles on structure-odor relationships in perfumery chemistry