Chemistry words for smell · SmellBook Learn (free) · smellbook.com/learn/science/chemistry-words
SMELL AND SCIENCE · COMPANION GUIDE
Chemistry words for smell.
Short definitions of the words used on SmellBook’s molecule pages and in the Smell and Science lessons, written for readers without a chemistry background. Where a word names a family of molecules, the guide lists the molecules in SmellBook’s evidence that ChEBI, an open chemical classification, places in that family.
These definitions are editorial: SmellBook editors wrote them to explain words used on molecule pages and in Smell and Science. They are not findings about any smell, and they do not say what any family of molecules smells like. Family membership comes from ChEBI, the open chemical classification maintained at EMBL-EBI.
Volatile compound
A compound that passes easily from a liquid or solid into the air. Only molecules that reach the nose through the air can be smelled, so smell research measures the volatile compounds a sample releases.
See also: Smells are mixtures
Odorant
A volatile compound that people can smell at the amount present. A sample can release many volatile compounds of which only some are odorants; studies that use human sniffers, such as gas chromatography–olfactometry, try to tell them apart.
See also: Finding the molecules that matter
Concentration and threshold
Concentration is how much of a compound is present in a given amount of air, liquid or food. An odour threshold is the lowest concentration at which people can detect a compound. A compound present in large amounts can matter little to a smell if its threshold is high, and a trace compound can matter a great deal if its threshold is very low. This is why SmellBook keeps “major component” apart from “key odorant”.
See also: Reading the limits of a finding · How a claim can name a molecule
Functional group
A small arrangement of atoms within a molecule, such as an oxygen double-bonded to a carbon, that chemists use to sort molecules into families. Most of the family words below are named after functional groups.
Aldehyde
A molecule with a –CHO group: a carbon carrying a double-bonded oxygen and a hydrogen, bonded to at most one other carbon, at the end of a chain or on a ring.
Aldehydes in SmellBook’s evidence (24): acetaldehyde, anisaldehyde, benzaldehyde, cinnamaldehyde, decanal, (E,Z)-2,6-nonadienal, (E)-2-hexenal, (E)-2-nonenal, formaldehyde, furfural, geranial, heptanal, hexanal, 2-methylbutanal, 3-methylbutanal, 2-methylpropanal, nonanal, octanal, 4-oxopentanal, pentanal, phenylacetaldehyde, vanillin, (Z)-3-hexenal, (Z)-6-nonenal ChEBI class: aldehyde (CHEBI:17478)
Ketone
A molecule with a carbon, bonded to two other carbons, that carries a double-bonded oxygen (C–CO–C), in a chain or a ring. Ketones differ from aldehydes in where that group sits.
Ketones in SmellBook’s evidence (14): acetoin, acetone, 2-acetyl-1-pyrroline, 2-acetylpyrrole, 2,3-butanedione, 2-butanone, dihydro-β-ionone, (E)-β-damascenone, 6-methyl-5-hepten-2-one, nootkatone, 4-oxopentanal, 2,3-pentanedione, thymoquinone, verbenone ChEBI class: ketone (CHEBI:17087)
Alcohol
A molecule with an oxygen–hydrogen group (–OH) attached to a carbon that is not part of a benzene ring. Ethanol, the alcohol in drinks, is one.
Alcohols in SmellBook’s evidence (18): acetoin, anisyl alcohol, benzyl alcohol, dihydromyrcenol, (E)-2-hexen-1-ol, ethanol, 2-ethylhexanol, geosmin, geraniol, 1-hexanol, isopropanol, linalool, methanol, nerol, 1-octen-3-ol, 2-phenylethanol, α-terpineol, (Z)-3-hexenol ChEBI class: alcohol (CHEBI:30879)
Carboxylic acid
A molecule with a carbon carrying both a double-bonded oxygen and an –OH group (–COOH). Acetic acid, in vinegar, is the best-known example.
Carboxylic acids in SmellBook’s evidence (6): acetic acid, butanoic acid, hexanoic acid, 3-methylbutanoic acid, pentanoic acid, propanoic acid ChEBI class: carboxylic acid (CHEBI:33575)
Ester
A molecule formed when a carboxylic acid joins with an alcohol, giving a –COO– link between two parts.
Esters in SmellBook’s evidence (21): anisyl acetate, benzyl acetate, benzyl tiglate, butyl acetate, butyrolactone, cis-3-hexenyl tiglate, δ-decalactone, γ-decalactone, dihydro-β-ionone, ethyl 2-methylpropanoate, ethyl acetate, ethyl butanoate, ethyl hexanoate, eugenyl acetate, hexyl hexanoate, isoamyl acetate, isopropyl dodecanoate, jasmine lactone, linalyl acetate, methyl benzoate, sotolon ChEBI class: carboxylic ester (CHEBI:33308)
Lactone
An ester whose –COO– link closes a ring, so the acid part and the alcohol part belong to the same molecule. The Greek letter in names such as γ-decalactone or δ-decalactone tells which carbon closes the ring, and so its size: γ gives a five-membered ring, δ a six-membered one.
Lactones in SmellBook’s evidence (5): butyrolactone, δ-decalactone, γ-decalactone, jasmine lactone, sotolon ChEBI class: lactone (CHEBI:25000)
Thiol and other sulfur compounds
A thiol has a sulfur–hydrogen group (–SH) where an alcohol has –OH. Other small sulfur compounds, such as sulfides (C–S–C), are grouped with thiols here because molecule pages often name them together.
Thiols in SmellBook’s evidence (3): ethanethiol, 3-mercapto-2-methylpentan-1-ol, methanethiol ChEBI class: thiol (CHEBI:29256)
Sulfides in SmellBook’s evidence (2): dimethyl sulfide, methional ChEBI class: organic sulfide (CHEBI:16385)
Terpene and terpenoid
Molecules built, mainly by plants, from five-carbon units. Terpenes contain only carbon and hydrogen; terpenoids also carry oxygen or other atoms.
Terpenoids in SmellBook’s evidence (20): borneol, carvacrol, chamazulene, 1,8-cineole, citronellol, dihydro-β-ionone, dihydromyrcenol, (E)-β-damascenone, geranial, geraniol, β-ionone, linalool, linalyl acetate, menthone, menthyl acetate, nerol, nootkatone, α-terpineol, thymol, verbenone ChEBI class: terpenoid (CHEBI:26873)
Phenol
A molecule with an –OH group attached directly to a benzene ring.
Phenols in SmellBook’s evidence (12): carvacrol, eugenol, eugenyl acetate, guaiacol, 4-methylguaiacol, 4-methylsyringol, p-cresol, phenol, syringol, thymol, vanillin, 4-vinylguaiacol ChEBI class: phenols (CHEBI:33853)
Hydrocarbon
A molecule made only of carbon and hydrogen. Terpenes in the strict sense are hydrocarbons; so are benzene, toluene and other compounds measured in air studies.
Hydrocarbons in SmellBook’s evidence (20): benzene, γ-cadinene, δ-3-carene, β-caryophyllene, ethylbenzene, α-farnesene, germacrene D, α-humulene, limonene, myrcene, naphthalene, octane, p-cymene, β-pinene, sabinene, styrene, α-terpinene, γ-terpinene, terpinolene, toluene ChEBI class: hydrocarbon (CHEBI:24632)
Isomers and enantiomers
Isomers are molecules with the same atoms arranged differently. Enantiomers are a special pair of isomers that are mirror images of each other, like left and right hands. A name that does not say which form was measured can be ambiguous. When the names a claim uses could mean more than one compound record, SmellBook records no identifier for that molecule rather than guess.
See also: α-pinene: names that resolve to more than one record
Families come from ChEBI’s own classification of each molecule’s ChEBI record, looked up on 2026-10-06 by an automated check. A molecule can belong to several families, or to none listed here. Molecules without a single agreed compound record, or without a ChEBI record, have no family in SmellBook. Belonging to a family says nothing about how a molecule smells.