The plant kingdom makes thousands of aromatic compounds, but a small number appear again and again. Know the ten below and you can read most commercial essential-oil analyses.
They are ordered by boiling point, that is, in the order you smell them.
The early group
Alpha-pinene, 155 °C. Pine, dry, sharp. Found in almost every conifer oil and many spice oils.
Limonene, 176 °C. Citrus peel, bright, slightly bitter at the edges. One of the most common molecules in the aromatics industry. It is not the fastest to oxidise, but because it is everywhere its trace of decay is the most familiar — the smell of old peel is oxidised limonene.
1,8-Cineole, 176 °C. Clean, cold in the nasal cavity. Found in eucalyptus, cajuput, galangal, bay leaf. One of the few compounds an untrained nose can name at once.
The middle group
Linalool, 198 °C. Floral, slightly sweet, flat. Found in more than two hundred species. On its own it is rather bland; its role is to form a background.
Camphor, 204 °C. Dry, sharp, woody. A high share of it in a sample labelled lavender is a sign worth questioning.
Terpinen-4-ol, 209 °C. Earthy, slightly medicinal. It is the main quality marker of tea tree oil.
Linalyl acetate, 220 °C. Sweet like pear, soft. Its ratio to linalool is the standard quality index for lavender.
The group that stays
Citral, 229 °C. Sharp lemon, with body. In fact a mixture of two isomers; an analysis that lists them separately says more than one that combines them.
Eugenol, 254 °C. Clove, warm, slightly numbing on the tongue. Found in clove, cassia leaf, holy basil — three unrelated plants.
Beta-caryophyllene, 264 °C. Wood, pepper, dry. The most common sesquiterpene in the plant kingdom, and almost nobody notices it until it is missing.
How to use this list
Don’t memorise it. Open the compound library and read one page at a time, one compound a day.
Each page gives you three things: how it smells, why it sits where it does on the volatility axis, and where you meet it outside essential oils. Together those three are enough to recognise it next time.
Once you are familiar with these ten, an analysis stops being a list of strange names and starts being a story with familiar characters.