Hedione. Transparent jasmine.

Jasmine and a molecule

The smell of jasmine is built from many compounds. Some are sweet and waxy. There is indole, which gives jasmine its warm, heady, almost animal side. There is benzyl acetate, which adds a touch of fruit. And there is a smaller but important group: the jasmonates.

Methyl jasmonate is present in jasmine oil in small amounts. It also occurs in many other plants, where it works as a signal: plants use jasmonates to respond to wounding or insect bites. In other words, the molecule was a message between parts of a plant before it was a smell for people.

In the early 1960s Edouard Demole's team at Firmenich in Geneva was working on jasmine oil. In 1962 they reported isolating and identifying methyl jasmonate in jasmine, in Helvetica Chimica Acta.

Alongside this, Demole described and synthesised a relative: methyl dihydrojasmonate. Firmenich gave it the trade name Hedione.

A light version of jasmine

Smelled alone, Hedione is very soft. Some people notice little at first: a hint of jasmine, a hint of lemon peel, something like green tea. None of the depth, sweetness or heaviness of a real jasmine flower.

But inside another smell, Hedione does something strange. It does not stand out. It gives everything else more air. Flowers seem to open wider, citrus brightens, woods feel less dry. Perfumers reach for words like bright, clear, radiant, wide.

Synthetic Hedione is a mix of isomers. It was later found that the cis form carries most of the smell, and Hedione HC, rich in cis, is markedly stronger. The same molecule, arranged slightly differently in space, gives a very different strength.

Today Hedione is among the most used materials in perfume. Some formulas use it in very large proportions, as a base of air for everything else to stand in.

Eau Sauvage, 1966

In 1966 Edmond Roudnitska made Eau Sauvage for Christian Dior. Over lemon, bergamot, basil and rosemary he placed Hedione at a significant level. Eau Sauvage is usually cited as the first commercial perfume to use Hedione in a clear way.

The result was a citrus that did not vanish as citrus usually does. It stayed clear for longer, as if a layer of cool air lay beneath the more volatile parts.

Roudnitska wrote a good deal about his craft, and he valued reduction: few materials, each with a reason. Hedione suited that way of thinking. It added no new character to the story. It added pauses between the sentences.

From Eau Sauvage, Hedione went into thousands of other perfumes, for men and women, citrus and floral. It became almost invisible in modern perfume: everywhere, rarely named.

The smell of empty space

Most molecules in perfume are chosen because they resemble an object. Hedione is chosen because it gives objects room to breathe.

This suggests another way of understanding smell. We tend to think of smell as a property of things: flowers smell, wood smells. But smell actually lives in the air, between the object and the person. What we smell is that distance, not the flower itself.

Hedione is like moving attention from the flower to the space around it. Walking into a garden in the evening, we know the jasmine is there before we see it. The air tells us first. Hedione is the smell of that announcement.

Perhaps that is why it is so useful. A room full of things feels crowded. A room with space lets things be seen. Smell works the same way.