Get To Know Your Aldehydes

Do you know your aldehydes from your ketones?

Perfume and fragrances can seem magical at times, able to evoke long buried memories with just a whiff, but there is some pretty serious science behind their function!  There are two principle types of organic compounds that produce the scents that we are familiar with - ketones and aldehydes.  Ketones are heavier and generally pleasant smelling, but today we will be focusing on aldehydes - generally the better known of the two types in the world of perfumery.

An aldehyde is an organic compound that contains a carbonyl group (a carbon atom which is double bonded to an oxygen atom).  Aldehydes can vary greatly in complexity and structure - the lower weight molecules actually tend to smell quite unpleasant.  Fortunately, the versions that have chains of carbon molecules attached to them have rather nice aromas.  

While most commonly thought of as chemicals formulated in laboratory conditions, aldehydes do occur naturally, in escences of orange rind, rose oil, pine, citronella, and cinnamon bark as common examples.

Aldehydes were first formulated by Carl Whilhelm Scheele in 1774, but it was not until 1834 that Justus von Liebig was able to fully describe the compounds and their preparation from ethanol and dubbed them "aldehydes".

Fougere Royale  by Paul Parquet for Houbigant (the first modern perfume to use aldehydes in its blending).

The forms most commonly used in perfumes are the C group, which contain long chains of carbon atoms bonded to the main carbonyl group.  

Heptanal (C7) herbal green, occurs naturally in Clary Sage

Octanal (C8) orange-like

Nonanal (C9) rose-like

Decanal (C10) orange rind/zest - Citral ( variant) smells of lemons

Undecanal (C11) "clean" - occurs naturally in coriander leaf

Lauryl Aldehyde (c12) reminiscent of lilacs or violets

C13 - waxy grapefruit

This group of compounds is responsible for many of the most common commercial fragrances, including non-perfume products such as deodorants, detergents and other scented household goods.

Chanel No. 5 - the "gold standard" of synthetic aldehyde fragrances.

The grouping of C10 through C12 in the formulation of Chanel No. 5 proved popular enough that it became the standard bouquet for aldehydic perfumes for quite some time and remains the scent that most wearers associate with the concept of "perfume".  However, aldehydes have a large range of scents and have been used in well known blends across the spectrum.

While perfumery has moved towards natural fragrances in recent years, aldehydes remain a useful tool in fragrance blending, by enabling the development of notes that are not feasible to make using only naturally occurring scent compounds.  One of the enduring myths about aldehydes is that they are only useful for imbuing the classic effervescent "perfume" note found in Chanel No. 5, but in fact they are useful for creating an entire range of notes from earthy and green to bright and citrusy, even floral notes.