Aldehydes are organic compounds present in many natural materials (including roses), that also can be synthesized artificially. In 1921, while working on the creation of a perfume for Coco Chanel, the great nose Ernest Beaux was the first to use the synthetic component, to give sparkle to the iconic fragrance Chanel No. 5.
A Mini Science Lesson
Aldehydes are organic compounds which incorporate a carbonyl functional group (C=O). The carbon atom of this group has two remaining bonds that may be occupied by hydrogen or alkyl or aryl substituents. If at least one of these substituents is hydrogen, the compound is an aldehyde. (If neither is hydrogen, the compound is a ketone). Most fragrances today contain some type of aldehyde.
What They Smell Like
The most widely used aldehydes in perfumery are C7 (possessing a herbaceous green aroma), C8 (orange-like), C9 (smelling of roses), C10 (evoking orange rind), Citral, a complex 10-carbon aldehyde (fragrance of lemons), C11 (a clean, leafy green aroma), C12 (the odor of lilacs or violets), C13 (waxy, with grapefruit undertone), and C14 (evoking the scent of peach-skin). Chanel No. 5 (and later, No. 22) used a bouquet of aliphatic - or "fatty" - aldehydes (C10, C11, and C12) that together combine to produce a crisp citrus-and-floral note, with a pronounced soapy tone.
Perfumes using aldehydes may be floral, fruity or citrus in nature. Popular aldehydic fragrances include Chanel No. 5 and 22, Lanvin Arpege, Jean Patou Joy, Chloe, Yves Saint Laurent Rive Gauche, Elizabeth Taylor White Diamonds, Givenchy Ysatis, Dior Miss Dior, Estee Lauder Knowing, Guerlain Vol de Nuit, Avon Rare Gold, Joop! Femme, Tommy Hilfiger True Star, Givenchy L'Interdit, Agent Provocateur Maîtresse, Dolce & Gabbana Classique, and Lagerfeld Femme.