Citronellal

Say itsit-ruh-NEL-al

Powerful fresh lemon-citronella, green and waxy, slightly rosy.

What it is: A molecule made in a lab.
Where it comes from: from citronella oil or by hydrogenating citral
When you smell it: Top notes: the first minutes.
What perfumers do with it: Adds diffusive lemony-green freshness in functional perfumery; precursor to hydroxycitronellal and menthol.
Worth knowing: Takasago's menthol route, built on Ryoji Noyori's Nobel-winning catalyst, passes through pure (R)-citronellal.
Rules: Limited. Skin sensitizer; IFRA dose limits by product type
Also called: 3,7-Dimethyloct-6-enal

Not on the label of any of the 232 perfumes read so far.

Sources