Compounds · Aldehydes · Terpenoid pathway
Neral
Also known as cis-Citral · Citral b — an analysis may use any of these names
A softer lemon than geranial.
- CAS
- 106-26-3
- Formula
- C10H16O
- Molar mass
- 152.23
- Odour threshold
- 30 ppbin water
- Boiling point
- ≈ 227 °C at atmospheric pressure
For this compound the two axes sit close together. Volatility tells you whether it leaves a surface early or late; the threshold tells you how much of it the nose needs before it notices.
Must be declared on the label
This compound is on the list of allergens that must be declared individually on cosmetic labels in the European Union, as one of the 24 substances listed before Regulation 2023/1545. Name to use on the label: CITRAL — neral and geranial are declared together under one name, not separately.
The declaration threshold is 0.001% in leave-on products and 0.01% in rinse-off products. This is an EU requirement — see the regulations page for why it matters beyond the EU. This is not legal advice.
Where it comes from
Biosynthetic pathway: Terpenoid pathway — plants build them from identical five-carbon blocks.
About the threshold figure
Trade literature gives the detection threshold of neral — also called beta-citral — as between 30 and 460 parts per billion. We use the low end for consistency with how citral is recorded.
That range spans a factor of fifteen, while the range for mixed citral spans only a factor of four. Measurements for each isomer on its own are less certain than for the mixture.
Published thresholds differ by several orders of magnitude, because of differences in measuring method, sample purity and panel. The figure here is an order of magnitude for relative comparison, not a measurement. We give it only for compounds where the literature broadly agrees — 52 of the 106 compounds in the library. The rest are left blank rather than guessed.
Why it sits where it does
The (Z) isomer of citral — the methyl group and the carbonyl group lie on the same side of the double bond. Geranial is the (E) isomer, with them on opposite sides.
That geometric difference is enough to shift the boiling point by about two degrees, and neral, the lighter isomer, leaves first. On a smelling strip the soft sweet part arrives before the sharp part.
Citral is the common name for the mixture of these two isomers. In most natural sources geranial dominates and neral makes up the smaller share.
Where else you meet it
It accompanies geranial in every natural source of citral: lemongrass, lemon, litsea. The ratio between the two isomers varies with species and season, and that is one of the places where an analysis that separates the two lines says more than one that merges them.
Dictionary entries that mention this compound
About the boiling-point figure
Neral is the cis isomer of citral, geranial the trans isomer. They boil a few degrees apart — neral lower — and the human nose can tell them apart: neral is sweeter, geranial sharper. Why this detail matters