Compiled from the Note Identification Project thread:
Helional Ė Milder than I expected. Haylike, but not actually harsh. Real hay absolute takes you on a much wilder ride. This is simplified, like a bit of grass dried in the sun. Hay absolute is prettier, but it asserts itselft like crazy in a fragrance. I can see the use for a synthetic.
Helional: getting very faint whiffs of wet floral alternating with nail polish remover.
Helional, 2% dilution in carrier oil: the same effect as Calone, but sweeter and a tad more fruity. Also longer lasting.
Helional is described by the manufacturer IFF as:
It also goes by a number of other names including ocean propanal, tropional, florial and floramelon.Green, floral (cyclemen) with top notes of ozone and new mown hay
The TGSC description is:
[note that these descriptors are presented in order of prominence in the odour]watery, fresh, green, ozone, cyclamen, hay
I find it a deceptive material that is rather underwhelming on first sniff but has a distinctive smooth, fresh, floralising effect in a fragrance blend. It is restricted by IFRA to 5.3% of the final product when used in alcoholic fragrances, but that still allows for quite high usage and is one of the few green notes that can be used relatively freely without overwhelming and dominating everything else (compare with Cucumber Aldehyde, Galbanum, Violet Leaf Absolute or Stemone for example).
In pure form it needs careful storage to avoid deterioration - on an industrial scale it is stored under nitrogen.