Trans-2-Hexenal

trans-2-Hexenal is an organic unsaturated aldehyde with a six-carbon chain. This clear, pale yellow liquid has a green, leafy, herbal fruit smell. It occurs naturally in a wide variety of plants, fruits, vegetables, and spices, and appears to be an important mediating and signalling chemical in plant-fungus and plant-insect interactions, such as the symbiosis between acacia ants and Acacias.^[1][2]

trans-2-Hexenal

Names
Preferred IUPAC name (2E)-hex-2-enal
Other names (trans)-2-Hexenal (2(E))-hexenal 6728-26-3 (E)-Hex-2-enal 3-propylacrolein β-propylacrolein
Identifiers
CAS Number	6728-26-3
3D model (JSmol)	Interactive image
ChEBI	CHEBI:28913
ChEMBL	ChEMBL2228570
ChemSpider	4444608
ECHA InfoCard	100.027.072
EC Number	229-778-1
KEGG	C08497
PubChem CID	5281168
UNII	69JX3AIR1I
CompTox Dashboard (EPA)	DTXSID1041425
InChI InChI=1S/C6H10O/c1-2-3-4-5-6-7/h4-6H,2-3H2,1H3/b5-4+ Key: MBDOYVRWFFCFHM-SNAWJCMRSA-N
SMILES CCC/C=C/C=O
Properties
Chemical formula	C6H10O
Molar mass	98.14 g/mol
Density	0.841-0.848 g/cm3
Boiling point	47.00°C @ 17.00 mmHg
Vapor pressure	6.6 mmHg
Hazards
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H226, H302, H311, H317, H319, H411
Precautionary statements	P210, P233, P240, P241, P242, P243, P261, P262, P264, P264+P265, P270, P272, P273, P280, P301+P317, P302+P352, P303+P361+P353, P305+P351+P338, P316, P321, P330, P333+P317, P337+P317, P361+P364, P362+P364, P370+P378, P391, P403+P235, P405, P501
Related compounds
Related alkenals	(cis)-3-hexenal
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Occurrence

This aldehyde is a commonly produced volatile organic compound (VOC) among the flowering plants. It is among the VOCs known as green leaf volatiles, as they are released following damage to the leaf, whether by crushing, herbivory, or bacterial or fungal infection. It is also found in other parts of the plant. For example, it was found to constitute 34% of the total VOCs from fresh strawberry fruits and 28% of VOCs from fresh tomato fruits.^[3]

trans-2-hexenal appears to be an airborne signalling chemical that can upregulate plant defenses, from leaf to leaf on the same plant as well as between neighboring plants.^[4] It has been shown to inhibit the growth of fungal pathogens.^[5]

It is also implicated in the mutualistic relationship between Acacia and related trees and their ant partners. The bullhorn acacia tree, Vachellia cornigera, grows inflated hollow spines at the base of its leaves that serve as nesting places for its symbiotic partner, the acacia ant, Pseudomyrmex ferruginea. The tree produces sugary nectar and fat- and protein-rich nutrient packets at the tips of its leaflets to serve as food for the ants. In return, the ants react aggressively towards any pest or herbivore which damages the Acacia leaves. It is the release of trans-2-hexenal from the damaged leaf that the ants sense and react to.^[6][1][7]

Uses

This aldehyde is approved for use as a food additive and is used, highly diluted, in perfumery.^[8] It is said to lend a green apple, leafy, herbal, spicy banana note to a fragrance.^[9]

It may also find use as an antifungal agent, including as a post-harvest fruit preservative.^[10][11]

See also

• Myrmecophyte, a plant that lives in a mutualistic association with ants
• Synomone, a signalling chemical which benefits both parties in a symbiotic relationship
• Plant defense against herbivory
• Plant communication
• cis-3-Hexenal, a similar aldehyde which also mediates plant-insect interactions