trans,cis-2,6-Nonadienal is an organic compound that is classified as a doubly unsaturated derivative of nonanal.

The molecule consists of a α,β-unsaturated aldehyde with an isolated alkene group.

The compound has attracted attention as the essence of cucumbers,[1][2] but it is also found in bread crust[3] and freshly cut watermelon.

Isotopic labeling has indicated that nonadienal is formed from α-linolenic acid.

[4] Such reactions are typically catalyzed by hydroperoxide lyases.