Hexenal (and ‘Green Grass’ Smell)

(Z)-3-Hexenal is the key aroma substance emitted when grass is cut and other types of vegetation are damaged. It has a very low odor threshold of 0.25 parts per billion. These volatile compounds, mainly C₆-aldehydes and C₆-alcohols, including (Z)-3-hexenal, (E)-2-hexenal and (Z)-3-hexenol, make up the ‘green odor’ from cut leaves, and are collectively known as GLVs, ‘Green Leaf Volatiles’. (E)-2-Hexenal is one of a number of aldehydes found in coriander, widely used in cooking. (E)-2-hexenal and hexyl acetate are chief among molecules responsible for the freshness of apple juice flavor, and thus hexenals can be used as additives to make flavors have a greener ‘edge’ to them. Bedbugs use a mixture of (E)-2-hexenal and (E)-2-octanal to deter unwanted advances during mating! Stink bugs, important agricultural predators, use (E)-2-hexenal as an attractant and pheromone, and it is thus a potential weapon to protect crops.