trans-2-Methyl-2-butenal is an organic compound with the formula CH<sub>3</sub>CH=C(CH<sub>3</sub>)CHO. This colorless liquid is a building block in organic synthesis. It is an ñ,ò-unsaturated aldehyde related to the better-known crotonaldehyde. The European rabbit, Oryctolagus cuniculus, uses 2-methyl-2-butenal as a pheromone. The rabbit pheromone, trans-2-methyl-2-butenal, was reported to be involved in the communication between species, defined under the class of "interomone."