(1R,2S)-rel-2-(3,4-Difluorophenyl)cyclopropanamine hydrochloride is a chiral cyclopropylamine derivative. It features a cyclopropane ring substituted with an amine group and a 3,4-difluorophenyl group, and is supplied as its hydrochloride salt. The "rel" designation indicates the relative stereochemistry of the two chiral centers. This compound is a key chiral building block in pharmaceutical research and development. Its primary application is as a crucial intermediate in the synthesis of novel bioactive molecules, particularly in the discovery of antiviral and central nervous system (CNS) active drugs. The rigid cyclopropane scaffold and the chiral amine functionality are valuable structural motifs for modulating the potency, selectivity, and metabolic stability of drug candidates. As a high-value synthetic intermediate, it is typically used in advanced stages of medicinal chemistry campaigns to construct complex target molecules. Its handling requires standard precautions for amine hydrochlorides and should be stored in a cool, dry place.