Understanding the intrinsic shape of bioactive molecules such as picaridin is key to elucidating their mode of action. In this work, we characterize the gas-phase conformational landscape of picaridin, a flexible chiral repellent with two stereocenters. Broadband rotational spectroscopy combined with quantum chemical calculations reveals a single dominant conformer per enantiomeric pair, both stabilized by internal O–H···O hydrogen bonds. These intramolecular interactions induce conformational locking, constraining the hydroxyethyl chain and favouring a compact geometry. Non-covalent interaction analysis further confirms that dispersion and hydrogen bonding play a central role in conformational selection under isolated conditions.
