Hydrogen-bond-assisted conformational selection of picaridin in the gas phase†

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.