Abstract: Reactions of the hydroxyl radical (OH) in the gas phase and at the gas-liquid interface initiate and propagate complex chemical schemes in combustion, planetary atmospheres, and the interstellar medium. In aqueous aerosols, the confinement of the reactants near the air-water interface leads to complex behavior of the particle reactive uptake with particle composition. In the gas phase, the branching ratio between the abstraction and addition mechanisms is highly dependent on the reactant’s structure and the gas temperature. The presentation will discuss the experimental and theoretical investigations of OH reactivity with a series of hydrocarbon reactants at the air-water interface and in the gas phase. Effects of resonance stabilization and surface-bulk partitioning will be highlighted.