Theoretical Exploration of Isomerization Pathways in H2SO4·HX (X = OH, Cl, Br) Complexes

Complexes formed by sulfuric acid (H2SO4) with HX (X = OH, Cl, Br) are critical in various chemical processes. In this work, we theoretically investigated the isomerization pathways of these complexes, analyzing their structures, energies, and reaction mechanisms. We identified eight, eight, and nine isomers for the H2SO4 + HX systems with X = OH, Cl, and Br, respectively, including mirror-symmetrized structures. The most stable complexes in each system are cyclic, stabilized by double hydrogen bonds forming six-membered rings. We discovered 7, 10, and 10 new transition states for the reaction involving X = OH, Cl, and Br, respectively. Isomer rearrangements primarily involve the hydrogen bond dynamics, hydrogen atom exchange, and cis–trans isomerization of H2SO4 due to wagging of its non-interacting O–H bond. Our findings underscore the dominance of hydrogen bonding in these intermolecular interactions and provide fresh insights into the nature and reactivity of these complexes.