Competition between In-Plane vs Above-Plane Configurations of Water with Aromatic Molecules: Non-Covalent Interactions in 1,4-Naphthoquinone-(H2O)1-3 Complexes

Non-covalent interactions between aromatic molecules and water are fundamental in many chemical and biological processes, and their accurate description is essential to understand molecular relative configurations. Here we present the rotational spectroscopy study of the water complexes of the polycyclic aromatic hydrocarbon 1,4-naphthoquinone (1,4-NQ). In 1,4-NQ-(H2O)1,2, water molecules bind through O-HmiddotmiddotmiddotO and C-HmiddotmiddotmiddotO hydrogen bonds and are located on the plane of 1,4-NQ. For 1,4-NQ-(H2O)3, in -plane and above-plane water configurations are observed exhibiting O-HmiddotmiddotmiddotO, C-HmiddotmiddotmiddotO, and lone pairmiddotmiddotmiddot pi-hole interactions. The observation of different water arrangements for 1,4-NQ-(H2O)3 allows benchmarking theoretical methods and shows that they have great difficulty in predicting energy orderings due to the strong competition of C-HmiddotmiddotmiddotO binding with pi and pi- hole interactions. This study provides important insight into water interactions with aromatic systems and the challenges in their modeling.