Competition between In-Plane vs Above-Plane Configurations of Water with Aromatic Molecules: Non-Covalent Interactions in 1,4-Naphthoquinone-(H₂O)_1–3Complexes

Abstract

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–H···O and C–H···O 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–H···O, C–H···O, and lone pair···π-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–H···O binding with π and π-hole interactions. This study provides important insight into water interactions with aromatic systems and the challenges in their modeling.

Stepwise hydrations of anhydride tuned by hydrogen bonds: rotational study on maleic anhydride-(H2O)1–3

“…[9][10][11] When the aromatics contain heteroatoms or functional groups, water switches to the edgeways bind them with an in-plane configuration. [11][12][13][14] As the number of water molecules grows, complicated competition between in-plane and above-plane configurations of water molecules might emerge. 14 Besides, charge distributions and structural changes can be observed to be prominent dependent on stepwise complexation with H 2 O.…”

“…[11][12][13][14] As the number of water molecules grows, complicated competition between in-plane and above-plane configurations of water molecules might emerge. 14 Besides, charge distributions and structural changes can be observed to be prominent dependent on stepwise complexation with H 2 O. 15,16 Indeed, it has been shown that the bond lengths r(Na-Cl) increase with the growth of the number of water molecules.…”

The hydration of an oxy-polycyclic aromatic compound: the case of naphthaldehyde

“…19 When water is the solvent, it seems that the HB is preferentially formed with the electronegative heteroatom. This behaviour has been observed on a heterocyclic oxy-PAH (dibenzofuran), 20 a partially aromatic oxy-PAH (naphthoquinone), 21 a cyano-PAH 22 and a heterocyclic nitro-PAH. 23 Nonetheless, an interesting slightly different case deserves investigation: the hydration of a homocylic oxy-PAH which contains a functional group attached to fully aromatic rings.…”

“…Finally, the experimental results call for caution regarding the calculation methods. 21 In the case of β-naphthaldehyde where two monohydrates are predicted within less than 2 kJ mol −1 , namely trans -β-I and trans -β-II, experiments clearly point toward the latter being the most stable structure. This is in agreement with the prediction at the MP2/aug-cc-pVTZ level.…”

“…The dihydrates structures calculated to be the most stable for both isomers are I and II combinations, so that the positions I and II are preferred as for monohydrates and in agreement with the case of naphthoquinone. 21 The most favourable structures and their relative energies can be found in Tables S14 and S15 of the ESI †. Attempts to observe experimentally the most stable dihydrate for each isomer, namely cis -α-I-II and trans -β-I-II, were unsuccessful.…”