Investigation of solvent effects on the aromaticity of hydroxybenzenes, considering magnetically induced current densities in adducts with explicit water molecules

Abstract

Evaluating the effects of a solvent on the properties of a solute molecule is important to understand its behavior in a solution of that solvent; this, in turn, is important because most reactions—including all the reactions in biological systems—occur in solution. In its most common definition, aromaticity is a property of molecules with delocalized electrons in a ring. It significantly influences their behavior and, therefore, it is important to evaluate the effects of a solvent on it. The most powerful magnetic criterion to estimate aromaticity considers magnetically induced current densities in the ring. The present work applies this approach to adducts of hydroxybenzenes with explicit water molecules. Hydroxybenzenes are selected as the simplest aromatic systems capable of forming solute–solvent hydrogen bonds with water molecules. Hydroxybenzenes without consecutive OH groups are selected to avoid the influence of intramolecular hydrogen bonds between OHs. Current densities are calculated focusing on the aromatic rings, and the effect of the solvent is highlighted by the density changes caused by the presence of the water molecules attached to the hydroxybenzene molecule. The results show that the strength of the ring current decreases as the number of OH groups in the molecule increases. The strength does not change greatly in the adducts with respect to the isolated molecules: the change extent and direction depend mostly on the arrangement of water molecules around the central molecule. The current density maps show that the water molecules may also be involved in the current flow.