Interplay between intramolecular resonance-assisted hydrogen bonding and local aromaticity. II. 1,3-Dihydroxyaryl-2-aldehydes.

The interplay between aromaticity and hydrogen bonding in 1,3-dihydroxyaryl-2-aldehydes is investigated by means of quantum-chemical calculations. The position of the extra ring formed by substituents interacting through the hydrogen bond (HB) is found to influence both the strength of the HB and the local aromaticity of the polycyclic aromatic hydrocarbon (PAH) skeleton. The HBs are stronger and the entire system is energetically more stable when a kinked-like structure is generated by formation of the quasi-ring. Relatively greater loss of aromaticity of the ipso-ring can be observed for these kinked-like structures because of the larger participation of pi-electrons coming from the ipso-ring in the formation of the quasi-ring. We conclude that the quasi-ring partially adopts the role of a typical aromatic ring, the position of which has a meaningful influence on the aromaticity of the rest of the rings. This makes it possible to explain and modify the properties of 1,3-dihydroxyaryl-2-aldehydes by the planned substitution to the appropriate position of the given PAH.