Energy of Intramolecular Hydrogen Bonding in ortho-Hydroxybenzaldehydes, Phenones and Quinones. Transfer of Aromaticity from ipso-Benzene Ring to the Enol System(s).

Danuta Rusinska-Roszak

doi:10.3390/molecules22030481

Abstract

Intramolecular hydrogen bonding (HB) is one of the most studied noncovalent interactions of molecules. Many physical, spectral, and topological properties of compounds are under the influence of HB, and there are many parameters used to notice and to describe these changes. Hitherto, no general method of measurement of the energy of intramolecular hydrogen bond (EHB) has been put into effect. We propose the molecular tailoring approach (MTA) for EHB calculation, modified to apply it to Ar-O-H∙∙∙O=C systems. The method, based on quantum calculations, was checked earlier for hydroxycarbonyl-saturated compounds, and for structures with resonance-assisted hydrogen bonding (RAHB). For phenolic compounds, the accuracy, repeatability, and applicability of the method is now confirmed for nearly 140 structures. For each structure its aromaticity HOMA indices were calculated for the central (ipso) ring and for the quasiaromatic rings given by intramolecular HB. The comparison of calculated HB energies and values of estimated aromaticity indices allowed us to observe, in some substituted phenols and quinones, the phenomenon of transfer of aromaticity from the ipso-ring to the H-bonded ring via the effect of electron delocalization.

Highlights

Noncovalent interactions, such as hydrogen bonding, play an important role in supramolecular chemistry, drug-receptor interactions, drug design in chemical and biological processes, including molecular recognition, and the bioactivity of macromolecules [1,2,3]
The diagrams which show significant correlations between the listed parameters and the calculated energy of intramolecular hydrogen bond (EHB) are included at the end of this study
The last column contains data regarding the related strength of hydrogen bonding (HB) cited in the literature

Summary

Introduction

Noncovalent interactions, such as hydrogen bonding, play an important role in supramolecular chemistry, drug-receptor interactions, drug design in chemical and biological processes, including molecular recognition, and the bioactivity of macromolecules [1,2,3]. Deshmukh [21] used this method for systems containing multiple O-H···OH intramolecular hydrogen bonds Their energy was calculated by the fragmentation approach: the original optimized molecule was cut into three overlapping fragments, which are obtained by replacing the OH groups with the hydrogen atom, without optimization, to avoid conformational changes in it. ···O=C intramolecular hydrogen bond energy, fragmentation onsists of comparingFor theestimating energies of fragments of a molecule, in which the atomsa systematic of the donor, of each optimized molecule was carried out, using modified Deshmukh’s [21] methodology, which cceptor, and both groups forming the hydrogen bond are successively removed This allowed consists of comparing the energies of the fragments of a molecule, in which the atoms of the donor, voiding contact between both groups in any such built structures.

AIM

Results

Thetotransfer aromaticity in triformyloglucinol

H H OHOH OH OH

Summary and Discussion