On the Relationship between Hydrogen Bond Strength and the Formation Energy in Resonance-Assisted Hydrogen Bonds.

José Manuel Guevara-Vela,Miguel Gallegos,Tomás Rocha-Rinza,Ángel Martín Pendás,Mónica A Valentín-Rodríguez,Aurora Costales

doi:10.3390/molecules26144196

Abstract

Resonance-assisted hydrogen bonds (RAHB) are intramolecular contacts that are characterised by being particularly energetic. This fact is often attributed to the delocalisation of electrons in the system. In the present article, we assess this thesis via the examination of the effect of electron-withdrawing and electron-donating groups, namely −F, −Cl, −Br, −CF3, −N(CH3)2, −OCH3, −NHCOCH3 on the strength of the RAHB in malondialdehyde by using the Quantum Theory of Atoms in Molecules (QTAIM) and the Interacting Quantum Atoms (IQA) analyses. We show that the influence of the investigated substituents on the strength of the investigated RAHBs depends largely on its position within the skeleton. We also examine the relationship between the formation energy of the RAHB and the hydrogen bond interaction energy as defined by the IQA method of wave function analysis. We demonstrate that these substituents can have different effects on the formation and interaction energies, casting doubts regarding the use of different parameters as indicators of the RAHB formation energies. Finally, we also demonstrate how the energy density can offer an estimation of the IQA interaction energy, and therefore of the HB strength, at a reduced computational cost for these important interactions. We expected that the results reported herein will provide a valuable understanding in the assessment of the energetics of RAHB and other intramolecular interactions.

Highlights

The structure and observable properties of condensed phases depend greatly on noncovalent interactions (NCI)
We examine the relationship between the formation energy of the Resonance-assisted hydrogen bonds (RAHB) and the hydrogen bond interaction energy as defined by the Interacting Quantum Atoms (IQA) method of wave function analysis
The IQA methodology partitions the energy of an electronic system into intra- and interatomic terms, a condition that allows the study of individual interactions within a molecule

Summary

Introduction

The structure and observable properties of condensed phases depend greatly on noncovalent interactions (NCI). We carried out electronic structure calculations as well as QTAIM and IQA analyses for a series of malondialdehydes substituted at different positions of the conjugated π system with an electron-withdrawing (EWG: −F, −Cl, −Br and −CF3) or an electron-donating (EDG: −N(CH3)2, −OCH3 and −NCOCH3) group [41] These calculations enabled us (i) to study the effect of substituents in the strength of the RAHB depending on its relative position and (ii) to compare the values of the IQA interaction energies and other parameters from different EDA analyses on one hand, and the corresponding RAHB formation energies on the other. We expect the present investigation to yield novel insights about the different methods to compute the strength of RAHB and other relevant non-covalent intramolecular interactions

Theoretical Framework

Models to Estimate the Energies of Intramolecular Hydrogen Bonds

Computational Details

Results

Influence of Substitution on RAHB Energetics

Conclusions