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

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 π 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 π 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.

Malonaldehyde-like Systems: BeF2 Clusters—A Subtle Balance between Hydrogen Bonds, Beryllium Bonds, and Resonance

“…Therefore, the important conclusion is that the carbon chain of malonaldehyde is similarly modified in both cases; i.e., resonance should be very similar in the linear and the pseudocyclic structures. As we have already mentioned in the Introduction, we cannot forget that the cyclization of malonaldehyde has been shown to be a paradigmatic example of what is usually called a resonance-assisted hydrogen bond (RAHB) [66], although the nature of this phenomenon was a subject of debate [76][77][78][79][80][81][82]. In order to assess the possible role of electron delocalization phenomena, we have used the EDS formalism described in previous sections.…”

Correlation Effects in Trimeric Acylphloroglucinols

“…The length is shorter for the first IHBs, which are the strongest IHBs present. It can be recalled that the first IHB has an sp 2 O as acceptor and closes a 6-member ring containing two double bonds, which is known to stabilise an H-bond (resonance-assisted H-bond, [78][79][80][81]).…”

Molecular tailoring approach as tool for revealing resonance‐assisted hydrogen bond: Case study of Z‐pyrrolylenones with the NH⋯OС intramolecular hydrogen bond

“…Among hydrogen bonds, the so‐called resonance‐assisted hydrogen bonds (RAHBs) play a special role, as they are extremely strong and cause an appreciable change in the structure of the molecules involved in such an interaction. The RAHB concept, introduced by Gilli and co‐workers in 1989, 9 has been repeatedly questioned and revised, 10–17 but still remains generally accepted 18–32 . A classical RAHB concept assumes that a enhance in the strength of H‐bond takes place due to the resonance assistance causing the synergistic effect through an increase of the electron delocalization across the π‐conjugated fragment connecting the H‐bond donor and acceptor atoms 33,34 .…”

“…The RAHB concept, introduced by Gilli and co-workers in 1989, 9 has been repeatedly questioned and revised, [10][11][12][13][14][15][16][17] but still remains generally accepted. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] A classical RAHB concept assumes that a enhance in the strength of H-bond takes place due to the resonance assistance causing the synergistic effect through an increase of the electron delocalization across the π-conjugated fragment connecting the H-bond donor and acceptor atoms. 33,34 As a consequence, the Hbond donor gains a positive charge whereas the H-bond acceptor increases negative charge that, in turn, magnifies an electrostatic contribution to the total H-bond energy.…”