The Origin of the Non-Additivity in Resonance-Assisted Hydrogen Bond Systems

Abstract

The concept of resonance-assisted hydrogen bond (RAHB) has been widely accepted, and its impact on structures and energetics can be best studied computationally using the block-localized wave function (BLW) method, which is a variant of ab initio valence bond (VB) theory and able to derive strictly electron-localized structures self-consistently. In this work, we use the BLW method to examine a few molecules that result from the merging of two malonaldehyde molecules. As each of these molecules contains two hydrogen bonds, these intramolecular hydrogen bonds may be cooperative or anticooperative, depended on their relative orientations, and compared with the hydrogen bond in malonaldehyde. Apart from quantitatively confirming the concept of RAHB, the comparison of the computations with and without π resonance shows that both σ-framework and π-resonance contribute to the nonadditivity in these RAHB systems with multiple hydrogen bonds.

Nature of Intramolecular Resonance Assisted Hydrogen Bonding in Malonaldehyde and Its Saturated Analogue

“…This is in line with the recent work by Jiang and co-workers. 25 , 26 The intramolecular hydrogen bond in MA is further enhanced by σ orbital interactions. There is, however, no resonance assistance in the sense of a synergistic interplay between the σ and π electronic systems; the σ and π interactions enhance the intramolecular hydrogen bond in MA independently from each other.…”

Multiple Reversible Dynamics of Pyrimidine Based Acylhydrazones

“…That is, the distance of the hydrogen bond is shortened and subsequently, the strength of the hydrogen bond increases. [34,35] Likewise, as the thermal energy of the system decreases, the single bond rotation (carbon -2 from the pyrimidine-imine carbon) becomes slower favoring the interaction of the -NH proton with the pyrimidine nitrogen′s free electron pair. In this regard, the motivation to use a pyrimidine fragment was, at first, to be able to slow down the single bond rotation (the bond connecting the pyrimidine with the imine moieties) by an intramolecular hydrogen bond that could serve as a thermal brake observable by VT 1 H NMR through coalescence and splitting of signals as the temperature was decreased.…”

Magnetic descriptors of hydrogen bonds in malonaldehyde and its derivatives

“…As a consequence the donor group increases its positive charge and so it produce a large electrostatic interaction, which in turn shorten the distance of the HB and this increases its strength. [43][44][45][46] The electronic origin of the RAHB is under continuous debate. Celia Fonseca and collaborators studied the redistribution of the σ and π-electronic framework associated with the HB formation in MA and its saturated derivatives.…”