Comparison of Resonance Assisted and Charge Assisted Effects in Strengthening of Hydrogen Bonds in Dipyrrins

Abstract

This paper deals with the study of two types of hydrogen bonding: a quasi-aromatic hydrogen bonding in dipyrromethene and the ionic one in dipyrromethane. The study focuses on two phenomena-the proton transfer process and tautomeric equilibrium. Metric parameters and spectroscopic assignments have been calculated; this allowed a further comparison of spectral features calculated with four methods (Car-Parrinello molecular dynamics (CPMD), ab initio, density functional theory (DFT), and numerical calculation of anharmonic vibrational levels via a solution of the corresponding 1D Schrödinger equation). A significant dynamics of the bridged proton and bent vibration of pyrrole fragments in dipyrromethane have been exposed by the CPMD calculations. The prevailing of the ionic effect over the π-electronic coupling in the strengthening of the hydrogen bonding has been shown on the basis of the calculated structural, electron-topological, and spectral data as well as potential energy surface (PES). The analysis of the aromaticity and electronic state of pyrrole and chelate moieties depending on the tautomeric equilibrium by the quantum theory of atoms in molecules (QTAIM) method was conducted. The principle divergence in the behavior of aromaticity of the chelate chains in the analyzed compounds was demonstrated.

Inter- vs. Intramolecular Hydrogen Bond Patterns and Proton Dynamics in Nitrophthalic Acid Associates

“…Molecular dynamics (MD) schemes, which reproduce time evolution of the studied systems, are useful in the investigations of multi-dimensional and complex phenomena [ 80 , 81 , 82 ]. In the studied case of phthalic acid derivatives, it was necessary to use the Car–Parrinello MD scheme (CPMD), which is based on the DFT framework and is able to reproduce H-bond properties [ 83 , 84 , 85 , 86 , 87 , 88 ]. This section describes how these CPMD simulations illustrate the impact of H-bond strength on the molecular metric parameters.…”

Intramolecular Hydrogen Bonds in Selected Aromatic Compounds: Recent Developments

“…These results, elucidated in publication [14], made it possible to find a tool for the analysis of RAHB, namely the dependence of the energy of hydrogen bonding on the HOMA aromaticity index of the chelate chain (∆EHB = f(HOMA(ch)), Figure 6). The main objective of paper [44] was to study the compounds with resonance assisted hydrogen bonding (RAHB in dipyrromethene-III) and charge assisted hydrogen bonding (CAHB in dipyrromethane anion-IV). The dipyrrines studies performed proved that the CAHB is stronger than the RAHB in terms of the global energy minimum.…”

“…The reason for this is that the strengthening of hydrogen bonding via the charge (CAHB) is more powerful than the strengthening by resonance (RAHB). However, it is of importance that the increase of π-electronic coupling (the growth of the HOMA(ch) index) causes the strengthening of hydrogen bonding in dipyrromethene if compared The main objective of paper [44] was to study the compounds with resonance assisted hydrogen bonding (RAHB in dipyrromethene-III) and charge assisted hydrogen bonding (CAHB in dipyrromethane anion-IV). The dipyrrines studies performed proved that the CAHB is stronger than the RAHB in terms of the global energy minimum.…”