Meaningful Structural Descriptors from Charge Density

Abstract

This paper provides a short introduction to the basics of electron density investigations. The two predominant approaches for the modelling and various interpretations of electron density distributions are presented. Their potential translations into chemical concepts are explained. The focus of the article lies on the deduction of chemical properties from charge density studies in some selected main group compounds. The relationship between the obtained numerical data and commonly accepted simple chemical concepts unfortunately is not always straightforward, and often the chemist relies on heuristic connections rather than rigorously defined ones. This article tries to demonstrate how charge density analyses can shed light on aspects of chemical bonding and reactivity resulting from the determined bonding situation. Sometimes this helps to identify misconceptions and sets the scene for new unconventional synthetic approaches.

EL: the new aromaticity measure based on one-electron density function

“…), QTAIM has become one of the most powerful utilities of modern chemistry, forming a bridge between advanced theoretical, and experimental techniques. In particular the properties of the electron density function in the so-called bond critical point (BCP, the (3, -1) saddle point on electron density curvature being a minimum in the direction of the atomic interaction line and a maximum in two directions perpendicular to it) seem to be valuable information for chemists, since it was proven in many papers that the chemical bonding can be characterized and classified on the basis of electron density characteristics measured in BCPs [24,[39][40][41][42]. It was emphasized in many papers dealing with QTAIM applications that the presence of a bond path (BP, the line linking points of maximum electron density along the direction of the bond) linking a pair of atoms and the BCP corresponding to it fulfills the sufficient and necessary condition requiring that the atoms be bonded to one another [43,44].…”

Curly arrows meet electron density transfers in chemical reaction mechanisms: from electron localization function (ELF) analysis to valence-shell electron-pair repulsion (VSEPR) inspired interpretation

“…The density distribution r(r) of a molecule contains information not only on the atomic structure and electronic properties but also on the nature of the chemical bonds that lead ultimately to chemical reactivity. Recently, Stalke 47 has provided an introduction to the basics of r(r) investigations from a theoretical point of view, while Chopra 48 has emphasized the advances in understanding of chemical bonding from experimental and theoretical charge density analysis. The name of quantum chemical topology 49,50 has been introduced to embrace all topological investigations of three-dimensional scalar fields [51][52][53][54][55][56][57][58] to rationalize the chemical bond and further understanding of the chemical reactivity.…”

The generalized invariom database (GID)

“…Despite the success of the Hansen-Coppens and Stewarts varieties of rigid pseudoatom models in high-accuracy singlecrystal diffraction throughout the last decades (Coppens, 1997;Koritsá nszky & Coppens, 2001;Stalke, 2011), shortcomings in the model have become increasingly apparent. The analysis of Koritsá nszky et al (2012) (based on theoretical calculations) and the report by Fischer et al (2011) (based on experimental data to extremely high resolution) show that core polarization should also be taken into account for high-accuracy work.…”