Toward deformation densities for intramolecular interactions without radical reference states using the fragment, atom, localized, delocalized, and interatomic (FALDI) charge density decomposition scheme

It is shown herein that intuitive and text‐book steric‐clash based interpretation of the higher energy “in‐in” xylene isomer (as arising solely from the repulsive CH⋅⋅⋅HC contact) with respect to the corresponding global‐minimum “out‐out” configuration (where the clashing C−H bonds are tilted out) is misleading. It is demonstrated that the two hydrogen atoms engaged in the CH⋅⋅⋅HC contact in “in‐in” are involved in attractive interaction so they cannot explain the lower stability of this isomer. We have proven, based on the arsenal of modern bonding descriptors (EDDB, HOMA, NICS, FALDI, ETS‐NOCV, DAFH, FAMSEC, IQA), that in order to understand the relative stability of “in‐in” versus “out‐out” xylenes isomers one must consider the changes in the electronic structure encompassing the entire molecules as arising from the cooperative action of hyperconjugation, aromaticity and unintuitive London dispersion plus charge delocalization based intra‐molecular CH⋅⋅⋅HC interactions.

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“…Conformational deformation density (a change from a reference conformer, ref , to a final conformer, fin ) is calculated as:

true Δ_{c} ρ ((), r) = \sum_{normalA}^{M} Δ_{c} ℒ_{A} ((), r) + \sum_{normalA}^{M - 1} \sum_{normalB > A}^{M} Δ_{c} 𝒟_{normalA, normalB} ((), r)

…”

Section: Methodsmentioning

confidence: 99%

“…where

^{r e f} 𝒟_{A, B}^{ℛ} (boldr)

refers to the weighted contribution of

^{r e f} 𝒟_{A, B}

at both A A r and A B r . More details are in the ESI file, part 4.…”

Section: Methodsmentioning

confidence: 99%

Origin of Hydrocarbons Stability from a Computational Perspective: A Case Study of Ortho‐Xylene Isomers

et al. 2020

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“…We recently introduced the FALDI ED decomposition scheme . FALDI uses concepts from the domain averaged Fermi hole (DAFH) approach to calculate pseudo‐second‐order contributions arising from electrons within QTAIM‐defined atomic basins.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…This approach is flawed, as it only measures the local , relative electron concentration rather than the absolute, and resultantly shows a large dependence on the local environment. Our own fragment, atom, localized, delocalized, and interatomic (FALDI) density decomposition scheme provides absolute measures of electron concentration for 1‐ and 2‐center ED distributions. Hence, FALDI provides a much more trustworthy measure with regards to a concentration (and its origin) of ED within an internuclear region.…”

Section: Introductionmentioning

confidence: 99%

“…In principle, this approach can be taken with a large number of established ED decompositions. However, we have chosen our recently developed FALDI density decomposition scheme, as FALDI is (i) inherently linked to QTAIM atomic basins and populations, and (ii) FALDI can provide visualization and quantify electron exchange‐correlation channels in real 3D space.…”

Section: Introductionmentioning

confidence: 99%

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FALDI‐based criterion for and the origin of an electron density bridge with an associated (3,–1) critical point on Bader's molecular graph

2018

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The total electron density (ED) along the λ 2 -eigenvector is decomposed into contributions which either facilitate or hinder the presence of an electron density bridge (DB, often called an atomic interaction line or a bond path). Our FALDI-based approach explains a DB presence as a result of a dominating rate of change of facilitating factors relative to the rate of change of hindering factors; a novel and universal criterion for a DB presence is, thus, proposed. Importantly, facilitating factors show, in absolute terms, a concentration of ED in the internuclear region as commonly observed for most chemical bonds, whereas hindering factors show a depletion of ED in the internuclear region. We test our approach on four intramolecular interactions, namely (i) an attractive classical H-bond, (ii) a repulsive OÁÁÁO interaction, (iii) an attractive ClÁÁÁCl interaction, and (iv) an attractive CHÁÁÁHC interaction. (Dis) appearance of a DB is (i) shown to be due to a "small" change in molecular environment and (ii) qualitatively and quantitatively linked with specific atoms and atom-pairs. The protocol described is equally applicable (a) to any internuclear region, (b) regardless of what kind of interaction (attractive/repulsive) atoms are involved in, (c) at any level of theory used to compute the molecular structure and corresponding wavefunction, and (d) equilibrium or nonequilibrium structures. Finally, we argue for a paradigm shift in the description of chemical interactions, from the ED perspective, in favor of a multicenter rather than diatomic approach in interpreting ED distributions in internuclear regions.

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FALDI‐based decomposition of an atomic interaction line leads to 3D representation of the multicenter nature of interactions

2018

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Atomic interaction lines (AILs) and the QTAIM's molecular graphs provide a predominantly two-center viewpoint of interatomic interactions. While such a bicentric interpretation is sufficient for most covalent bonds, it fails to adequately describe both formal multicenter bonds as well as many non-covalent interactions with some multicenter character. We present an extension to our Fragment, Atomic, Localized, Delocalized and Interatomic (FALDI) electron density (ED) decomposition scheme, with which we can measure how any atom-pair's delocalized density concentrates, depletes or reduces the electron density in the vicinity of a bond critical point. We apply our method on five classical bonds/interactions, ranging from formal either two- or three-center bonds, a non-covalent interaction (an intramolecular hydrogen bond) to organometallic bonds with partial multicenter character. By use of 3D representation of specific atom-pairs contributions to the delocalized density we (i) fully recover previous notion of multicenter bonding in diborane and predominant bicentric character of a single covalent CC bond, (ii) reveal a multicenter character of an intramolecular H-bond and (iii) illustrate, relative to a Schrock carbene, a larger degree of multicenter MC interaction in a Fischer carbene (due to a presence of a heteroatom), whilst revealing the holistic nature of AILs from multicenter ED decomposition. © 2018 Wiley Periodicals, Inc.

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Toward deformation densities for intramolecular interactions without radical reference states using the fragment, atom, localized, delocalized, and interatomic (FALDI) charge density decomposition scheme

Cited by 13 publications

References 59 publications

Origin of Hydrocarbons Stability from a Computational Perspective: A Case Study of Ortho‐Xylene Isomers

Origin of Hydrocarbons Stability from a Computational Perspective: A Case Study of Ortho‐Xylene Isomers

FALDI‐based criterion for and the origin of an electron density bridge with an associated (3,–1) critical point on Bader's molecular graph

FALDI‐based decomposition of an atomic interaction line leads to 3D representation of the multicenter nature of interactions

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