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Advances in the Theory of Chemical Bonding

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Physical Chemistry".

Deadline for manuscript submissions: closed (31 July 2021) | Viewed by 22232

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Prof. Dr. Ángel Martín Pendás

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Departamento de Química Física y Analítica, Julián Clavería, 6, Facultad de Química, Universidad de Oviedo, Oviedo, Spain
Interests: chemical bonding theory; quantum chemical topology; simulation of materials; matter at high pressure; methods in theoretical chemistry

Special Issue Information

Dear Colleagues,

It has been over a hundred years now since the seminal paper by G. N. Lewis was published in 1916, and many of the fundamental questions regarding the nature chemical bonds are still a subject of debate. We have recently witnessed, for instance, how purportedly well-established concepts like the steric nature of simple rotation barriers or the multiple-bonded character of naïve diatomics have been questioned with new interpretive tools. A literature survey also shows that as new fields become of interest, e.g., noncovalent interactions, heavily correlated systems, the chemistry of actinides, etc., the chemical bonding paradigm that works well in main-group elements loses power. Interestingly, the renaissance of long-time unattended methods, like valence bond theory, that carries an intrinsic interpretive toolbox, has also uncovered noteworthy disagreements with the traditional molecular pictures, and calls for new methods in the theory of chemical bonding based on orbital invariant descriptors.

It is, thus, a suitable time to gather experts across the different disciplines related to chemical bonding theory to showcase how the advent of new methods and the need to cope with unexplored bonding regimes is reshaping the field. Original research papers as well as reviews are welcome on new methodologies in orbital or real space, descriptors to cope with weakly bounded systems or with the spin structure of molecules, advances in conceptual density functional theory or the statistical distribution of electrons, energy decomposition schemes, etc. Applications of any of these methodologies to controversial cases or to bonding regimes far from the canon are particularly welcome, as are works comparing several possibly conflicting methodologies in a set of common systems.

Prof. Dr. Ángel Martín Pendás
Guest Editor

Manuscript Submission Information

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Keywords

theory of chemical bonding
energy decompositions
real space partitions
conceptual density functional theory
theoretical and computational chemistry
noncovalent interactions

Published Papers (7 papers)

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Research

12 pages, 2233 KiB

Open AccessArticle

Dual XH–π Interaction of Hexafluoroisopropanol with Arenes

by Le Lu and Ruimao Hua

Molecules 2021, 26(15), 4558; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26154558 - 28 Jul 2021

Cited by 6 | Viewed by 2640

Abstract

The dual XH (OH and CH) hydrogen-bond-donating property of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) and the strong dual XH–π interaction with arenes were firstly disclosed by theoretical studies. Here, the high accuracy post-Hartree–Fock methods, CCSD(T)/CBS, reveal the interaction energy of HFIP/benzene complex (−7.22 kcal/mol) and the contribution of the electronic correlation energy in the total interaction energy. Strong orbital interaction between HFIP and benzene was found by using the DFT method in this work to disclose the dual XH–π intermolecular orbital interaction of HFIP with benzene-forming bonding and antibonding orbitals resulting from the orbital symmetry of HFIP. The density of states and charge decomposition analyses were used to investigate the orbital interactions. Isopropanol (IP), an analogue of HFIP, and chloroform (CHCl₃) were studied to compare them with the classical OH–π, and non-classical CH–π interactions. In addition, the influence of the aggregating effect of HFIP, and the numbers of substituted methyl groups in benzene rings were also studied. The interaction energies of HFIP with the selected 24 common organic compounds were calculated to understand the role of HFIP as solvent or additive in organic transformation in a more detailed manner. A single-crystal X-ray diffraction study of hexafluoroisopropyl benzoate further disclosed and confirmed that the CH of HFIP shows the non-classical hydrogen-bond-donating behavior. Full article

(This article belongs to the Special Issue Advances in the Theory of Chemical Bonding)

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24 pages, 805 KiB

Open AccessArticle

Exceptionally Long Covalent CC Bonds—A Local Vibrational Mode Study

by Alexis Antoinette Ann Delgado, Alan Humason, Robert Kalescky, Marek Freindorf and Elfi Kraka

Molecules 2021, 26(4), 950; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26040950 - 11 Feb 2021

Cited by 24 | Viewed by 3602

Abstract

For decades one has strived to synthesize a compound with the longest covalent C−C bond applying predominantly steric hindrance and/or strain to achieve this goal. On the other hand electronic effects have been added to the repertoire, such as realized in the electron [...] Read more.

_{3 d}

form. Recently, negative hyperconjugation effects occurring in diamino-o-carborane analogs such as di-N,N-dimethylamino-o-carborane have been held responsible for their long C−C bonds. In this work we systematically analyzed CC bonding in a diverse set of 53 molecules including clamped bonds, highly sterically strained complexes such as diamondoid dimers, electron deficient species, and di-N,N-dimethylamino-o-carborane to cover the whole spectrum of possibilities for elongating a covalent C−C bond to the limit. As a quantitative intrinsic bond strength measure, we utilized local vibrational CC stretching force constants

k^{a}

(CC) and related bond strength orders BSO n(CC), computed at the

ω

B97X-D/aug-cc-pVTZ level of theory. Our systematic study quantifies for the first time that whereas steric hindrance and/or strain definitely elongate a C−C bond, electronic effects can lead to even longer and weaker C−C bonds. Within our set of molecules the electron deficient ethane radical cation, in D

_{3 d}

symmetry, acquires the longest C−C bond with a length of 1.935 Å followed by di-N,N-dimethylamino-o-carborane with a bond length of 1.930 Å. However, the C−C bond in di-N,N-dimethylamino-o-carborane is the weakest with a BSO n value of 0.209 compared to 0.286 for the ethane radical cation; another example that the longer bond is not always the weaker bond. Based on our findings we provide new guidelines for the general characterization of CC bonds based on local vibrational CC stretching force constants and for future design of compounds with long C−C bonds. Full article

(This article belongs to the Special Issue Advances in the Theory of Chemical Bonding)

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21 pages, 4418 KiB

Open AccessArticle

Ab Initio Dot Structures Beyond the Lewis Picture

by Michael A. Heuer, Leonard Reuter and Arne Lüchow

Molecules 2021, 26(4), 911; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26040911 - 09 Feb 2021

Cited by 4 | Viewed by 1913

Abstract

The empirical Lewis picture of the chemical bond dominates the view chemists have of molecules, of their stability and reactivity. Within the mathematical framework of quantum mechanics, all this chemical information is hidden in the many-particle wave function

Ψ

. Thus, to reveal [...] Read more.

Ψ

. Thus, to reveal and understand it, there is great interest in enhancing the Lewis model and connecting it to computable quantities. As has previously been shown, the Lewis picture can often be recovered from the probability density

{| Ψ |}^{2}

with probabilities in agreement with valence bond weights: the structures appear as most likely positions in the all-electron configuration space. Here, we systematically expand this topological probability density analysis to molecules with multiple bonds and lone pairs, employing correlated Slater-Jastrow wave functions. In contrast to earlier studies, non-Lewis structures are obtained that disagree with the prevalent picture and have a potentially better predictive capability. While functional groups are still recovered with these ab initio structures, the boundary between bonds and lone pairs is mostly blurred or non-existent. In order to understand the newly found structures, the Lewis electron pairs are replaced with spin-coupled electron motifs as the fundamental electronic fragment. These electron motifs—which coincide with Lewis’ electron pairs for many single bonds—arise naturally from the generally applicable analysis presented. An attempt is made to rationalize the geometry of the newly-found structures by considering the Coulomb force and the Pauli repulsion. Full article

(This article belongs to the Special Issue Advances in the Theory of Chemical Bonding)

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16 pages, 2727 KiB

Open AccessArticle

Energetics of Electron Pairs in Electrophilic Aromatic Substitutions

by Julen Munárriz, Miguel Gallegos, Julia Contreras-García and Ángel Martín Pendás

Molecules 2021, 26(2), 513; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26020513 - 19 Jan 2021

Cited by 4 | Viewed by 2880

Abstract

The interacting quantum atoms approach (IQA) as applied to the electron-pair exhaustive partition of real space induced by the electron localization function (ELF) is used to examine candidate energetic descriptors to rationalize substituent effects in simple electrophilic aromatic substitutions. It is first shown that inductive and mesomeric effects can be recognized from the decay mode of the aromatic valence bond basin populations with the distance to the substituent, and that the fluctuation of the population of adjacent bonds holds also regioselectivity information. With this, the kinetic energy of the electrons in these aromatic basins, as well as their mutual exchange-correlation energies are proposed as suitable energetic indices containing relevant information about substituent effects. We suggest that these descriptors could be used to build future reactive force fields. Full article

(This article belongs to the Special Issue Advances in the Theory of Chemical Bonding)

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19 pages, 3136 KiB

Open AccessFeature PaperArticle

NBO/NRT Two-State Theory of Bond-Shift Spectral Excitation

by Yinchun Jiao and Frank Weinhold

Molecules 2020, 25(18), 4052; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25184052 - 04 Sep 2020

Cited by 8 | Viewed by 2801

Abstract

We show that natural bond orbital (NBO) and natural resonance theory (NRT) analysis methods provide both optimized Lewis-structural bonding descriptors for ground-state electronic properties as well as suitable building blocks for idealized “diabatic” two-state models of the associated spectroscopic excitations. Specifically, in the framework of single-determinant Hartree-Fock or density functional methods for a resonance-stabilized molecule or supramolecular complex, we employ NBO/NRT descriptors of the ground-state determinant to develop a qualitative picture of the associated charge-transfer excitation that dominates the valence region of the electronic spectrum. We illustrate the procedure for the elementary bond shifts of S_N2-type halide exchange reaction as well as the more complex bond shifts in a series of conjugated cyanine dyes. In each case, we show how NBO-based descriptors of resonance-type 3-center, 4-electron (3c/4e) interactions provide simple estimates of spectroscopic excitation energy, bond orders, and other vibronic details of the excited-state PES that anticipate important features of the full multi-configuration description. The deep 3c/4e connections to measurable spectral properties also provide evidence for NBO-based estimates of ground-state donor-acceptor stabilization energies (sometimes criticized as “too large” compared to alternative analysis methods) that are also found to be of proper magnitude to provide useful estimates of excitation energies and structure-dependent spectral shifts. Full article

(This article belongs to the Special Issue Advances in the Theory of Chemical Bonding)

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26 pages, 3812 KiB

Open AccessFeature PaperArticle

Spin Density Topology

by Giovanna Bruno, Giovanni Macetti, Leonardo Lo Presti and Carlo Gatti

Molecules 2020, 25(15), 3537; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25153537 - 02 Aug 2020

Cited by 20 | Viewed by 4309

Abstract

Despite its role in spin density functional theory and it being the basic observable for describing and understanding magnetic phenomena, few studies have appeared on the electron spin density subtleties thus far. A systematic full topological analysis of this function is lacking, seemingly in contrast to the blossoming in the last 20 years of many studies on the topological features of other scalar fields of chemical interest. We aim to fill this gap by unveiling the kind of information hidden in the spin density distribution that only its topology can disclose. The significance of the spin density critical points, the 18 different ways in which they can be realized and the peculiar topological constraints on their number and kind, arising from the presence of positive and negative spin density regions, is addressed. The notion of molecular spin graphs, spin maxima (minima) joining paths, spin basins and of their valence is introduced. We show that two kinds of structures are associated with a spin–polarized molecule: the usual one, defined through the electron density gradient, and the magnetic structure, defined through the spin density gradient and composed in general by at least two independent spin graphs, related to spin density maxima and minima. Several descriptors, such as the spin polarization index, are introduced to characterize the properties of spin density critical points and basins. The study on the general features of the spin density topology is followed by the specific example of the water molecule in the ³B₁ triplet state, using spin density distributions of increasing accuracy. Full article

(This article belongs to the Special Issue Advances in the Theory of Chemical Bonding)

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12 pages, 2987 KiB

Open AccessArticle

Equilibrium Bond Lengths from Orbital-Free Density Functional Theory

by Kati Finzel

Molecules 2020, 25(8), 1771; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25081771 - 13 Apr 2020

Cited by 8 | Viewed by 3209

Abstract

This work presents an investigation to model chemical bonding in various dimers based on the atomic fragment approach. The atomic fragment approach is an ab-initio, parameter-free implementation of orbital-free density functional theory which is based on the bifunctional formalism, i.e., it uses both the density and the Pauli potential as two separate variables. While providing the exact Kohn-Sham Pauli kinetic energy when the orbital-based Kohn-Sham data are used, the bifunctional formalism allows for approximations of the functional derivative which are orbital-free. In its first implementation, the atomic fragment approach uses atoms in their ground state to model the Pauli potential. Here, it is tested how artificial closed-shell fragments with non-integer electron occupation perform regarding the prediction of bond lengths of diatomics. Such fragments can sometimes mimic the electronic structure of a molecule better than groundstate fragments. It is found that bond lengths may indeed be considerably improved in some of the tested diatomics, in accord with predictions based on the electronic structure. Full article

(This article belongs to the Special Issue Advances in the Theory of Chemical Bonding)

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