The Molecular Electron Density Theory: Modern Theoretical Insights on Reactivity in Organic Chemistry

A special issue of Chemistry (ISSN 2624-8549). This special issue belongs to the section "Theoretical and Computational Chemistry".

Deadline for manuscript submissions: closed (31 October 2022) | Viewed by 4384

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Department of Organic Chemistry, University of Valencia, Dr. Moliner 50, Burjassot, 46100 Valencia, Spain
Interests: molecular electron density theory (MEDT); theoretical organic chemistry; chemical concepts; structure and reactivity; molecular mechanisms and selectivities; quantum-chemical topology
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Institute of Organic Chemistry & Technology, Cracow University of Technology, Warszawska 24, 31-155 Krakow, Poland
Interests: cycloaddition reactions; nitrocompounds; cycloaddition; heterocycles; reaction mechanisms; organic reactivity; DFT calculations
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Guest Editor
Department of Organic Chemistry, University of Valencia (UV), Burjassot, 46100 Valencia, Spain
Interests: Molecular Electron Density Theory (MEDT); physical-organic chemistry; chemical concepts and reactivity; molecular mechanisms; reaction selectivities; pseudocyclic reactions; chemical bond and chemical structure; conceptual DFT; Quantum Topology of electron distribution functions such as electron density and electron localization function (ELF)
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Since the end of the last century, the development of the Conceptual Density Functional Theory (CDFT), together with the implementation of pertinent quantum chemical tools—which allow topological analysis of the molecular electron density such as the Quantum Theory of Atoms in Molecules (QTAIM), the Electron Localization Function (ELF) and Non-Covalent Interactions (NCIs)—have permitted the study of organic chemical reactivity based solely on electron-density analysis.

These quantum chemical tools inform us of the electronic structure of all species participating in an organic reaction, and thus allow us to understand chemical organic reactivity from a modern point of view based on the analysis of electron density. This rejects the model developed in the 1960s based on the analysis of molecular orbitals.

The present Special Issue will collect modern theoretical studies of reactivity in Organic Chemistry based only on the analysis of the molecular electron density, with the aim of establishing and spreading a new perspective on chemical organic reactivity.

Prof. Dr. Luis R. Domingo
Prof. Dr. Radomir Jasiński
Dr. Mar Ríos-Gutiérrez
Guest Editors

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Keywords

  • molecular elecron density theory
  • conceptual density functional theory
  • topology of the molecular elecron density
  • electron localization function
  • atom in molecules
  • non-covaklmet interactions
  • chemical organic reactivity
  • reaction mechanisms
  • excited states

Published Papers (2 papers)

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Research

30 pages, 8606 KiB  
Article
The (E, Z) Isomerization of C-methoxycarbonyl-N-aryl Chlorohydrazones
by Giorgio Molteni, Fausto Cargnoni, Raffaella Soave and Alessandro Ponti
Chemistry 2022, 4(4), 1624-1653; https://doi.org/10.3390/chemistry4040106 - 02 Dec 2022
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Abstract
Since chlorohydrazones are planar molecules, it is in principle possible to distinguish between their E and Z stereoisomers. Chlorohydrazones are known to preferentially assume the Z configuration around the C=N double bond, and their (E, Z) isomerization is almost suppressed [...] Read more.
Since chlorohydrazones are planar molecules, it is in principle possible to distinguish between their E and Z stereoisomers. Chlorohydrazones are known to preferentially assume the Z configuration around the C=N double bond, and their (E, Z) isomerization is almost suppressed at room temperature. The lack, or rather the difficulty, of such an isomerization has been conveniently addressed by the in-depth theoretical study of seven C-methoxycarbonyl-N-aryl chlorohydrazones (aryl = phenyl, 4-chlorophenyl, 4-bromophenyl, 4-iodophenyl, 2-chlorophenyl, 2-bromophenyl, and 2-iodophenyl). DFT ωB97M-D4/cc-pVTZ calculations of these C-methoxycarbonyl-N-aryl chlorohydrazones, supported by the XRD determination of the molecular structure, provided a complete picture of the isomerization processes in the studied compounds. The analysis of the energetics, molecular geometry, and electronic structure (the latter in the framework of the Quantum Theory of Atoms In Molecules) showed that the Z isomers are thermodynamically favored because, within the low-energy planar isomers with extensive π conjugation, the electrostatic interactions between the dipoles of the C–O, C–Cl, and N–H bonds overcome the stabilization induced by the N–H ··· O bond present in the E isomers. We confirmed that the (E, Z) isomerization occurs by the umklapp mechanism, in which the –NHAr moiety rotates in the molecular plane towards a linear C=N–N configuration and then proceeds to the other isomer. The (E, Z) isomerization is very slow at room temperature because the umklapp interconversion has high barriers (≈110 kJ/mol) despite the extended π electron delocalization present in the transition state. Full article
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18 pages, 3456 KiB  
Article
Unveiling the Chemistry of Higher-Order Cycloaddition Reactions within the Molecular Electron Density Theory
by Luis R. Domingo, Mar Ríos-Gutiérrez and Patricia Pérez
Chemistry 2022, 4(3), 735-752; https://doi.org/10.3390/chemistry4030052 - 26 Jul 2022
Cited by 6 | Viewed by 2223
Abstract
The higher-order cycloaddition (HOCA) reaction of tropone with cyclopentadiene (Cp) has been studied within the Molecular Electron Density Theory. The Electron Localization Function (ELF) analysis of the electronic structure of tropone and Cp characterizes the structural behaviors of the two conjugated unsaturated systems, [...] Read more.
The higher-order cycloaddition (HOCA) reaction of tropone with cyclopentadiene (Cp) has been studied within the Molecular Electron Density Theory. The Electron Localization Function (ELF) analysis of the electronic structure of tropone and Cp characterizes the structural behaviors of the two conjugated unsaturated systems, while the conceptual DFT reactivity indices classify tropone as a strong electrophile and Cp as a strong nucleophile participating in polar cycloaddition reactions of reverse electron density flux. Eight competitive reaction paths have been characterized for this cycloaddition reaction. The most favorable one allowing the formation of the formal out [6 + 4] cycloadduct has an activation enthalpy of 16.2 kcal·mol−1, and the reaction is exothermic by −21.4 kcal·mol−1. This HOCA reaction, which takes place through a non-concerted two-stage one-step mechanism, presents high stereo-, pseudocyclic- and regioselectivities, explaining the exclusive formation of the experimental [6 + 4] cycloadduct. While the most favorable nucleophilic attack of Cp on most electrophilic C2 positions of tropone accounts for regioselectivities, the favorable electrostatic interactions present between the Cp framework and the negatively charged O8 oxygen of tropone account for the stereo- and pseudocyclic selectivities. Despite the symmetry of the two reagents, this HOCA reaction takes place via a highly asynchronous transition state structure as a consequence of the most favorable two-center interactions taking place between the electrophilic C2 center of tropone and the nucleophilic C9 center of Cp. Full article
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