Hypervalency and Aromaticity

Baerends, E.J. [Promotor]Bickelhaupt, F.M. [Copromotor

Hypervalence and the delocalizing versus localizing propensities of H-3(-), Li-3(-), CH5- and SiH5-

Lithium and silicon have the capability to form hypervalent structures, such as L

Can Variations of (HNMR)-H-1 Chemical Shifts in Benzene Substituted with an Electron-Accepting (NO2)/Donating (NH2) Group be Explained in Terms of Resonance Effects of Substituents?

The classical textbook explanation of variations of (HNMR)-H-1 chemical shifts in benzenes bearing an electron-donating (NH2) or an electron-withdrawing (NO2) group in terms of substituent resonance effects was examined by analyzing molecular orbital contributions to the total shielding. It was found that the -electronic system showed a more pronounced shielding effect on all ring hydrogen atoms, relative to benzene, irrespective of substituent +R/-R effects. For the latter, this was in contrast to the traditional explanations of downfield shift of nitrobenzene proton resonances, which were found to be determined by the sigma-electronic system and oxygen in-plane lone pairs. In aniline, the +R effect of NH2 group can be used to fully explain the upfield position of meta-H signals and partly the upfield position of para-H signals, the latter also being influenced by the sigma-system. The position of the lowest frequency signal of ortho-Hs was fully determined by sigma-electrons.This is peer-reviewed version of the following article: Baranac-Stojanović, M. Can Variations of 1H NMR Chemical Shifts in Benzene Substituted with an Electron-Accepting (NO2)/Donating (NH2) Group Be Explained in Terms of Resonance Effects of Substituents? Chemistry - An Asian Journal 2018, 13 (7), 877–881. [https://doi.org/10.1002/asia.201800137]Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3181

Observations of tetrel bonding between sp3-carbon and THF

We report the direct observation of tetrel bonding interactions between $sp^{3}$-carbons of the supramolecular synthon 3,3-dimethyl-tetracyanocyclopropane (1) and tetrahydrofuran in the gas and crystalline phase. The intermolecular contact is established via σ-holes and is driven mainly by electrostatic forces. The complex manifests distinct binding geometries when captured in the crystalline phase and in the gas phase. We elucidate these binding trends using complementary gas phase quantum chemical calculations and find a total binding energy of −11.2 kcal mol$^{−1}$ for the adduct. Our observations pave the way for novel strategies to engineer $sp^{3}$-C centred non-covalent bonding schemes for supramolecular chemistry

Aromaticity and Antiaromaticity in 4-, 6-, 8-, and 10-Membered Conjugated Hydrocarbon Rings

Recently, we presented a molecular orbital (MO) model of aromaticity that explains, in terms of simple orbital-overlap arguments, why benzene (

Aromaticity and Bond Declocalization inHeterocyclic and inorganic benzene analogues

Recently, we presented a molecular orbital (MO) model of aromaticity that explains, in terms of simple orbital-overlap arguments, why benzene (

Aromaticity: Molecular-Orbital Picture of an Intuitive Concept

Geometry is one of the primary and most direct indicators of aromaticity and antiaromaticity: a regular structure with delocalized double bonds (e.g., benzene) is symptomatic of aromaticity, whereas a distorted geometry with localized double bonds (e.g., 1,3-cyclobutadiene) is characteristic of antiaromaticity. Here, we present a molecular-orbital (MO) model of aromaticity that explains, in terms of simple orbital-overlap arguments, why this is so. Our MO model is based on accurate Kohn–Sham DFT analyses of the bonding in benzene, 1,3-cyclobutadiene, cyclohexane, and cyclobutane, and how the bonding mechanism is affected if these molecules undergo geometrical deformations between regular, delocalized ring structures, and distorted ones with localized double bonds. We show that the propensity of the π electrons is always, that is, in both the aromatic and antiaromatic molecules, to localize the double bonds, against the delocalizing force of the σ electrons. More importantly, we show that the π electrons nevertheless decide about the localization or delocalization of the double bonds. A key component of our model for uncovering and resolving this seemingly contradictory situation is to analyze the bonding in the various model systems in terms of two interpenetrating fragments that preserve, in good approximation, their geometry along the localization/delocalization modes