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Understanding and Dispersion Interaction using the Non-covalnet Index.

Understanding the Woodward Hoffmann Rules using Changes in the Electron Density (No Orbitals necessary

Stacked complexes made of phenol and substituted benzenes are studied via MP2 calculations in order to investigate the influence of the stacking interaction on the acidity of phenol. Aqueous-phase proton affinities have been computed and converted to pKa values using a calibration procedure involving a set of substituted phenols. Both T-shaped and parallel-displaced conformations lead to an appreciable decrease in the pKa, with the largest effect found for T-shaped arrangements. Local and global DFT based reactivity descriptors are used to analyze the effect of the stacking partner as well as the interaction between the aromatic rings.

Li+ Speciation and the use of 7Li/6Li isotope ratios for ancient climate monitoring.

Four simple density functional theory methods are investigated to assess how well they can describe subtle variations in negative vertical electron affinities arising due to the successive fluorination of ethylene, where the magnitude of the variations is well below the absolute accuracy of the methods. Three of the approaches (two based on Koopmans’ theorem and one using a potential wall) are able to describe the trends in the affinities using both compact and very diffuse basis sets. The best results are obtained using the potential wall. The fourth approach uses a conventional energy difference evaluation, which is only applicable when the basis set is compact; the breakdown upon addition of diffuse functions is strikingly illustrated. The results are interpreted in terms of the spatial extent of the relevant orbitals and the signs and values of the orbital energies. The study highlights the potential predictive value of simple DFT methods for describing trends in negative affinities.

The unexpected nucleophilic reactivity of free-radicals generated from alpha-iodoketones is reported; two different procedures, either employing tin or the more environmentally acceptable ethylsulfone-based coupling reagent 5c have been developed.

The Woodward Hoffmann rules regained by Conceptual Densify Functional Theory

On the Applicability of the Local Softness and Hardness

Conceptual DFT gives sharp definitions for many long-known, but rather vaguely defined chemical concepts. In this study DFT-based reactivity indices are applied to silylenes in order to elucidate the relationships among their properties: stability, acid-base, and spin properties, nucleophilicity and electrophilicity. On the basis of a detailed, comparative analysis of previously published data, it is shown that the properties of simple silylenes can be tuned by varying one single factor, the pi-electron donating ability of the substituents of the silicon atom leading to well-characterized and systematic changes in the stability/reactivity pattern of the molecule. In order to test the model a series of new compounds are studied: including CH3SiR (where R = CH3, NH2, OH and SH), Si(Si(CH3)3)2, Si(CF3)2 and benzo-, pyrido-, pyridazo-, and pyrimido-anellated-1,3,2lambda2-diazasiloles.

The properties of various electron-deficient germylenes and stannylenes are investigated using density functional theory (DFT). The dominant electrophilic character of these divalent group IV compounds is demonstrated by computed DFT-based reactivity descriptors. Next, the interaction of selected model dihalogenated germylenes and stannylenes (GeX2 and SnX2, with X = F, Cl, Br, I) with a series of potential aromatic π-donors is studied; computed classical donor–acceptor σ-interactions with strong Lewis bases serve as a reference. In addition, natural bond orbital analyses were performed in order to study the interactions at the orbital level, consistently indicating that the most important interaction for the π-complexations is the overlap of the formal empty p-orbital on the germanium or the tin atom and the π-orbitals of the aromatic rings. Additional information is obtained from the extent of charge transfer from the π-donors toward the divalent tin and germanium compounds. The existence of a complexat...

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Conceptual Density Functional Theory based Intrinsic Radical Stabilities: Application to Substituted Silylenes and p-benzynes". Invited contribution to the special issue "Concepts in DFT"

Woodward Hofmann Rules in Conceptual Density Functional Theory : Initial Hardness Response

A simple method was recently proposed [D. J. Tozer and F. De Proft, J. Chem. Phys., 2007, 127, 034108] for performing explicit density functional theory (DFT) calculations on temporary anions. The excess electron in the anion is bound by a potential wall, the position of which is determined by a single parameter lambda, chosen to reproduce an approximate, theoretical negative electron affinity in the corresponding neutral. In the present study, the system-dependence of lambda and the sensitivity of the negative affinities to this parameter are investigated for 34 organic molecules. The results demonstrate that the system-dependent lambda values can be replaced by a global, average value, with minimal effect on the affinities. It follows that the orbitals, electron density, and other properties of a temporary anion can be determined from a single DFT calculation on that anion, using a large, diffuse basis set. As an illustration, singly occupied molecular orbitals and spin densities are determined for the anions of guanine and adenine nucleobases. Despite the use of a diffuse basis set, the method yields quantities that are localised in the molecular framework, associated with vertical electron affinities of -1.2 eV and -0.8 eV, respectively.

Organotin(IV)Derivatives of Some O,C,O-Chelating Ligands, Part 2

Solvation of Graphene: Thermodynamic Aspects

Reactivity of dicoordinated Stannylones (Sn(O))vs. Stannylenes (Sn(II)): Investigation using DFT based Reactivity Indices.

In this study, for the first time inverse design was applied to search for the intrinsically most stable radical system in a predefined chemical space of enormous size by scanning in a rational way that entire chemical space. The focus was predominantly on thermodynamic stabilization effects, such as stabilization through resonance. Two different properties were optimized: a newly introduced descriptor called the radical delocalization value and the intrinsic stability via a previously established bond dissociation enthalpy model. The thiadiazinyl radical was chosen as case study of this new approach of inverse design in stable radical chemistry. The resulting optimal structure is found to be highly stable, intrinsically more so than other well-known stable radicals, such as verdazyls and N,N-diphenyl-N′-picrylhydrazyl, and even rivaling the intrinsic stability of nitrogen monoxide.

The intrinsic electrophilic reactivity of linear acenes up to octacene was investigated by using interaction energy potentials and their components, namely Pauli repulsion, orbital interaction, and electrostatic interaction potentials using the Ziegler–Rauk decomposition scheme. We found that the shared regions above C1 and C2 of the outer ring are slightly more attractive towards an incoming electrophile than the inner ring secondary carbon atoms, mostly due to a more advantageous electrostatic interaction. This result agrees with the stability order of prereactive π complexes formed between anthracene and the electrophilic HCl. Decomposition potentials determined in the bond formation regime indicate that longer acenes become more reactive because of the increasing orbital interaction. In addition, the orbital interaction potentials, which represent the overall effect of the high lying reactive orbital, exhibit straightforward patterns, predicting strongly preferred inner ring secondary carbon atoms over outer ring carbon atoms. Such an orbital-interaction controlled regioselectivity shows up in the total interaction energy potentials when the electrostatic interaction is scaled down, predicting the functionalization of acenes with electrophiles on the inner secondary carbon atoms, in agreement with the experimental regioselectivity. Upon analyzing the stability of transition states for the addition of HCl to anthracene, the Pauli repulsion shows up to be an important factor in controlling the stability of the transition states and favoring functionalization along the central C9 and C10 positions to outer ring carbon atoms. The resonance stabilization concept, which is generally accepted to account for the regioselectivity of higher acenes, could not be evidenced by our analysis.

2-Picolyl azide reacts with cis-[PtCl2(DMSO)2] to form the diimino complex [Pt(II)Cl2{NH═C(H)Py}] with subsequent dinitrogen liberation. The formation of the latter complex is scrutinized in a combined experimental and theoretical analysis. We establish in silico that the transformation involves a highly reactive intermediate containing a Pt═N double bond formed after the extrusion of N2 from the azide functionality. The prerequisites for N2 liberation and for the stabilization of the nitrene-related intermediate are analyzed in detail.

An analysis of the global and local aromaticity was made for a series of hydrogenated fullerenes of the type C60H2n (n = 1 6) at ab initio HF(HartreenFock)/3-21G level of theory, the isomers considered being obtained with an octahedral addition pattern. The relation between this addition pattern and the magnetic properties was established, showing low aromatic regions to be preferred for addition. These results show that local aromaticity, as shown by nucleus-independent chemical shift, can be used to predict addition sites in these systems. In many chemical reactions, fullerenes behave as electron defi cient alkenes [1n3]. From its chemical properties, no global aromaticity is expected for C60, and computed magnetic properties of closed-shell fullerenes show overall diamagnetic behaviour with sugnifi cant vatiations in local ring currents [4n10]. After computation studies of the chemical reactivity of hydrofullerenes and substituted hydrofullerenes of the type C60Hn [11] ,C 60HR [12] and C70HR [13], the delocalisation that occured upon deprotonation of these systems has already been analysed [13,14] .W ith C 60H2 and C60Ht-Bu already being proven belonging to the most acidic hydrocarbons [15,16], further modelling of the chemical behaviour can be achieved upon modifi cation of the functional group R, and serve as starting material for further synthesis [17]. Based on the expansion of C60 upon its three rotational axes, three distinct series of cylindrical fullerenes can be constructed. The C5; C3 and C2 axes yield armchair, zigzag and chiral cylinders (icapped nanotubesi) of signatures (5,5), (9,0) and (8,2), respectively [18]. These series have provided useful test sets for exploration of electronic structure [19n21] and elastic properties [22]. Also global and local aromaticities were recently described for these series [23]. Local aromaticity of a ring is described by its ability to support diamagnetic ring (i. e. diatropic) currents, which can be described by the nucleus-independent chemical shift (NICS )[ 24]. A more generally applicable model for local aromaticity, the so-called PentagonnProximity Model, could be derived, where the positioning of the pentagons in the system is seen to infl uence the whole pattern of local aromaticity for each system, as shown by ab initio NICS calculations. The overall magnetic structure can be understood in terms of a mechanical assembly of the counter-rotating rim and hub currents characteristics of circulene system such as coronene and corannulene [25]. In this work, we analyse the global and local aromaticity upon multiple octahedral addition of hydrogen to C60 in the series C60H2n (n = 1 6). The relation between the local aromaticity, as denoted by NICS, with the addition pattern is highlighted. After describing the computational details in Sect. 2, results will be detailed in Sect. 3 for the global (Sect. 3.1.) and the local aromaticities (Sect. 3.2.), and the relation with the addition pattern is discussed (Sect. 3.3.). Conclusions will be drawn in Sect. 4, together with the perspectives for further investigations.

A Quantum Similarity Study of Atoms: Constructing a Hardness Based Similarity Index

A New View On The Spectrochemical and Nephelauxetic Series On The Basis of Spin Polarized Conceptual DFT

The Spin Polarised Linear Response from Density Functional Theory: Theory and Application to Atoms

Out-of-plane shear and out-of plane Yang's modulus of double layer graphene

The Shannon entropy of the ratio of electron density and the number of electrons, shape function entropy, is reported for the atoms He-Ac within the non-relativistic exchange-only optimized effective potential model. The derivative of the shape function entropy with electron number at constant external potential is related to an integral containing the difference between the average Fukui function and the shape function weighted by the logarithm of electron density. The trends in the shape function entropy, its spin analogue and the corresponding derivatives with electron number reveal interesting periodic behaviour.

We continue a series of papers in which the chemical importance of the linear response kernel chi(r, r') of conceptual DFT is investigated. In previous contributions (J. Chem. Theory Comput. 2010, 6, 3671; J. Phys. Chem. Lett. 2010, 1, 1228; Chem. Phys. Lett. 2010, 498, 192), two computational methodologies were presented and it was observed that the linear response kernel could serve as a measure of electron delocalisation, discerning inductive, resonance and hyperconjugation effects. This study takes the analysis one step further, linking the linear response kernel to the concept of aromaticity. Based on a detailed analysis of a series of organic and inorganic (poly) cyclic molecules, we show that the atom-condensed linear response kernel discriminates between aromatic and non-aromatic systems. Moreover, a new quantitative measure of aromaticity, termed the para linear response (PLR) index, is introduced. Its definition was inspired by the recent work published around the para delocalisation index (PDI). Both indices are shown to correlate very well, which emphasises the linear response kernel's value in the theoretical description of aromaticity The authors thank Jens Top for performing preliminary calculations. N. S. acknowledges the Research Foundation-Flanders (FWO) for a position as research assistant. F. D. P. and P. G. thank the FWO and the Vrije Universiteit Brussel for continuous financial support. M. S. thanks the Spanish MICINN (CTQ2008-03077/BQU and CTQ2011-23156 projects) and the Catalan DIUE (2009SGR637 and ICREA Academia 2009 prize)

Recent advances in alkaline earth (Ae) metal hydrogenation catalysis have broadened the spectrum of potential catalysts to include candidates from the main group, providing a sustainable alternative to the commonly used transition metals. Although Ae-amides have already been demonstrated to catalyze hydrogenation of imines and alkenes, a lucid understanding of how different metal/ligand combinations influence the catalytic activity is yet to be established. In this article, we use linear scaling relationships and molecular volcano plots to assess the potential of the Ae metal-based catalysts for the hydrogenation of alkenes. By analyzing combinations of eight metals (mono-, bi-, tri-, and tetravalent) and seven ligands, we delineate the impact of metal-ligand interplay on the hydrogenation activity. Our findings highlight that the catalytic activity is majorly determined by the charge and the size of the metal ions. While bivalent Ae metal cations delicately regulate the binding and the release of the reactants and the products, respectively, providing the right balance for this reaction, ligands play only a minor role in determining their catalytic activity. We show how volcano plots can be utilized for the rapid screening of prospective Ae catalysts to establish a guideline to achieve maximum activity in facilitating the hydrogenation process.The online version of this article at 10.1007/s11244-021-01480-7.