Exploring the Relationship between Reactivity and Electronic Structure in Isorhodanine Derivatives Using Computer Simulations.

The electronic structure and reactivity of 22 isorhodanine (IsRd) derivatives in the Diels-Alder reaction with dimethyl maleate (DMm) were investigated under two different environments (gas phase and continuous solvent CH3COOH), using free Gibbs activation energy, free Gibbs reaction energy, and frontier molecular orbitals to analyze their reactivity. The results revealed both inverse electronic demand (IED) and normal electronic demand (NED) characteristics in the Diels-Alder reaction and also provided insights into the aromaticity of the IsRd ring by employing HOMA values. Additionally, the electronic structure of the IsRd core was analyzed through topological examination of the electron density and electron localization function (ELF).

N-Activated 1,3-Benzoxazine Monomer as a Key Agent in Polybenzoxazine Synthesis.

A novel and successful application of ring-closing reactions of aminophenols has been proposed for the formation of a new type of 1,3-benzoxazine ionic derivatives. The optimization of the reaction and detailed computational studies have been reported for the estimation of heterocyclic ring stability and its further transformation, which is crucial in the polymerization process. The molecular structure of the obtained compounds has been fully characterized by applying X-ray analysis and spectroscopic methods.

Is It Conjugated or Not? The Theoretical and Experimental Electron Density Map of Bonding in -CHCHCOCH-C≡C-C≡C--CHCOCHCH.

The electron density of -CHCHCOCH-C≡CC≡C--CHCOCHCH has been investigated on the basis of single-crystal X-ray diffraction data collected to high resolution at 100 K and from theoretical calculations. An analysis of the X-ray data of the diyne showed interesting "liquidity" of electron distribution along the carbon chain compared to 1,2-diphenylacetylene. These findings are compatible with the results of topological analysis of Electron Localization Function (ELF), which has also revealed a larger (than expected) concentration of the electron density at the single bonds.

The nature of multiple boron-nitrogen bonds studied using electron localization function (ELF), electron density (AIM), and natural bond orbital (NBO) methods.

Local nature of the boron-nitrogen (BN) bonding with different formal multiplicities (B≡N, B=N, B-N) have been investigated for 25 experimentally established organoboron molecules in both real and the Hilbert space, using topological analysis of electron localization function (ELF), electron density (AIM), and natural bond orbital (NBO) method. Each BN bond has been represented (ELF) by the bonding disynaptic attractor V(B,N), with the basin electron population between 5.72e and 1.

The nature of the T=T double bond (T = B, Al, Ga, In) in dialumene and its derivatives: topological study of the electron localization function (ELF).

The local electronic structure of the Al=Al bond was studied in dialumene and derivatives of dialumene in which the Al atoms were substituted by B, Ga, or In atoms. DFT calculations were performed using the B3LYP, B3PW91, PBE0, M06-L, and M06-2X functionals. Topological analysis of the electron localization function described the covalent bonds mentioned above using the disynaptic basins V(B,B), V(Al,Al), V(Ga,Ga), and V(In,In).

Why are rhodanines less efficient reagents in Diels-Alder reactions than isorhodanines? A quantum chemical study.

The reactivity of the 5-arylidenerhodanine and 5-arylideneisorhodanine derivatives in reactions with dimethyl maleate was computationally studied at the DFT(M06-2X)/6-311+G(d,p) theory level. Eight stereoisomers of the reaction products were considered. The effect of the solvent was taken into account by means of the continuous and discrete models for acetic acid (PCM and three CHCOOH molecules).

On the nature of interactions in the F2 OXe(…) NCCH3 complex: Is there the Xe(IV)N bond?

Nature of the bonding in isolated XeOF2 molecule and F2 OXe(…) NCCH3 complexes have been studied in the gas phase (0 K) using Quantum Chemical Topology methods. The wave functions have been approximated at the MP2 and DFT levels of calculations, using the APFD, B3LYP, M062X, and B2PLYP functionals with the GD3 dispersion correction. The nature of the formal XeO bond in the XeOF2 monomer depends on the basis set used (all-electron vs.

Curly arrows meet electron density transfers in chemical reaction mechanisms: from electron localization function (ELF) analysis to valence-shell electron-pair repulsion (VSEPR) inspired interpretation.

Probing the electron density transfers during a chemical reaction can provide important insights, making possible to understand and control chemical reactions. This aim has required extensions of the relationships between the traditional chemical concepts and the quantum mechanical ones. The present work examines the detailed chemical insights that have been generated through 100 years of work worldwide on G.

The nature of inter- and intramolecular interactions in F2OXe(…)HX (X= F, Cl, Br, I) complexes.

Electronic structure of the XeOF2 molecule and its two complexes with HX (X= F, Cl, Br, I) molecules have been studied in the gas phase using quantum chemical topology methods: topological analysis of electron localization function (ELF), electron density, ρ(r), reduced gradient of electron density |RDG(r)| in real space, and symmetry adapted perturbation theory (SAPT) in the Hilbert space. The wave function has been approximated by the MP2 and DFT methods, using APF-D, B3LYP, M062X, and B2PLYP functionals, with the dispersion correction as proposed by Grimme (GD3). For the Xe-F and Xe=O bonds in the isolated XeOF2 molecule, the bonding ELF-localization basins have not been observed.

The DFT study on the reaction between benzaldehyde and 4-amine-4H-1,2,4-triazole and their derivatives as a source of stable hemiaminals and Schiff bases. Effect of substitution and solvation on the reaction mechanism.

Reaction mechanism for the benzaldehyde (ald) and 4-amine-4H-1,2,4-triazole (4at) has been investigated at the DFT (B3LYP)/6-31+G(d) computational level. Three transition states (TS) have been identified. The TS1 corresponds to hydrogen transfer from the NH2 group to the C = O bond and nucleophillic attack of the carbon atom from the aldehyde group on the nitrogen atom from the NH2 group in 4at.

Matrix-isolation and computational study of the HXeY⋯H2O complexes (Y = Cl, Br, and I).

The HXeY⋯H2O complexes (Y = Cl, Br, and I) are studied theoretically and experimentally. The calculations at the CCSD(T)/def2-TZVPPD level of theory predict two stable structures for Y = Cl and Br and one structure for Y = I, with interaction energies up to about -7 kcal mol(-1). In the experiments, we have identified several infrared absorption bands originating from the H-Xe stretching mode of these complexes in a xenon matrix.

Nature of the bonding in the AuNgX (Ng = Ar, Kr, Xe; X = F, Cl, Br, I) molecules. Topological study on electron density and the electron localization function (ELF).

Topological analysis of the electron localization function (ELF) has been carried out for the AuNgX (Ng = Ar, Kr, Xe; X = F, Cl, Br, I) molecules using the wave function approximated by the CCSD, MP2, and DFT(B3LYP, M062X) methods including zero-order regular approximation (ZORA). In the Ng-F bond, the bonding disynaptic attractor V(Ng,F) is missing; therefore, there are no signs of the covalent binding. The nature of the Au-Ng bond depends on the computational method used.

Electron localization function study on the chemical bonding in a real space for tetrahedrane, cubane, adamantane, and dodecahedrane and their perfluorinated derivatives and radical anions.

The nature of chemical bonding in caged cycloalkanes CnXn, CnFn(-•), (n = 4, 8, 20; X = H, F), and C10X16, C10F16(-•), (X = H, F) has been investigated using topological analysis of the ELF function, electron density, and the Laplacian of electron density at density functional theory (DFT) level. The bonding analysis performed for the perfluorinated radical anion of dodecahedrane (C20F20(-•)), bestowing an additional electron, shows an unexpected local maximum of the ELF inside the carbon cage. The presence of such an attractor confirms the sigma stellation concept presented by Irikura (J.

Effects of xenon insertion into hydrogen bromide. Comparison of the electronic structure of the HBr···CO2 and HXeBr···CO2 complexes using quantum chemical topology methods: electron localization function, atoms in molecules and symmetry adapted perturbation theory.

Quantum chemistry methods have been applied to study the influence of the Xe atom inserted into the hydrogen-bromine bond (HBr → HXeBr), particularly on the nature of atomic interactions in the HBr···CO2 and HXeBr···CO2 complexes. Detailed analysis of the nature of chemical bonds has been carried out using topological analysis of the electron localization function, while topological analysis of electron density was used to gain insight into the nature of weak nonbonding interactions. Symmetry-adapted perturbation theory within the orbital approach was applied for greater understanding of the physical contributions to the total interaction energy.

Reaction of atomic hydrogen with formic acid.

We study the reaction of atomic hydrogen with formic acid and characterize the radical products using IR spectroscopy in a Kr matrix and quantum chemical calculations. The reaction first leads to the formation of an intermediate radical trans-H2COOH, which converts to the more stable radical trans-cis-HC(OH)2via hydrogen atom tunneling on a timescale of hours at 4.3 K.

Following the molecular mechanism for the NH3 + LiH → LiNH2 + H2 chemical reaction: a study based on the joint use of the quantum theory of atoms in molecules (QTAIM) and noncovalent interaction (NCI) index.

The molecular mechanism for the NH3 + LiH → LiNH2 + H2 reaction has been elucidated by the combined use of quantum theory of atoms in molecules (QTAIM) and noncovalent interactions (NCI) index. The topology of the electron density, obtained by QTAIM/NCI, is able to identify the evolution of strong and weak interactions, recovering the bonding patterns along the reaction pathway. Thus, the combination of these two techniques is a useful and powerful tool in the study of chemical events, providing new strategies to understand and visualize the molecular mechanisms of chemical rearrangements.

Tuning of character of the N-O bond in HONO from covalent to protocovalent by different types of intramolecular interactions.

Quantum-chemical calculations of the H-O-N=O molecule in the equilibrium and transition states and the complexes of the HONO with BH3, study of the intramolecular interactions using NBO theory, and investigation of the electron distribution on the basis of topological analysis of the ELF function clearly indicate the influence of the n-π* conjugation and n-σ* hyperconjugation interactions on a par with exchange repulsion of lone pairs the character of the N-O bond. It is shown that repulsion between lone pairs of oxygen and nitrogen atoms causes the elongation of the N-O bond only but character of this bond remains covalent. The interaction between lone pair of the terminal oxygen atom and antibonding orbital of the N-O bond (n-σ* hyperconjugation) coincides with influence of repulsion and reinforces it changing the character of the N-O bond from covalent to protocovalent.

Spectroscopic and computational characterization of the HCO···H2O complex.

The complexes of HCO with water are prepared in a Kr matrix and characterized by IR spectroscopy with the aid of ab initio calculations. The calculations at the UCCSD(T)/aug-cc-pVTZ level of theory predict three structures of the HCO···H2O complex. In the "linear" structure I, a hydrogen atom of water interacts with the oxygen atom of HCO.

FONO: a difficult case for theory. The ELF and ELI-D topological studies on the chemical bonding using correlated wavefunctions.

The complicated nature of the chemical bonding in cis and trans isomers of F-O-N=O is discussed based on the results obtained from the topological analysis of electron localization function (η) (ELF), electron localizability index (Y(D)(σ)), and electron density (ρ). The calculations have been performed for correlated wavefunctions using the CCSD and CASSCF methods. The F-O1 bond with non-bonding basins, V(F) and V(')(O1), belongs to the protocovalent type (η,Y(D)(σ)) and its total population ranges between 0.

New insight into the electronic structure of iron(IV)-oxo porphyrin compound I. A quantum chemical topological analysis.

The electronic structure of iron-oxo porphyrin π-cation radical complex Por(·+) Fe(IV)=O (S-H) has been studied for doublet and quartet electronic states by means of two methods of the quantum chemical topology analysis: electron localization function (ELF) η(r) and electron density ρ(r). The formation of this complex leads to essential perturbation of the topological structure of the carbon-carbon bonds in porphyrin moiety. The double C=C bonds in the pyrrole anion subunits, represented by pair of bonding disynaptic basins V(i=1,2)(C,C) in isolated porphyrin, are replaced by single attractor V(C,C)(i=1-20) after complexation with the Fe cation.

How a Quantum Chemical Topology Analysis Enables Prediction of Electron Density Transfers in Chemical Reactions. The Degenerated Cope Rearrangement of Semibullvalene.

Recent works on the reaction mechanism for the degenerated Cope rearrangement (DCR) of semibullvalene (SBV) in the ground state prompted us to investigate this complex rearrangement in order to assign experimentally observed contrast features in the simulated electron distribution. We present a joint use of the electron localization function (ELF) and Thom's catastrophe theory (CT) as a powerful tool to analyze the electron density transfers along the DCR. The progress of the reaction is monitored by the structural stability domains of the topology of ELF, while the change between them is controlled by turning points derived from CT.

Electronic fluxes during Diels-Alder reactions involving 1,2-benzoquinones: mechanistic insights from the analysis of electron localization function and catastrophe theory.

By means of the joint use of electron localization function (ELF) and Thom's catastrophe theory, a theoretical analysis of the energy profile for the hetero-Diels-Alder reaction of 4-methoxy-1,2-benzoquinone 1 and methoxyethylene 2 has been carried out. The 12 different structural stability domains obtained by the bonding evolution theory have been identified as well as the bifurcation catastrophes (fold and cusp) responsible for the changes in the topology of the system. This analysis permits finding a relationship between the ELF topology and the evolution of the bond breaking/forming processes and electron pair rearrangements through the reaction progress in terms of the different ways of pairing up the electrons.

High kinetic stability of HXeBr upon interaction with carbon dioxide: HXeBr···CO2 complex in a xenon matrix and HXeBr in a carbon dioxide matrix.

We investigate the conditions when noble-gas hydrides can be found in real environments and report on the preparation and identification of the HXeBr···CO(2) complex in a xenon matrix and HXeBr in a carbon dioxide matrix. The H-Xe stretching mode of the HXeBr···CO(2) complex in a xenon matrix is observed at 1557 cm(-1), showing a spectral shift of +53 cm(-1) from the HXeBr monomer. The calculations at the CCSD(T)/aug-cc-pVTZ-PP(Xe,Br) level of theory give two stable structures for the HXeBr···CO(2) complex with frequency shifts of +55 and +103 cm(-1), respectively.

Electron localization function study on intramolecular electron transfer in the QTTFQ and DBTTFI radical anions.

The unsymmetrical distribution of the unpaired electron in the ground state of the DBTTFI(•-) radical anion (bi(6-n-butyl-5,7-dioxo-6,7-dihydro-5H-[1,3]dithiolo[4,5-f]isoindole-2-ylidene) is theoretically predicted using the M06-2X/6-31+G(d,p) level of calculations. The results are additionally confirmed by single point calculations at B3LYP/aug-cc-pVTZ, LC-ωPBE/aug-cc-pVTZ, and M06-2X/aug-cc-pVTZ levels. DBTTFI, containing the TTF (tetrathiafulvalene) fragment, may be used in the construction of organic microelectronic devices, similarly to the radical anion of QTTFQ.

Comparative density functional theory and post-Hartree-Fock (CCSD, CASSCF) studies on the electronic structure of halogen nitrites ClONO and BrONO using quantum chemical topology.

In this paper, the electronic structures of cis- and trans-ClONO and BrONO are studied at the CCSD∕aug-cc-pVTZ, CASSCF(14,12)/aug-cc-pVTZ, and B3LYP/aug-cc-pVTZ computational levels. For the Cl-O bond, topological analysis of the electron density field, ρ(r), shows the prevalence of the shared-electron type bond (∇(2)ρ((3,-1)) < 0). The Br-O bond, however, represents the closed-shell interaction (∇(2)ρ((3,-1)) > 0).