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Quantum chemical simulations were conducted to elucidate the electronic structure of the 2-azaallenyl radical cation, a key intermediate in several [3 + 2]-cycloadditions initiated by the oxidation of 2H-azirine. We propose one additional Lewis structure in resonance with the commonly accepted two Lewis structures for the model system of 1,3-diphenyl-2-azaallenyl radical cation, drawn from comprehensive theoretical data including molecular shape, bond order analysis, partial atomic charges, and spin densities. In addition to the ground state chemistry, the chemical structure of excited state species can be also understood with these three Lewis structures. Theoretical data imply that a newly suggested one mainly accounts for the ground state structure, and the excited state structure is better represented by the previously reported ones. Our claim is further bolstered by the prediction of the excited state geometries of the dicationic and neutral species. This research presents the extended set of Lewis structures for a better understanding electronic structure of 2-azaallenyl radical cation. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations have been carried out at the BP86/def2‐SVP level on Ge8(Sit‐butyl2methyl)6 (1) and the bonding situation has been analyzed with a variety of methods. The calculated equilibrium geometry of 1 is in good agreement with the reported x‐ray structure analysis. The D3 correction for dispersion interactions as a sum of pairwise attractions leads to an overestimate of the effect of dispersion forces. Calculations at BP86‐D3(BJ)/def2‐SVP give shorter bonds for Ge(I)−Ge(I) than for Ge(0)−Ge(I), which is in contrast to the experimental values and the BP86/def2‐SVP results. The NBO analysis suggests that the best Lewis structure of 1 has lone‐pair orbitals at the Ge(0) atoms with occupation numbers of 1.70 e. A lone‐pair character at Ge(0) albeit with less weight is also suggested by the shape of the HOMO, which is an antibonding orbital between the Ge(0) atoms with small contributions from the Ge(I) atoms. The LUMO of 1 is the corresponding bonding combination of the Ge(0) AOs, which can be explained with the reluctance of the heavier main‐group atoms to s/p hybridization of the valence orbitals. The calculated bond order values suggest significant direct Ge(0)−Ge(0) interactions. This is supported by the shape of the HOMO and by the results of EDA‐NOCV calculations. The deformation densities and the orbitals associated with the pairwise orbital interaction show that there is a direct charge flow between the Ge(0) atoms of the two fragments, but it is not completely separated from the Ge(0)−Ge(I) and Ge(I)−Ge(I) bond formation. The QTAIM calculations suggest that 1 has a cubic structure with a cage critical point but not a bond critical point for the Ge(0)−Ge(0) interactions. The dispersion interactions of the large substituents in 1 have a significant influence on the stability of the compound. [ABSTRACT FROM AUTHOR]

Quantum chemical calculations have been carried out at the BP86/def2‐SVP level on Ge8(Sit‐butyl2methyl)6 (1) and the bonding situation has been analyzed with a variety of methods. The calculated equilibrium geometry of 1 is in good agreement with the reported x‐ray structure analysis. The D3 correction for dispersion interactions as a sum of pairwise attractions leads to an overestimate of the effect of dispersion forces. Calculations at BP86‐D3(BJ)/def2‐SVP give shorter bonds for Ge(I)−Ge(I) than for Ge(0)−Ge(I), which is in contrast to the experimental values and the BP86/def2‐SVP results. The NBO analysis suggests that the best Lewis structure of 1 has lone‐pair orbitals at the Ge(0) atoms with occupation numbers of 1.70 e. A lone‐pair character at Ge(0) albeit with less weight is also suggested by the shape of the HOMO, which is an antibonding orbital between the Ge(0) atoms with small contributions from the Ge(I) atoms. The LUMO of 1 is the corresponding bonding combination of the Ge(0) AOs, which can be explained with the reluctance of the heavier main‐group atoms to s/p hybridization of the valence orbitals. The calculated bond order values suggest significant direct Ge(0)−Ge(0) interactions. This is supported by the shape of the HOMO and by the results of EDA‐NOCV calculations. The deformation densities and the orbitals associated with the pairwise orbital interaction show that there is a direct charge flow between the Ge(0) atoms of the two fragments, but it is not completely separated from the Ge(0)−Ge(I) and Ge(I)−Ge(I) bond formation. The QTAIM calculations suggest that 1 has a cubic structure with a cage critical point but not a bond critical point for the Ge(0)−Ge(0) interactions. The dispersion interactions of the large substituents in 1 have a significant influence on the stability of the compound. [ABSTRACT FROM AUTHOR]

. This paper describes simple rules that can minimize the uncertainties in explaining the process of finding the hybridization of a p-block central atom and the geometrical structure in a covalent molecule or an ion. The current rules to predict the hybridization and geometrical structure are based on Lewis’s structure, Pauli’s principle, covalent bond theories and the VSEPR model. This is a practical and easy way used by teachers and students.

Chemists use one set of orbitals when comparing to a structural formula, hybridized AOs or NBOs for example, and another for reasoning in terms of frontier orbitals, MOs usually. Chemical arguments can frequently be made in terms of energy and/or electron density without the consideration of orbitals at all. All orbital representations, orthogonal or not, within a given function space are related by linear transformation. Chemical arguments based on orbitals are really energy or electron density arguments; orbitals are linked to these observables through the use of operators. The Valency Interaction Formula, VIF, offers a system of chemical reasoning based on the invariance of observables from one orbital representation to another. VIF pictures have been defined as one-electron density and Hamiltonian operators. These pictures are classified in a chemically meaningful way by use of linear transformations applied to them in the form of two pictorial rules and the invariance of the number of doubly, singly, and unoccupied orbitals or bonding, nonbonding, and antibonding orbitals under these transformations. The compatibility of the VIF method with the bond pair – lone pair language of Lewis is demonstrated. Different electron lone pair representations are related by the pictorial rules and have stability understood in terms of Walsh’s rules. Symmetries of conjugated ring systems are related to their electronic state by simple mathematical formulas. Description of lone pairs in conjugated systems is based on the strength and sign of orbital interactions around the ring. Simple models for bonding in copper clusters are tested, and the bonding of O2 to Fe(II) in hemoglobin is described. Arguments made are supported by HF, B3LYP, and MP2 computations.

Topological analysis of the Electron Localisation Function (ELF) within the framework of Quantum Chemical Topology (QCT) has been applied to study the nature of the boron–oxygen bonds. A series of 16 compounds has been chosen, with the experimental B O bond length in the range of 1.481 Å (B O)–1.179 Å (B O). Topological results obtained for the DFT(M062X), DFT(B3LYP), MP2 and CCSD(T) optimised geometrical structures show that all the boron–oxygen bonds in the investigated compounds are described by the disynaptic bonding basin, V(B,O). All these bonds have a covalent-polarised character. The mean electron population of V(B,O) varies from 1.6e (B(OH) 4 − ) to about 3.5e (HN CH CH CH NH B O). The polarity index values, p BO, lie between 0.77 (ClBO) and 0.89 (H 2 BOCH 3 ), thus all boron–oxygen bonds are essentially polarised by the oxygen atom. According to the Lewis formula, four types of the bonds have been recognised. These are: a single bond with a mixture of the ionic hybrid (B O, B + O − ), a single bond (B O), a single bond with a small contribution of the dative O→B bond (B O) and a single bond with a large contribution of the dative O→B bond (depleted B O bonds). There is a clear distinction between a group of 11 molecules chosen for this study, with the basin population value of the boron–oxygen bond between 1.6e and 2.4e, and the HB O, FB O, ClB O, HN CH CH CH NH B O and trans-[(Me3P)2BrPt(B O)] molecules that exhibit the basin population in the range: 3.3e–3.5e. The second group was postulated to have a triple bond, B O, but this statement has not been confirmed by our research. [ABSTRACT FROM AUTHOR]

The maxima of squared electronic wave functions [ABSTRACT FROM AUTHOR]

Abstract: The Arabidopsis thaliana genome contains a small group of bipartite F-box proteins, consisting of an N-terminal F-box domain and a C-terminal domain sharing sequence similarity with Nictaba, the jasmonate-induced glycan-binding protein (lectin) from tobacco. Based on the high sequence similarity between the C-terminal domain of these proteins and Nictaba, the hypothesis was put forward that the so-called F-box-Nictaba proteins possess carbohydrate-binding activity and accordingly can be considered functional homologs of the mammalian sugar-binding F-box or Fbs proteins which are involved in proteasomal degradation of glycoproteins. To obtain experimental evidence for the carbohydrate-binding activity and specificity of the A. thaliana F-box-Nictaba proteins, both the complete F-box-Nictaba sequence of one selected Arabidopsis F-box protein (in casu At2g02360) as well as the Nictaba-like domain only were expressed in Pichia pastoris and analyzed by affinity chromatography, agglutination assays and glycan micro-array binding assays. These results demonstrated that the C-terminal Nictaba-like domain provides the F-box-protein with a carbohydrate-binding activity that is specifically directed against N- and O-glycans containing N-acetyllactosamine (Galβ1-3GlcNAc and Galβ1-4GlcNAc) and poly-N-acetyllactosamine ([Galβ1-4GlcNAc]n) as well as Lewis A (Galβ1-3(Fucα1-4)GlcNAc), Lewis X (Galβ1-4(Fucα1-3)GlcNAc, Lewis Y (Fucα1-2Galβ1-4(Fucα1-3)GlcNAc) and blood type B (Galα1-3(Fucα1-2)Galβ1-3GlcNAc) motifs. Based on these findings one can reasonably conclude that at least the A. thaliana F-box-Nictaba protein encoded by At2g02360 can act as a carbohydrate-binding protein. The results from the glycan array assays revealed differences in sugar-binding specificity between the F-box protein and Nictaba, indicating that the same carbohydrate-binding motif can accommodate unrelated oligosaccharides. [Copyright &y& Elsevier]

Chemists use one set of orbitals when comparing to a structural formula, hybridized AOs or NBOs for example, and another for reasoning in terms of frontier orbitals, MOs usually. Chemical arguments can frequently be made in terms of energy and/or electron density without the consideration of orbitals at all. All orbital representations, orthogonal or not, within a given function space are related by linear transformation. Chemical arguments based on orbitals are really energy or electron density arguments; orbitals are linked to these observables through the use of operators. The Valency Interaction Formula, VIF, offers a system of chemical reasoning based on the invariance of observables from one orbital representation to another. VIF pictures have been defined as one-electron density and Hamiltonian operators. These pictures are classified in a chemically meaningful way by use of linear transformations applied to them in the form of two pictorial rules and the invariance of the number of doubly, singly, and unoccupied orbitals or bonding, nonbonding, and antibonding orbitals under these transformations. The compatibility of the VIF method with the bond pair - lone pair language of Lewis is demonstrated. Different electron lone pair representations are related by the pictorial rules and have stability understood in terms of Walsh's rules. Symmetries of conjugated ring systems are related to their electronic state by simple mathematical formulas. Description of lone pairs in conjugated systems is based on the strength and sign of orbital interactions around the ring. Simple models for bonding in copper clusters are tested, and the bonding of O2 to Fe(II) in hemoglobin is described. Arguments made are supported by HF, B3LYP, and MP2 computations. [ABSTRACT FROM AUTHOR]

• Characterization of a new crystal compound was studied using X-ray crystallography and computational techniques. • Crystal system of the title molecule was monoclinic with space group C2/c (#15). • HOMA, NBO and hirshfeld surface analysis of the studied compound were calculated. • Structural and electronic properties of the studied molecule were discussed in detail. • The studied compound was hard molecule and it has lower chemical reactivity and higher kinetic stability. A new crystal compound, 2‑bromo-4‑chloro-6-[(2‑ hydroxy -5- methylanilino) methylidene cyclohexa-2,4-dienone (Compound 1) was experimentally characterized by infrared, UV–Visible spectroscopy and single crystal X-ray diffraction technique. We report herein the synthesis, characterization of single crystal structure, DFT, natural bond orbital, linear and nonlinear optical properties studies of compound 1. The experimental data of UV–Visible, IR and X-ray and calculated data obtained from TD-DFT and DFT methods were compared and discussed in detail. The UV–Visible, IR and X-ray data revealed that the studied compound exists as keto-amine form. Compound 1 was crystallized in the monoclinic crystal system in the space group C2/c (#15) with chemical formula C 14 H 11 BrClNO 2. The crystal geometry of compound 1 was stabilized by hydrogen bond and weak π–π interactions. The 97.58% Lewis structure and 2.42% non-Lewis structure were found in the studied molecular system. [ABSTRACT FROM AUTHOR]

Topological analysis of electron localisation function (ELF) has been used to study the nature of the BX (X = F, Cl) bonds in 26 molecules. Twelve small molecules with formal BX, BX, and BX bonds and 14 organoboron molecules with the BCl bond from the Cambridge Structural Database have been studied using CCSD, DFT(M062x) methods. As the V(B,F) basin population for the investigated molecules is smaller than 4 and 6e, the existence of BX, BX bonds is not confirmed. The results show higher polarity of BF bonds as compared to the BCl bonds. Electronic structure of selected molecules has been discussed from the ELF‐topological perspective. A possibility of multiple B...X, BX, and BX (X = F, Cl) bonds has been thoroughly researched using topological analysis of ELF function for the DFT(M062x) and CCSD(T) optimized structures (26). [ABSTRACT FROM AUTHOR]