Phase separation near the charge neutrality point in FeSe1-xTex crystals with x < 0.15

Our study of FeSe$ _ {1-x}$Te$ _ {x}$ crystals with x $<$ 0.15 shows that the phase separation in these compositions occurs into phases with a different stoichiometry of iron. This phase separation may indicate structural instability of the iron plane in the studied range of compositions. We tentatively propose an explanation of the structural instability of the iron plane in the studied layered compounds in terms of the possible change in the bond polarity and the peculiarity of the direct $d-d$ exchange in the iron plane in the framework of the basic phenomenological description such as the Bethe-Slater curve. With this approach, when the distance between iron atoms is close to the value at which the sign of the magnetic exchange for some $d$ orbitals changes, structural and electronic instability can occur. Anomalies in the crystal field near the point of charge neutrality can also be a significant component of this instability.

Site-selective C(sp3)-H Functionalizations Mediated by Hydrogen Atom Transfer Reactions via α-Amino/α-Amido Radicals

Amines and amides, as N-containing compounds, are ubiquitous in pharmaceutically active scaffolds, natural products, agrochemicals and peptides. Amides in nature bear key responsibility for three-dimensional structure, such as in proteins. Structural modifications to amines and amides, especially at their positions α- to N, bring about profound changes in biological activity oftentimes leading to more desirable pharmacological profiles of small molecule drugs. A number of recent developments in synthetic methodology for the functionalizations of amines and amides omit the need of directing groups or pre-functionalizations, achieving direct activation of the otherwise benign C(sp3)-H bond. Among these, hydrogen atom transfer (HAT) has proven a very powerful platform for the selective activation of amines and amides to their α-amino and α-amido radicals, which can then be employed to furnish C-C and C-X (X=heteroatom) bonds. The ability to both form these radicals and control their reactivity in a site-selective manner is of utmost importance for such chemistries to witness applications in late-stage functionalization. Therefore, this review captures contemporary HAT strategies to realize chemo- and regioselective amine and amide α-C(sp3)-H functionalization, based on bond strength, bond polarity, reversible HAT equilibria, traceless electrostatic directing auxiliaries and steric effects of in situ-generated HAT agents.

Chemical Bonding 1: Basic Concepts

Chemical Bonding I: Basic Concepts examines general ideas of chemical bonding between atoms and ions and how this bonding affects the chemical properties of the elements. An overview of Lewis symbols, Lewis structures and the octet rule is presented including the role of valence electrons in ionic and covalent bonding. The energy changes that accompany ionic bond formation are also discussed with emphasis on lattice energy. The chapter covers guidelines and general procedures for writing Lewis structures or electron dot formulas for molecular compounds and polyatomic ions. The concepts and applications of resonance, formal charge and exceptions to the octet rules are presented, along with coverage of the relationship between bond polarity and electronegativity.

A New Mechanism of the Selective Photodegradation of Antibiotics in the Catalytic System Containing TiO2 and the Inorganic Cations

The mechanism of sulfisoxazole (SFF) selective removal by photocatalysis in the presence of titanium (IV) oxide (TiO2) and iron (III) chloride (FeCl3) was explained and the kinetics and degradation pathways of SFF and other antibiotics were compared. The effects of selected inorganic ions, oxygen conditions, pH, sorption processes and formation of coordination compounds on the photocatalytic process in the presence of TiO2 were also determined. The Fe3+ compounds added to the irradiated sulfonamide (SN) solution underwent surface sorption on TiO2 particles and act as acceptors of excited electrons. Most likely, the SFF degradation is also intensified by organic radicals or cation organic radicals. These radicals can be initially generated by reaction with electron holes, hydroxyl radicals and as a result of electron transfer mediated by iron ions and then participate in propagation processes. The high sensitivity of SFF to decomposition caused by organic radicals is associated with the steric effect and the high bond polarity of the amide substituent.

Solid-state electronegativity of atoms: new approaches

Electronegativities (EN) of 65 elements (H to Bi, except lanthanides and noble gases, plus U and Th) in solids were derived from various observed parameters, namely, bond energies in solids, structural geometry, work functions and force constants, yielding a set of internally consistent values. The solid-state electronegativities are generally lower than the conventional (`molecular') values, due to different coordination numbers and electronic structure in a solid versus a molecule; the decrease is stronger for metals than for non-metals, hence binary compounds have a wider EN difference and higher bond polarity (ionicity) in the solid than in the molecular (gaseous) state. Under high pressure, the ENs of metals increase and those of non-metals decrease, the binary solid becomes less polar and can ultimately dissociate into elements.

Using electrostatic potential maps as visual representations to promote better understanding of chemical bonding

Static visual representations (VRs) of chemical structures are necessary for an understanding of chemical bonding, a topic which continues to lead to learning difficulties and misconceptions for many students. The efficacy and problems associated with the use of VRs of chemical structures and chemical bonding in the form of electrostatic potential maps resulting from accurate quantum mechanical calculations are the subject of this study, which involved a sample of first year, second semester students, studying the elective course “Science Education” (N = 31). Students distinguished between nonpolar and polar covalent bonding, however, they encountered difficulties with concepts related to ionic bonding. Most students did not employ multistructural thinking (in the sense of the SOLO taxonomy), when providing explanations about the variation of bond polarity. Persistence of a covalent-ionic bond dichotomy was apparent, while for some, ions can be involved in both ionic and covalent bonding. Many students preferred to use their established high school knowledge. On a positive note, many students were clearly affected by the information provided by the colored VRs. Finally, the minimal experience of our students with these VRs leads us to believe that a more systematic and extensive coverage would be likely to produce improved outcomes.

Thermochemical electronegativities of the elements

Electronegativity is a key property of the elements. Being useful in rationalizing stability, structure and properties of molecules and solids, it has shaped much of the thinking in the fields of structural chemistry and solid state chemistry and physics. There are many definitions of electronegativity, which can be roughly classified as either spectroscopic (these are defined for isolated atoms) or thermochemical (characterizing bond energies and heats of formation of compounds). The most widely used is the thermochemical Pauling’s scale, where electronegativities have units of eV−1/2. Here we identify drawbacks in the definition of Pauling’s electronegativity scale—and, correcting them, arrive at our thermochemical scale, where electronegativities are dimensionless numbers. Our scale displays intuitively correct trends for the 118 elements and leads to an improved description of chemical bonding (e.g., bond polarity) and thermochemistry.

DFT Study of the Structural, Electronic, Bonding Nature, NBO Analysis, and Thermodynamic Properties of Halogenated (F, Cl, Br) and Heteroatom (O, N, S) doped Cyclopropane

Background: The chemistry of cyclopropanes has been widely studied over the years as a result of its high reactivity which is due to its highly strained ring. The cyclopropane ring is highly significant in drug research as the 10th most frequently found ring in small molecules and as such, there is a need for research to improve further the reactivity of cyclopropanes in natural products and pharmaceuticals. In this work, we present an extremely comprehensive and detailed investigation on a variety of properties of cyclopropane including Geometrical properties, bonding nature, bond polarity index (BPI), natural bond orbitals (NBO), orbital charge analysis, Density of states (DOS), molecular electrostatic potential (MEP), UV-spectral analysis, electron ionization, affinity and accompanied process, local reactivity parameters and the effects of substitution of heteroatoms Nitrogen (N-doped C3H8), Oxygen (S-doped C3H8) and Sulphur (S-doped C3H8) each in the place of carbon atom (otherwise known as doping) and also the substitution effects of Fluorine, Chlorine and Bromine each on one hydrogen atom in cyclopropane molecule (halogenation) and investigate how it chemically affects the properties outlined above. Results: It is observed from conceptual (CDFT) results that S-doped C3S has the highest reactivity of all the molecules studied. The UV-spectral analysis also predicts doped C3S as the molecule that gives the highest Bathochromic shift of all the molecules. Some other properties studied also give us the most potential sites for electrophilic and nucleophilic attack by electrophiles and nucleophiles. The NBO investigation revealed the strongest stabilization to the cyclopropane molecule for the heteroatoms follow the trend C3S<C3N<C3O. It is also observed that for the halogens the strongest stabilization for the cyclopropane molecule follows the trend C3Br<C3Cl<C3F<C3. The strong intra-molecular hyperconjugation interaction of the 2-centered bond (BD) and CR electrons of C-C anti C-C bond in the ring leads to stabilization of the cyclopropane ring as evident from the order perturbation energy analysis. Conclusion: The results obtained from the research will help scientists further improve on the reactivity of cyclopropanes as a motif in drug discovery through substitution (halogenation) and doping with heteroatoms (O, S, N)

Effect of Hydrogen Absorption on the Composition of the Amorphous Alloys Surface Layers

Hydrogen absorption leads to redistribution of the components of the surface layer of the amorphous alloy Fe73.8Si12.7B9.4Nb3.2Cu noncontact side, while the amorphous structure of this layer is preserved. The type of the micro-groups Fey Six changes in such a way that the ratio y: x decreases (to less than 1) and the chemical bond polarity decreases, as well. After degassing, the surface layer composition becomes similar to those before hydrogenation. The loss of the mechanical stability of the amorphous ribbon is accompanied by the formation of the micro-groups Fey Six with a decreased ratio of y: x.