Concept Of Electronegativity Research Articles

A simple method for calculating atomic charges in charged molecular systems of biochemical interest

A previously developed method for calculating atomic charge in neutral molecules is modified so as to account for charged molecular species. The method is based on the orbital electronegativity (EN) concept and utilizes an EN equalization principal. Since only one linear equation is required per bond in the molecule, the scheme is extremely simple to use and thus is readily applicable to larger molecules of interest to biochemistry. Atom charge results are compared to ab initio calculations as well as experimental data from NMR and X-ray diffraction studies. It is shown that the method compares very well even with higher level theoretical methods for a variety of charged molecules including alanine and protonated adenine. It is also shown that NMR chemical shift data for charged amino acids are correlated quite well with atomic charges from the present method. In addition charges obtained from X-ray diffraction data for both ionic alanine and 2′-deoxycytidine-5′-monophosphate are also reproduced very well.

X-ray K-absorption studies of glassy Ge22Se68M10(M = Ag, Cd, In, Pb)

Abstract X-ray K-absorption studies of glassy Ge22Se78 and Ge22Se68M10 (M = Ag, Cd, In, Pb) have been made in order to understand the nature of bonding of metallic atoms in ternary alloys. The edge shift is found to be dependent on the difference in electronegativity between the metallic atoms and the Ge or Se atoms. The results are in agreement with Pauling's concept of electronegativity and indicate that the nature of the bonds in these glasses is iono-covalent in character as found in many crystalline solids.

Structural studies of glassy semiconducting Se80 − xTe20Inx alloys

AbstractThe shift of the K‐absorption edge (ΔEK) was measured in Se80‐xTe20Inx, where 0 ≤ x ≤ 20. It is observed that the K‐edge of Se shifts progressively towards the lower energy side as the In concentration increases from 0 to 15 at.‐%. However, at higher concentrations, the relative shift starts to decrease. The results are in accordance with the Pauling concept of electronegativity and indicate that the nature of the bonds is iono‐covalent in these glasses, as found in many crystalline solids. The composition dependence of the edge shift is also discussed in terms of the structure of the Se‐Te system.

X-ray spectroscopic studies in glassy semiconducting Ge 20Se 80 and Ge 20Se 80- xIn x alloys

The shift of the K-absorption edge (Δ E K) is measured in ternary alloys of Ge 20Se 80- x In x with respect to the binary Se 80Ge 20 alloy. The results indicate that the K-edge of Se progressively shifts towards the lower energy side as the concentration increases from 0 to 10 at%. However at a higher concentration of In ( χ > 15), the negative shift starts decreasing. The results are in accordance with Pauling's concept of electronegativity and indicate that the nature of bonds is iono-covalent in character in these glasses, as found in many crystalline solids. The composition dependence of Δ E K is also discussed in terms of the structure of Ge-Se system.

Study of K‐absorption edge of selenium in the glassy semiconducting Se100−xInx system

AbstractThe shift of the K‐absorption edge (δEk) was measured in Se100‐xInx binary system where 0 ≤x ≤ 30. The K‐edge of Se progressively shifted toward the lower energy side as the In concentration increased from 0 to 15 at.‐%. However, at higher concentrations, the relative shift started to decrease. The results are in accordance with Pauling's concept of electronegativity and indicate that the nature of the bonds is iono‐covalent in these glasses, as found in many crystalline solids. The composition dependence of the edge shift is also discussed in terms of the structure of Se.

電気陰性度の考え方の変遷

電気陰性度の考え方の変遷

Volcano-shaped curves in heterogeneous catalysis

An analytic equation for the volcano-shaped curves in derived from the Polanyi relation. It is generally applicable to catalytic reactions that can be represented by two kinetically significant steps. The shape and size of the volcano depends on the degree of nonuniformity of the adsorbate binding state and on the extent to which the thermodynamic driving force affects the kinetics of a reaction step. In heterogeneous catalysis, Sabatier's principle is a kinetic guideline that needs to be modified in accordance with the nonuniformity. The present methodology can be useful for the design of optimum catalysts as well as for elucidating the reaction mechanism at the molecular level. The Polanyi parameter which appears as a reaction order directly reflects the chemical stability of the adsorbates and the nature of the reactant-catalyst electronic interactions as shown through an approach founded on electronegativity concepts.

Three-Dimensional Periodic Table Of Elements Proposed

Recently, Princeton University physical chemistry professor Leland C. Allen had to relearn inorganic chemistry so he could teach it to undergraduates. That experience gave Allen a few ideas that, if accepted by the chemistry community, would change some basic tenets of inorganic chemistry, including the form of the periodic table of elements. Allen proposes a redefinition of one of the most basic quantities in chemistry—electronegativity, the tendency of an atom to attract electrons [ J. Am. Chem. Soc ., 111 , 9003 (1989)]. In addition, he says that electronegativity, which he now calls valence-shell energy, is the third dimension of the periodic table. To bring the concept of electronegativity into more widespread use Allen has translated valence-shell energy into a quantum mechanical operator that can be employed in computational chemistry programs. Furthermore, he proposes a simple equation that corrects for the effects of electronegativity in formal charge calculations [ J. Am. Chem. Soc ., 111 ,9115(...

X-ray K-absorption studies in glassy Se80Te10 and Se80Te18M10 (M=Ag, Cd, In and Sb)

X-ray K-absorption studies have been made in glassy Se80Te10 and Se80Te18M10 (M=Ag, Cd, In and Sb) to understand the bonding of metallic atoms in ternary alloys. The authors find that the Se-K-edge shifts towards the negative energy side in all the ternary alloys compared with binary Se80Te10 alloy. Moreover, the edge shift is found to increase as the difference in electronegativity between metallic atoms and Se increases. These results are in agreement with Pauling's concept of electronegativity and indicate that the nature of bonds is iono-covalent in character in these glasses, as found in many crystalline solids.

Correlation between electronegativity and superconductivity.

This paper brings out one of the striking features exhibited by all oxide superconductors. It is found the irrespective of the value of ${T}_{c}$, the average electronegativity \ensuremath{\chi} of all the oxide superconductors found up until now lie between 2.5 and 2.65 in the Pauling's scale and this is considered to be one of the criteria for oxide materials to be considered superconductors. This narrow range is in contrast to the elemental superconductors whose values lie in a broad range from 1.3 to 1.9. Further, the pressures required to drive some of the elemental metals to become superconductors have been calculated on the basis of their electronegativity values. The pressures so obtained agree well with the experimental observations and those calculated on the basis of band theory. The average electronegativity of A--15 Chevrel-phase superconductors are also given. Based on the concept of electronegativity the other oxide systems which are likely to become superconductors have been suggested.

What can metal-ligand bonding energetics teach us about stoichiometric and catalytic organometallic chemistry?

Abstract

ChemInform Abstract: Absolute Electronegativity and Hardness: Application to Inorganic Chemistry

The recent concepts of absolute electronegativity, {chi}, and absolute hardness, {eta}, are briefly reviewed. Experimental values for a large number of molecules and radicals are presented. The values are shown to be in good agreement with the known chemical behavior, both as to nucleophilic-electrophilic properties and as to rates of reaction. Applications are also given for the use of empirical rank orders of the local hardness, {bar {eta}}. The uses of {chi} and {eta} are consistent with frontier orbital theory. To make meaningful comparisons in a series of molecules, it is necessary that these orbitals remain the same. Also it is necessary that the observed I and A values of the molecules relate to the appropriate frontier orbitals. 39 refs., 10 tabs.

Principles of electronegativity Part I. General nature

The concept of electronegativity has been modified, expanded, and debated. The concept can be used to help students gain valuable insights and understanding of the cause-and-effect relationship between atomic structure and compound properties. This is the first in a series of articles that explores the important concept of electronegativity.

Absolute electronegativity and hardness: application to inorganic chemistry

The recent concepts of absolute electronegativity, {chi}, and absolute hardness, {eta}, are briefly reviewed. Experimental values for a large number of molecules and radicals are presented. The values are shown to be in good agreement with the known chemical behavior, both as to nucleophilic-electrophilic properties and as to rates of reaction. Applications are also given for the use of empirical rank orders of the local hardness, {bar {eta}}. The uses of {chi} and {eta} are consistent with frontier orbital theory. To make meaningful comparisons in a series of molecules, it is necessary that these orbitals remain the same. Also it is necessary that the observed I and A values of the molecules relate to the appropriate frontier orbitals. 39 refs., 10 tabs.

Absolute electronegativity and hardness correlated with molecular orbital theory

The concepts of absolute electronegativity, chi, and absolute hardness, eta, are incorporated into molecular orbital theory. A graphic and concise definition of hardness is given as twice the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Useful correlations can now be made between chemical behavior, visible-UV absorption spectra, optical polarizability, ionization potentials, and electron affinities.

Thermal activation of ammonium forms of Y zeolites. I. T.p.d., i.r., and catalytic investigations of the deammoniation of NH 4NaY zeolites

The deammoniation of a series of NH 4NaY zeolites of various exchange degrees has been studied thermodesorptometrically using different methods in order to obtain independent statements about the kinetics of the desorption process. In all cases at least two overlapping NH 3 peaks have been observed, the separation of which was possible by means of a temperature stop method. These two peaks could be ascribed to the desorption of NH 3 from OH groups of different kinds. The assignment of the peaks was possible by comparison of the desorptogrammes with i.r. spectra in the range of the OH stretching vibrations and with results of catalytic but-1-ene isomerization measurements. The calculated activation energies for NH 3 desorption seem to be suitable for the characterization of the acid strength of the OH groups. They were compared with partial charges of the hydrogen, calculated by means of the Sanderson electronegativity concept.

Thermal activation of ammonium forms of Y zeolites. III. T.p.d., n.m.r., i.r. and catalytic investigation of MnNH 4Na, NH 4Na and MnNaYzeolites

MnNH 4Na, NH 4Na, and MnNaY zeolites and their corresponding H forms, produced by thermal treatment of the ammonium forms, were studied by means of t.p.d., n.m.r., i.r. and catalytic experiments. In addition, calculations of the partial charge of hydrogen were carried out on the basis of the Sanderson electronegativity concept. A comparison of t.p.d, and n.m.r. results shows similar amounts of acidic OH groups on a MnHNaY and an HNaY sample of equal exchange degrees of H +. The evaluation of the deammoniation and dehydroxylation peaks of t.p.d., the i.r. spectroscopic frequency shift of the hydrogen bond between OH groups and trifluoroacetone, and the catalytic acidity concerning the but-1-ene isomerization, refer to a particular state of the Mn 2+ ions and to an essentially higher acid strength o; the MnHNaY sample as compared with MnNaY and HNaY, respectively. The latter finding is supported by the calculations according to the Sanderson concept.

Coordination chemistry of higher oxidation states. 10 [1]. Oxofluoroanions of osmium(VIII) [OsO 4F 2] 2− and [OsO 3F 3] −

Trioxotrifluoroosmates(VIII) M[OsO 3F 3] (M = Cs, Rb, K) have been prepared by direct combination of OsO 3F 2 and the appropriate alkali fluoride MF. The reaction of OsO 4 with M′F (M′ = Cs, Rb) in aqueous solution produces the tetraoxodifluoroosmates(VIII) M′ 2[OsO 4F 2]. On the basis of their vibrational spectra the assignment of a fac (C 3v) structure to [OsO 3F 3] − and a cis (C 2v) to [OsO 4F 2] 2− is proposed. The electronic spectra of the anions have been recorded and are interpreted using the optical electronegativity concept.

Interaction between zeolites and cluster compounds. Part 2.—Thermal decomposition of iron pentacarbonyl on zeolites

Thermal decomposition in a thermobalance of Fe(CO)5 adsorbed on alkali-metal, hydrogen-Y, dealuminated Y, L and omega zeolites proceeds stepwise via slow decarbonylation at low and high temperatures, separated by a fast endothermic reaction. Average CO/Fe ratios have been determined after each step. From i.r. results the former intermediates are assigned to species bearing bridging CO, whereas reaction products with CO/Fe < 1 are associated with highly unsaturated carbonyl clusters in strong interaction with the zeolite.The thermal stability of zeolite/Fe(CO)5 adducts as well as of the intermediates increases with the electron-donor properties of the matrix and can be rationalized using the Sanderson electronegativity concept. Iron loadings ranging from 2.4 wt % in zeolite L up to 10 wt % with NaY and HY are obtained by decomposition in inert atmosphere. Under vacuum conditions loss of metal up to 50% is observed. Metallic iron clusters are the final decomposition products in alkali-metal zeolites, as probed by NO adsorption. In HY part of the metallic iron is oxidized to FeII ions, which are located at cation positions.

On definition of electronegativity within the framework of MO methods

The possibility of generalization of the electronegativity concept to valence states of atom in molecule has been studied by semiempirical CNDO and INDO approximations. It is shown that the concept of electronegativity as the property of a given atom in molecule can be defined only on the basis of the simplest CNDO approximation.