Relative Bond Strengths Research Articles

Viscosities of melts in the Na 2OFeOFe 2O 3SiO 2 system and factors controlling relative viscosities of fully polymerized silicate melts

The viscosity-temperature relationships of nine melts in the Na 2OFeOFe 2O 3SiO 2 system (in equilibrium with air) have been measured in the temperature range of 1450–800°C, using the concentric cylinder method. 57Fe Mössbauer spectra were obtained on quenched samples and show that all melts with ≥ 20 mole% ferrite component contain ≥ 95% Fe as tetrahedrally-coordinated ferric ions. The compositions investigated lie along the SiO 2NaFeO 2 and Na 2Si 4O 9Na 6Fe 4O 9 joins. The viscosities of m decrease strongly with decreasing silicate content along these joins. In contrast, the temperature dependence of viscosity does not vary significantly along these joins. Comparison with equivalent melt compositions (related by the trivalent cation exchange operators AlFe −1, BFe −1 and GaFe −1) in the Na 2OAl 2O 3SiO 2, Na 2OB 2O 3SiO 2 and Na 2O-Ga 2O 3 viscosities decrease in the order aluminosilicate > ferrosilicate, (galliosilicate ?) > borosilicate. Thp electronegativities of the trivalent cations are inversely correlated with the relative viscosities of melts in these systems. Similarly, the electronegativities of network-stabilizing cations are inversely correlated with melt viscosity for alkali and alkaline-earth aluminosilicate melt systems. The variation in the viscosity of tectosilicate melts is correlated with estimated average T-O-T bond angles, and exothermic heats of solution of quench glasses. Structural controls of viscosity discussed are tetrahedral ordering and relative bond strengths. The acmite component in natural, peralkaline, silicic volcanics will not contribute directly to high melt viscosities for these lavas.

Calculation of the relative stability and strengths of particular bonds in polyphenylene sulphides

The energies of atomization, formation and strength of particular bonds of 22 polymer structures based on polyphenylene sulphides and polyphenylenes are calculated within the framework of an interacting bond model. The effect of isomerism and substituents on the bond strength along the polymer backbone is discussed. The polydibenzothiophene and polythianthrene structures are the most stable forms of polyphenylene sulphides. On substitution of hydrogen atoms in polyphenylene sulphides by phenyl groups the strength of the CS bond along the main polymer backbone is changed.

ChemInform Abstract: Electrostatic Potentials and Relative Bond Strengths of Some Nitro‐ and Nitrosoacetylene Derivatives

Abstract : A computational analysis of the structures and properties of a group of substituted acetylenes has been carried out by means of an ab initio self-consistent-field molecular orbital procedure (GAUSSIAN 82). The molecules studied were acetylene, its singly and doubly substituted nitro and nitroso derivatives, methylnitroacetylene, and aminonitroacetylene. The properties computed were the molecular electrostatic potentials and the bond orders, used as measures of relative bond strengths. Among the interesting structural features found for these molecules are a slight nonlinearity of the mono- and dinitrosoacetylene and the fact that the two substituents in dinitro- and dinitrosoacetylene are not coplanar but rather lie in perpendicular planes. The presence of nitrile is observed to strengthen the carbon triple bond carbon, whereas nitrous oxide substitution weakens it. The combination of nitrogen dioxide and NH2 (a strong electron donor) has an overall weakening effect, relative to acetylene. The carbon nitrogen dioxide bonds are found to be stronger than the nitrile bonds. The electrostatic potential analyses show that the introduction of NO2 completely eliminates the negative regions associated with the triple bond, thus rendering it less susceptible to electrophilic attack. There are found to be buildups of positive potential above the C-NO bonds, indicating that these can serve as initial sites for nucleophilic attack.

Electrostatic potentials and relative bond strengths of some nitro- and nitrosoacetylene derivatives

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectrostatic potentials and relative bond strengths of some nitro- and nitrosoacetylene derivativesPeter Politzer and Ruth Bar-AdonCite this: J. Am. Chem. Soc. 1987, 109, 12, 3529–3534Publication Date (Print):June 1, 1987Publication History Published online1 May 2002Published inissue 1 June 1987https://doi.org/10.1021/ja00246a006RIGHTS & PERMISSIONSArticle Views147Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (657 KB) Get e-Alerts Get e-Alerts

In situ microanalysis for 34S/ 32S ratios using the ion microprobe SHRIMP

The SHRIMP ion microprobe has been used to determine the relative sulfur isotopic compositions of pyrite, pyrrhotite, chalcopyrite, galena, sphalerite, and barite, employing a 10 kV, 3nA, negative oxygen primary ion beam and measuring positive secondary ions accelerated to 11 kV. Tests showed the minerals to be stable emitters of secondary ions, and intensities of the 32S + secondary ion beams ranged from 0.3 to 0.07 MHz in the order: sphalerite > pyrite > chalcopyrite > pyrrhotite > galena > barite, enabling measurement of 34S/ 32S ratios to a precision and accuracy near ±2 permil (2σ). Materials of diverse 34S concentration and/or matrix were repeatedly analyzed without detectable memory effect. Isotopic fractionation during analysis was mineral species-dependent and linear in terms of 32S, 33S, and 34S over a range in delta values of 60 permil, producing easily corrigible ratios and eliminating the need for standards isotopically similar to the samples. Fractionation varied from 1.5 to 6% u −1 in the order: galena < chalcopyrite < pyrrhotite = pyrite < barite and follows the relative bond strengths of the minerals. This apparently simple fractionation behavior suggests that, ultimately, it may be possible to reference all analyses to a single standard. Some irregularity in the fractionation of ratios from sphalerite, possibly related to matrix effects, has delayed its incorporation into this scheme.

Icosahedral C60: an aromatic molecule with a vanishingly small ring current magnetic susceptibility

Smalley and co-workers1 have speculated that an icosahedral C60 molecule might have unusual magnetic properties. Here we report that the π-electron ring-current susceptibility of C60 is unusually small and sensitively dependent on the relative strengths of the two inequivalent bonds of the molecule. For equal bond strengths the susceptibility is only -0.21 that of benzene (with field normal to the plane of the six-membered ring). A 2% change in relative bond strengths is enough to change the sign of the susceptibility with the result that C60 is probably weakly diamagnetic. The shielding effect of the π-electrons is calculated to be less than 1 p.p.m. for an atom placed at the centre of C60. A larger effect is expected for C606-, which is calculated to be strongly diamagnetic.

Groove adhesion test for electrodeposited chromium

A quantitative test has been devised to evaluate the adhesion of electrodeposited chromium on steel substrates. The test involves the cutting of parallel grooves across a plated surface using a small metal shaper equipped with a carbide tool. The grooves are cut at a depth just below the interface and shearing stresses are generated which can produce failure of the coating. In general, varying amounts of residual chromium are left on the surface of the lands depending on the relative cohesive and adhesive bond strengths of the electrodeposited chromium. Energy dispersive x‐ray analysis is used to map the distribution of residual chromium and obtain an intensity count. The ratio of count intensity normalized against a reference of 100% chromium coverage provides a quantitative measurement of adhesion. The groove adhesion test was found to be equally applicable for the evaluation of both hard chromium and soft chromium deposits.

Hydrogen bonding and specificity. Fluorodeoxy sugars as probes of hydrogen bonding in the glycogen phosphorylase-glucose complex.

The affinities of a large number of deoxy and fluorodeoxy sugars for the glucose binding site in glycogen phosphorylase have been measured, and polarities and relative strengths of the hydrogen bonds at each position have been predicted on the basis of these data. Comparison with the recently refined X-ray crystal structure of the phosphorylase-glucose complex shows a generally good correlation between predicted and observed bond strengths, vindicating this approach to the evaluation of hydrogen bonding. Estimates of the net contributions of hydrogen bonds of different types (neutral-neutral and neutral-charged) are essentially identical with those obtained by a complementary approach on the tyrosyl tRNA synthetase-substrate complex [Fersht, A. R., Shi, J. P., Knill-Jones, J., Lowe, D. M., Wilkinson, A. J., Blow, D. M., Brick, P., Cortes, P., Waye, M. M. Y., & Winter, G. (1985) Nature (London) 314, 235-238]. The carbohydrate binding site structure determined is compared with that recently determined for the arabinose binding protein.

Bond-order-bond-energy correlations

A practical procedure for determining the relative strengths of chemical bonds is presented. It is shown, for diatomic and polyatomic molecules, that bond strengths correlate directly with bond orders calculated from force constants and bond lengths. The latter two properties can be obtained either experimentally or computationally.

Plasma Emission Spectroscopy and Chemical Analysis of Amorphous Hydrogenated Carbon

AbstractThe emission spectra of various hydrocarbon plasmas used in the growth of amorphous hydrogenated carbon (α-C:H) thin films have been measured.The presence of CH, H, H2, and C2 species in the plasma have been observed.The chemical composition of the α-C:H films was determined by combustion analysis and shows roughly equal atomic concentrations of H and C and a surprising large concentration of 0.The plasma emission spectra and chemical composition results can be partially understood in terms of relative bond strengths of the different molecules involved, and these results give some insights into the growth kinetics of α-C:H thin films.

On predicting free radical polymerizability of allyl monomers. MINDO/3 and 13C NMR results

AbstractTwo new methods of predicting free radical polymerizability of allyl monomers have been developed. MINDO/3 calculations of eigenvalues for the C—H bond a to the atlyl substituent allow comparison of relative bond strengths. Monomers known to undergo degradative chain transfer display more positive eigenvalues correlating with weaker α‐C—H bonds. Polymerizable monomers have more negative eigenvalues and stronger α‐C—H bonds. The latter possess strongly polarized or protonated substituents not capable of resonance stabilization of a chain‐terminating allyl radical. The inductive effect of such substituents on the 13C NMR peaks of the vinyl carbons is the basis for the empirical spectroscopic method. Allyl compounds display β‐carbon peaks farther downfield than the γ‐carbon peaks. Polymerizable monomers generally have β peaks shifted upfield and γ peaks shifted downfield from those of poor monomers. This effect brings the two peaks closer together in the spectrum. Thus, the smaller the Δδ value (δβ − δγ), the more likely the monomer is to polymerize well. Monomers with intermediate eigenvalues or Δδ values may polymerize with difficulty or only under special conditions. Combined use of the theoretical and empirical techniques can allow prediction of inherent polymerizability and can facilitate evaluation of reaction media most favorable to polymer formation.

ANALYSIS OF BONDING IN CATIONIC CYCLOPENTADIENYLIRON COMPLEXES BY MÖSSBAUER AND INFRARED SPECTROSCOPY

Abstract The σ and π bonding characteristics of acetonitrile, pyridine, ethylene and triphenylphosphine have been studied in several metal environments by combined use of Mossbauer and infrared spectroscopy. Comparisons with earlier studies identify ligand (σ + π) capacities that increase in the order CH3CN < C5H5N ≃ C2H4 < PPh3 < CNMe ≃ C(NHMe)2 < CO. Pyridine is found to be a stronger σ donor than either acetonitrile or ethylene but weaker than triphenylphosphine. Significant π acceptor capacity is evident in both ethylene and triphenylphosphine. Spectroscopic analyses of relative ligand bond strengths are corroborated by the differing tendencies of the complexes in the study to undergo dissociation and disproportionation.

Relative shear bond strengths of luting media with various core materials

T he coronal cast metal restoration continues to be commonly used to restore teeth severely damaged by caries or trauma and to strengthen endodontically treated teeth. Often, however, so little tooth structure remains that a casting could not be adequately supported and retained (either coronally or within the root canal) without an intermediate buildup with a suitable dowel or core. Important factors related to the success of a cast restoration are (1) the ‘design and quality of the tooth or core, and (2) the accuracy of the casting.’ Other factors that contribute to longevity and success include (1) the type of core material to which the casting is cemented, (2) the luting medium and its biophysical characteristics, and (3) the degree of bond strength between the cement and the core material.‘-3 In most instances, the core consists of various combinations of dentin and amalgam alloy, composite resin, noble alloy, or base metal alloy. The bond strength of a luting agent to dentin is an important consideration in the success of the cast restoration. It is equally important that the bond strength of luting agents to various core materials be within the range of clinical acceptability. The bond strengths of various luting agents have been widely reported in the literature, usually presented in terms of tensile characteristics.“’ Fewer studies have dealt with the bond strengths to core materials and dentin in terms of shear strength characteristics.6,7 Both shear and tensile strengths are relevant for retention of a casting. The purpose of this laboratory investigation was to compare the shear bond strength of representative luting agents to materials commonly used as cores for cast restorations.

Local order and structural transitions in amorphous metal-metalloid alloys.

The NiBoPUl alloy system has been investigated in both liquid and amorphous solid forms using molecular-dynamics computer simulation. Atomic interactions were modeled by central pair potentials selected to represent roughly the atomic sizes and relative bond strengths. Self-diffusion constants and pair-correlation functions have been determined as a function of temperature. By means of a mass-weighted steepest descent on the potential-energy hypersurface, dynamical configurations at various temperatures have been mapped onto nearby potential-energy minima (stable atomic packings). This establishes that the liquid phase for the alloy has a temperature-independent inherent structure. Comparison with diffraction data on real Ni-P alloys suggests (and we verify) that improved molecular-dynamics modeling is possible.

Bioadhesive intraoral release systems: design, testing and analysis

The aim of this study was to analyse the adhesion of various polymeric formulations and to measure the in vitro release of a local anaesthetic (febuverine hydrochloride) from a Hydrophobic gel containing 34% (wt/wt) adhesive hydrocolloids. The bioadhesive polymer system was prepared from a polyethylene gel containing various amounts of sodium carfaoxymethylcellulose (NaCMC) as the adhesive, and hydrolysed gelatin as the water sensitive material to ensure rapid swelling. Upon hydration, adhesion studies were performed with a tensile tester equipped with a custom-made cell. The controlled release of the active ingredient was studied with a dissolution cell filled with artificial saliva at 37°C. It was found that the relative adhesive bond strength of the formulations was dependent on the NaCMC content showing a maximum at about 20 wt %. Febuverine hydrochloride release achieved an optimal release rate for formulations with NaCMC in the range of 12–25 wt%.

Correlation of spectroscopic parameters with ligand basicity for uranyl bis(hexafluoroacetylacetonate) adducts

The infrared transition frequencies (vapor and solution phases) of the uranyl and hexafluoroacetylacetonate (hfacac) moieties, as well as /sup 13/C and /sup 1/H NMR shifts, correlate linearly with the relative basicity of the neutral bases (B) for 15 UO/sub 2/(hfacac)/sub 2/ adducts. Solvation effects and relative entropy changes appear to be minimal for the base-exchange equilibrium, suggesting that the observed shifts in thes easily measurable spectroscopic properties predominantly reflect the Lewis acid-base relative bond strengths. We interpret the observed shifts in terms of electronic structure perturbations of both the uranyl and hfacac moieties arising from changes in neutral base (L-M) bonding. 6 figures, 2 tables.

ChemInform Abstract: CHARGE‐OVERLAP STUDY OF MULTIPLE METAL‐METAL BONDING AND CONJUGATION IN LINEAR CHAINS OF TRANSITION‐METAL ATOMS

For a comparative study of bonding, the dsp excited configuration, pertinent to linear digonal hybrids, was imposed on metals of three transition series. Computations of u, r, and 6 overlap of the s, p, and d orbitals in this configuration were made for selected metals, at the usual metallic distance, the distance in A3B superconducting alloys, and the distance for known multiple metal bonds in complexes. The computation made use of single-{ Slater orbitals derived from the same Burns rule for all. Subsequently, molecular orbital calculation of o, r, and 6 bonding for a repeating unit, -(M2)in an infinite chain was made by using an extended Hiickel method and the Mulliken-Wolfsberg and Helmholz approximation. The (same) parameter, K = 1.75, used for all metals was first tested for N2 and P2. The bond stabilization relative to the ground-state atoms, proportional to overlap, was used to approximate the bond dissociation energy. A new attempt was made to justify and to delineate the approximation involved and to show that the neglected two-electron integrals as well as the nuclear repulsion tend to cancel. Coulomb integrals were approximated by valence-orbital ionization energies (VOWS), which for self-consistency were all obtained from existing z-series expansion of the Hartree-Fock SCF energies of the atoms and their ions of appropriate configuration. The dsp configuration energies were also obtained from the same HF-SCF calculations. In cases where data were not available and for the third series the dnsp energies were obtained from weighted averages of spectroscopic term energies given by Moore. Overlap data here support dp hybridization assisted by sp in bonding that is principally do plus d r and d6. The bond strength as well as bond order for a chain peaks at group 6, drops at the first column of group 7, and rises again at group 8. The relative bond strength for do vs. d r vs. d6 bonds was estimated by the ratio of relative stabilizations. Pictures of conjugate bonds and their resonance in a chain, consistent with the translational symmetry of the repeating unit, -(M2)-, and with the conservation of azimuthal angular momentum were drawn. The study suggests that, for a chain of neutral transition-metal atoms, the most favorable multiple bonding occurs for group 5 and group 6 elements (more so for the second series than for the first), the largest number of resonance-conjugation hybrids exists for group 5, and the highest bond order occurs for group 6 atoms.

Application of INEPT 109Ag and 15N NMR Spectroscopy for the study of metal-ligand interactions of silver analogues of copper(I) model compounds

Because of the presence of copper (in its reduced state) at active sites in protein it has become very ▪ important to study copper(I) model complexes by spectroscopic techniques. We now report that if copper(I) in model complexes can be substituted by silver(I) with retention of the structural features then 107Ag or 109Ag NMR spectroscopy (natural abundances 50% I = 1 2 ) using the recently developed polarization transfer sequence INEPT (Insensitive Nuclei Enhanced by Polarization Transfer) [1] provides an excellent tool for studying the metal IB-ligand interaction 1H NMR studies show that the analogous copper(I) and silver(I) complexes of potentially quadridentate N 4 ( R)( S)-1,2-(6-R-pyridine-2-CHN) 2-cyclohexane (R = H or Me) as well as the N 2S 2 donor ligand ( R)( S)-1,2-(5-R-thiophene-2-CHN) 2-cyclohexane (R = H or Me) have similar structures (confirmed by X-ray studies [2]). However, study of the direct coordination sphere and copper(I)-ligand interactions in these model complexes by Cu NMR is hampered by the large quadropole moments of both 63Cu and 65Cu (natural abudances 70 and 30% respectively, I = 3 2 ). We have measured directly 109Ag NMR (INEPT) spectra with large enhancements in signal to noise and enormous experimental time saving (a factor 400–500) as compared to the conventional methods (see Fig. 1) [3]. the influence of the nature of the hetero-atoms coordinating the metal centre is directly reflected in the chemical shift differences of the 109Ag resonances. It is shown that for silver(I) coordination complexes information about the ligand-to-metal interaction can be obtained by using not only direct 109Ag NMR, but also INEPT 15N NMR spectroscopy. In particular the 15N NMR (INEPT) spectra of the silver(I) complexes [M 2(N 4) 2] 2+ 2O 3SCF − 3 show that the structure of these complexes as found in the solid by X-ray methods, in which each metal ion has a distorted tetrahedral coordination geometry of four N-atoms, is fully retained in solution. From different 1J( 15N 107,109Ag) coupling constants the relative bond strengths of the various AgN interactions can be deduced. Where Cu I can be substituted by Ag I either in coordination (model) complexes or biological systems (bovine superoxide dismutase [4]) INEPT 109Ag NMR spectroscopy has potential as a novel technique for the study of the coordinating properties of the metal centres.

Reversible substitution reactions of tetrahedral tetrahaloferrates(III) with thiocyanate

The kinetics substitution of the reversible reactions of SCN −, Cl − and Br − ligands at tetrahedral tetrahaloferrates(III) were studied photometrically in dichloromethane. Infrared spectra show thiocyanate to be N-bonded in these complexes. With the aid of conductometrically-determined ion-pair association constants, evidence was found for an ion-pair, ion-pair mechanism. The activation parameters (ΔH ≠ between 3 and 30 kJ mol −1, ΔS≠ between −77 and −155 J K −1 mol t-1) indicate an associative mode of activation. A linear enthalpy relationship was found (slope 0.57), implying substantial bond-breaking and bond-making in the transition stare (I a mechanism). The relative bond strengths of the (FeX 3)Y − combinations, with X − = Cl − or Br − and Y − = Br −, Cl − or NCS −, vary in the order Br − < Cl − ⪡ NCS −.

Charge-overlap study of multiple metal-metal bonding and conjugation in linear chains of transition-metal atoms

For a comparative study of bonding, the dsp excited configuration, pertinent to linear digonal hybrids, was imposed on metals of three transition series. Computations of u, r, and 6 overlap of the s, p, and d orbitals in this configuration were made for selected metals, at the usual metallic distance, the distance in A3B superconducting alloys, and the distance for known multiple metal bonds in complexes. The computation made use of single-{ Slater orbitals derived from the same Burns rule for all. Subsequently, molecular orbital calculation of o, r, and 6 bonding for a repeating unit, -(M2)in an infinite chain was made by using an extended Hiickel method and the Mulliken-Wolfsberg and Helmholz approximation. The (same) parameter, K = 1.75, used for all metals was first tested for N2 and P2. The bond stabilization relative to the ground-state atoms, proportional to overlap, was used to approximate the bond dissociation energy. A new attempt was made to justify and to delineate the approximation involved and to show that the neglected two-electron integrals as well as the nuclear repulsion tend to cancel. Coulomb integrals were approximated by valence-orbital ionization energies (VOWS), which for self-consistency were all obtained from existing z-series expansion of the Hartree-Fock SCF energies of the atoms and their ions of appropriate configuration. The dsp configuration energies were also obtained from the same HF-SCF calculations. In cases where data were not available and for the third series the dnsp energies were obtained from weighted averages of spectroscopic term energies given by Moore. Overlap data here support dp hybridization assisted by sp in bonding that is principally do plus d r and d6. The bond strength as well as bond order for a chain peaks at group 6, drops at the first column of group 7, and rises again at group 8. The relative bond strength for do vs. d r vs. d6 bonds was estimated by the ratio of relative stabilizations. Pictures of conjugate bonds and their resonance in a chain, consistent with the translational symmetry of the repeating unit, -(M2)-, and with the conservation of azimuthal angular momentum were drawn. The study suggests that, for a chain of neutral transition-metal atoms, the most favorable multiple bonding occurs for group 5 and group 6 elements (more so for the second series than for the first), the largest number of resonance-conjugation hybrids exists for group 5, and the highest bond order occurs for group 6 atoms.