Electronegativity Effects Research Articles

Studies on tautomeric stability and equilibrium of 5(4)-substituted-1,2,3 triazoles. I. Electronegativity and resonance effects of substituent

We have studied the 1,2,3-triazole system with a set of 25 substituents of different electronic features using several methods. Our aim is to find out a calculation method for the analysis of these molecules in biological systems. The combined AIM and NBO study permitted us to justify the observed tautomeric preferences. The absolute predominance of the 2H-tautomer forms is greatly changed when the substituent group possesses anionic character; therefore the pH of the medium is relevant. When the calculations were carried out in solution, noteworthy changes in the behavior of charged substituents were observed. These facts may be relevant when studying the interactions of these molecules with biological receptors.

Identification of an Alcohol with 13C NMR Spectroscopy

The identification of an unknown alcohol with 13C NMR is used to introduce students to NMR spectroscopy early in the second-year undergraduate organic chemistry course. Students learn basic concepts of NMR, including an introduction to magnetic resonance and chemical shifts due to electronegativity effects. This experiment also reinforces knowledge from the lecture on organic molecular structures, including functional groups, isomerization, hybridization, and electronegativity. To identify an unknown alcohol, students obtain the boiling point and perform hands-on 13C and DEPT 90 and 135 experiments with a high-field NMR instrument.

Novel ONN pincer type copper(II) hydrazide complexes: An investigation on the effect of electronegativity and ring size of heterocyclic hydrazides towards nucleic acid/protein binding, free radical scavenging and cytotoxicity

Four new, pincer type copper complexes 5–8 were synthesised from the reactions of CuCl2·2H2O with respective hydrazide ligands 1–4 (HL1–HL4) and characterized by various physicochemical techniques. The single crystal XRD and spectral data revealed that all the ligands are monoanionic, tridentate pincer analogues chelating agent, which coordinate via ONN donor atoms to the copper ion. The effect of electronegativity and ring size of heterocyclic hydrazide moiety of ONN pincer type copper(II) chelates on nucleic acid interaction and protein binding was investigated by in vitro experiments. In addition, scavenging activity and cytotoxicity of the newly synthesized complexes of the composition [Cu(L1–4)Cl] were also evaluated.

Understanding the Unconventional Effects of Halogenation on the Luminescent Properties of Oligo(Phenylene Vinylene) Molecules

It is commonly known that halogenation tends to decrease the luminescence quantum yield of an organic dye, owing to the high electronegativity and heavy-atom effect of the halogen atom. However, based on an investigation of the effects of halogenation on the luminescence of the oligo(phenylene vinylene) (OPV) framework, we demonstrate that halogenation can have positive impact on the solid-state fluorescence and electrochemiluminescence (ECL) properties of OPV derivatives. The chlorinated OPV exhibits a very high solid-state fluorescence quantum yield (91%), whilst the brominated analogue gives the highest ECL emission intensity. Time-dependent density functional theory calculations, natural bond orbital analysis, and natural transition orbital analysis were performed to assist the understanding of the origin of these positive halogenation effects, which provide insight into the rational design of highly luminescent halogenated organic materials for solid-state devices and ECL applications.

Significant Enhancement of Sm3+ Photoreduction in Halide Nanophase Precipitated AlF3-Based Glasses Under Femtosecond Laser Irradiation

The electronegativity effect for the efficient photoreduction of Sm3+ to Sm2+ in Br-modified fluoroaluminate glasses was investigated after femtosecond laser (fs) irradiation. Sm2+ luminescence was strongly observed in the higher Br-modified samples, and basing on the TEM and DSC measurements, BaBr2 nanophases were precipitated from the glass matrix in the laser focused areas. From the EDS spectra, it was found that Sm3+ can be selectively incorporated into the BaBr2 nanophases. More electrons provided by the nanophase facilitated the Sm3+ reduction in the irradiation process. Since the photoreduction efficiency of Sm3+ in Br-modified glass is evidently higher than that in Cl-modified glasses, the effect of halide ions electronegativity on Sm3+ photoreduction was identified and relevant mechanism was discussed.

In-Silico Analysis of Chromone Containing Sulfonamide Derivatives as Human Carbonic Anhydrase Inhibitors

Computational tools of analysis were used on a set of synthetic chromone containing sulfonamide derivatives for evaluation of their enzyme inhibitory activity against Carbonic Anhydrase (CA) isozymes. GOLD docking software was utilized to dock the compounds against two human Carbonic Anhydrase (hCA) proteins; hCAII and hCA-IX. Differences in conformation and orientation of molecules within hCA-II and hCA-IX binding pockets were studied in detail which revealed that compounds with fluorine at R1 position and phenyl sulfonamide substituent at para position served as potent inhibitors against both proteins due to anomalous chemistry of fluorine atom. It was also noticed that the activity was decreased when sulfonamide moiety was shifted from para to meta position since it dragged the interacting specie of compounds away from Zn metal. Similarly, when substituents were replaced by F > Br > C2H5 > H, the activity declined due to the electronegativity effect. Binding interaction results against CA-IX seemed to be better than CA-II due to large binding cavity, predicting the more potent inhibitory activity against hCA-IX.

Effects of anionic structure on the dissolution of cellulose in ionic liquids revealed by molecular simulation

Although ionic liquids (ILs) have shown promise in the pretreatment of cellulose and lignocellulosic biomass, there is no established rule to guide the rational design of such ILs up to date. In this work, the mixtures of cellulose with a series of ILs having the same cation [C2mim]+ but different anions have been simulated to study the effect of anionic nature on the dissolution of cellulose. It was shown that hydrogen bonds (HBs) were formed between anions of the ILs and hydroxyl protons of cellulose. Cl− anion and O atom of [CH3COO]− and [(CH3O)2PO2]− are better HB acceptors. Furthermore, the effects of electronegativity of HB acceptor atoms, steric effect of alkyl chain length and electron-withdrawing group of the anions on their HB acceptor ability have been investigated. The obtained results are expected to be important for the rational design of novel ILs for efficient dissolution of cellulose.

Effect of p–d hybridization, structural distortion and cation electronegativity on electronic properties of ZnSnX2 (X=P, As, Sb) chalcopyrite semiconductors

Significant effects of p–d hybridization, structural distortion and cation-electro-negativity are found on band gap in ZnSnX2 (X=P, As, Sb). Our study suggests these compounds to be direct band gap semiconductors with band gaps of 1.23, 0.68 and 0.19eV respectively. Lattice constants, tetragonal distortion (η), anion displacement, bond lengths and bulk moduli are calculated by Density Functional Theory based on Tight binding Linear Muffin-Tin orbital method. Our result of structural properties is in good agreement with the available experimental and other theoretical results. Calculated band gaps also agree well with the experimental works within LDA limitation. Unlike other semiconductors in the group II–IV–V2, there is a reduction in the band gap of 0.22, 0.20 and 0.24eV respectively in ZnSnX2 (X=P, As, Sb) due to p–d hybridization. Structural distortion decreases band gap by 0.20, 0.12 and 0.10eV respectively. We find that cation electronegativity effect is responsible for increasing the band gap relative to their binary analogs GaInP2, InGaAs2 and GaInSb2 respectively and increment are 0.13, 0.04 and 0.13eV respectively.

Sky-blue phosphorescent iridium(III) complexes with two substituted 2-phenylpyridine derivatives and one picolinic acid for organic light-emitting diodes

Two sky-blue phosphorescent heteroleptic cyclometalated iridium(III) complexes, bis(2-(2′,4′-difluoro-3′-trifluoromethylphenyl)-4-methylpyridinato-N,C2′)iridium(picolinate) [(dfpmpyCF3)2Ir(pic)] (1) and bis(2-(2′,4′-difluoro-3′-hexylcarbazolephenyl)-4-methylpyridinato-N,C2′)iridium(picolinate) [(dfpmpyh-Cz)2Ir(pic)] (2), were synthesized and characterized. Energy transfer from the carbazol moiety to the iridium core in compound 2 resulted in higher quantum efficiency than with compound 1. The electronegative effect of the –CF3 group on the phenyl ring in the phenylpyridine main ligand resulted in a hypsochromic shift of the emitting spectra in compound 1. In contrast, the sky-blue emission without a red shift in compound 2 indicated a negligible inductive effect of the long chain hexylcarbazole unit on the electronic state of the phenyl ring. The single crystal X-ray structural analysis showed that compound 1 adopts a distorted octahedral geometry around the iridium metal exhibiting cis-C,C′ and trans-N,N′ chelate disposition. An electroluminescent devices using the iridium complexes as a dopant in the emitting layer has been fabricated. The best device performance based on compound 1 demonstrated a maximum luminance (L), external quantum efficiency (EQE), luminance efficiency (LE) and power efficiency (PE) of 5750 cd/m2, 7.53%, 16.86 cd/A and 5.88 lm/W, respectively with Commission Internationale de L'Eclairage (CIE) coordinates of (0.17,0.40).

Thermodynamic optimization and calculation of the YCl3–ACl (A=Li, Na, K, Rb, Cs) phase diagrams

The binary phase diagrams of the YCl3–ACl (A=Li, Na, K, Rb, Cs) systems were studied using the CALPHAD technique and nonlinear mathematical method. The new modified quasi-chemical model in the pair-approximation for short-range ordering was applied to describe the Gibbs energies of the liquid phase in these systems. And the paper created the Artificial Neural Networks (ANN) model to study the interaction coefficients of two ending compounds composing the binary systems which are important for thermodynamic study of multi-elements system. Based on measured phase equilibrium data, a set of thermodynamic functions has been optimized and calculated. The effects of ionic radius, electronegativity and mole fraction of YCl3 on interaction coefficients were investigated in more detail.

Quantifying the Effects of Electronegativity and Ionic Radius on Lanthanide Charge Transfer Energy in Inorganic Crystals

Quantifying the Effects of Electronegativity and Ionic Radius on Lanthanide Charge Transfer Energy in Inorganic Crystals

Solid state vibrational spectroscopy of anhydrous lithium hexafluorophosphate (LiPF6)

Raman and infrared studies of solid anhydrous lithium hexafluorophosphate (LiPF6) have been carried out. The studies were complemented by X-ray powder diffraction (XRD) and Thermogravimetric (TG) analysis techniques. The results indicate that when solid LiPF6 is studied in a strictly anhydrous environment, more consistent thermal stability data can be obtained. TG analysis, using a scan rate of 10°Cmin−1, indicate the onset of thermal decomposition of the anhydrous LiPF6 occurring at about 134.84°C while the partially hydrolysed compound starts at 114.46°C. The Raman spectra of anhydrous MPF6 (M=Li+, Na+ and K+) are best interpreted in terms of a cubic space group Fm3m(Ohs), (ZB=1), giving rise to 21 vibrational modes (A1g(R)+Eg(R)+T1g+T2g(R)+3T1u(1R)+T2u) and as such, LiPF6 may be considered isostructural with NaPF6 and KPF6. Crystal symmetry distortions in the anhydrous LiPF6 give rise additional bands in the Raman spectrum due to T1u infrared active modes and the ν1 (A1g) Raman band appears in the infrared spectrum in violation of the mutual exclusion selection rule for centro-symmetric sites. When these observations are considered, the Raman spectrum of LiPF6 is similar to those of NaPF6 and KPF6, with observations of the expected shifts due to cation size and/or electronegativity effects.

Site occupation behavior of sulfur and phosphorus in NiAl, TiAl and FeAl

The site occupation behavior of sulfur and phosphorus in the binary NiAl, TiAl and FeAl alloys is investigated by first-principles calculations. Using a supercell approach, the enthalpies of formation of vacancies, antisites, and substitutional defects are calculated for the three binary alloys. The distributions of S and P in the three alloys and their dependence on Al composition are investigated based on a thermodynamical model. The predicted existence of the dominant defects agrees well with available experimental results and theoretical results. At 1273 K, P atoms occupy exclusively the Al sites in the three alloys, and S atoms occupy exclusively the Al sites in FeAl alloys. However, the concentration of S atoms occupying Ni (Ti) sites increases and that located at Al sites decreases as the Al content increases in NiAl (TiAl). These results cannot be determined from considering only the effects of atomic size and electronegativity on the site occupations. Instead, these results can be understood in terms of differences between the enthalpies of formation for impurity I occupying different sublattices coupled with the configurational entropy differences.

Regioselectivity of Insertion and Role of the Anionic Ligands in the Ruthenium Alkylidene Catalyzed Cyclopolymerization of 1,6-Heptadiynes

The experimentally observed high α-addition selectivity of 1,6-heptadiynes to modified Grubbs–Hoveyda initiators was elucidated with quantum chemical calculations. For these purposes, the two possible pathways of initiation in the Ru alkylidene triggered cyclopolymerization (CP) of 1,6-heptadiynes, resulting in either five-membered (α insertion) or six-membered (β insertion) repeat units, were treated as a multistep process. The first reaction cascade entails the activation of the precatalyst RuX2(IMesH2)(CH-2-(2-PrO-C6H4)) (1: X = F, Cl, Br, I, CF3COO; IMesH2 = 1,3-dimesitylimidazolin-2-ylidene), reaction with a 1,6-heptadiyne (π-1 complex formation), and further transformation into the first metallacyclobutene (MCB-1) followed by ring opening. The second reaction cascade entails again the formation of a π complex (π-2) through binding of the second alkyne moiety of the 1,6-heptadiyne and further transformation into MCB-2 followed by ring opening of MCB-2. The energies of the transition structures for both MCB-1 and MCB-2 formation (TS-1 and TS-2), which are considered the rate-determining steps in CP, are systematically lower for an α insertion of a monomer than for a β insertion. In addition, the geometrical parameters of the most stable structure of the βπ-2 complex are systematically less favorable for MCB-2 formation than in the case of an απ-2 complex, resulting in very high activation energies for βMCB-2 formation. Finally, the formation of βMCB-2 needs an additional step: namely, the endergonic formation of the intermediate βMCB-2*. Since a halogen exchange to pseudohalides in Grubbs–Hoveyda initiators is required to turn them into active initiators in CP, the effect of electronegativity (EN) of the X ligands on the stability of the π-1 complex was calculated for X = I, Br, Cl, CF3COO, F. There, an increase in EN results in lower energies for the α-insertion-derived π-1 complexes. For α insertion, the barriers to the MCB-1 intermediate formation, i.e. the energies of the transition states (TS-1(α)) for MCB-1 formation, decrease in the order I > Br > Cl > CF3COO < F. All findings are consistent with the experimentally observed preference for α insertion in the cyclopolymerization of 1,6-heptadiynes with modified Grubbs–Hoveyda initiators and with the necessity for using pseudohalide variations of the Grubbs–Hoveyda initiator.

Conformational preference of chlorothioformate species: molecular structure of ethyl chlorothioformate, ClC(O)SCH2CH3, in the solid phase and NBO analysis

The molecular structure of ethyl chlorothioformate, ClC(O)SCH(2)CH(3), has been investigated in the solid phase by X-ray diffraction analysis at low temperature using a miniature zone-melting procedure and IR laser radiation. The crystalline solid consists exclusively of molecules with the synperiplanar conformation with respect to the C=O double bond and the S-C single bond, and gauche orientation of the ethyl group (syn-gauche). These results coincide with previous studies devoted to gas-phase conformational properties. The conformational preference for the ClC(O)SY (Y = Cl, CF(3), CH(3) and CH(2)CH(3)) series of molecules was rationalized using the natural bond orbital (NBO) scheme. It was found that both resonance (mesomeric) and anomeric (hyperconjugation) intermolecular charge-transfer interactions are important for describing the syn ↔ anti equilibrium, also illustrating the effect of electronegativity of the substituent in the conformation preference of the ClC(O)S- moiety. On the basis of the atoms in molecules (AIM) theory, intermolecular interactions have been characterized in the B3LYP/6-31G** periodic boundary electron density.

Electronegativity and resonance parameters from the geometry of monosubstituted benzene rings

Reference values of the structural substituent parameters, SE and SR, measuring the electronegativity and resonance effects, respectively, of functional groups (Campanelli et al. J Phys Chem A 107:6429–6440, 2003) have been determined from the benzene ring geometries of 100 Ph–X species, including different conformations of the same molecule. Geometries have been obtained by quantum chemical calculations at the HF/6-31G*, HF/6-311++G**, and B3LYP/6-311++G** levels of theory. The substituent parameters from HF/6-311++G** calculations are in close agreement with those determined at the HF/6-31G* level. Using the B3LYP density functional yields SE and SR values which—in general—correlate well with the corresponding HF values. Exceptions occur with some charged groups, and, in the case of SE, with a few dipolar groups having very high or low electronegativities. SR values from B3LYP calculations are about 22% smaller than the corresponding HF values. The variations of the benzene ring geometry caused by electronegativity, resonance, and steric effects are illustrated in some detail.

Effect of Group Electronegativity on Electron Transfer in Bis(hydrazine) Radical Cations

The radical cation of 4,10-ditert-butyl-5,9-diisopropyl-4,5,9,10-tetraazatetracyclo[6.2.2.2]-tetradecane (sBI4T(+)), as well as its substituted bis(hydrazine) radical cations, is chosen for the investigation of the electronegativity dependence of its intramolecular electron transfer. To do so, two parameters, reorganization energy and electronic coupling, are calculated with several ab initio approaches. It is found that the electronic couplings decrease with the increase of the group electronegativity while the reorganization energies do not show an explicit dependency. Furthermore, Marcus formula is employed to reveal those effect on the electron transfer rates. The predicted rates of electron transfer generally decrease with increasing group electronegativity, although not monotonically.

Structural variations and electronic substituent effects in phenylcubane derivatives: a quantum chemical study

Electronic substituent effects in 4-substituted 1-phenylcubane derivatives, Ph–C8H6–X, have been investigated from the structural changes caused by the substituent X. The molecular structures of 34 derivatives with charged or dipolar substituents have been determined from quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. Geometrical variations caused by substitution appear both in the cubane framework and in the benzene ring, but the two kinds of changes show no correlation. The rather small changes in the benzene ring geometry are caused by long-range polar effects (field effects), while the larger changes in the cubane cage are controlled primarily by electronegativity effects. A structural parameter measuring the long-range polar effect of the substituent, SFCUB, has been derived from the geometry of the phenyl group acting as a probe. This parameter correlates well with the calculated gas-phase acidities of 4-substituted cubane-1-carboxylic acids, HOOC–C8H6–X, and with other indicators of long-range polar effects obtained from bicyclo[2.2.2]octane derivatives. The correlations can further be improved by introducing a resonance parameter as an additional explanatory variable. This indicates that the electron delocalization resulting from hyperconjugative interactions between substituent and cage modifies the long-range polar effect of the substituent. Strong hyperconjugative interactions between some charged substituents and the cubane cage result in remarkable variations in the cage geometry, superimposed onto those ascribed to electronegativity effects.

ELECTRONEGATIVITY EFFECTS ON THE BANDGAP BOWING CHARACTERS IN COMPOUND-SEMICONDUCTOR TERNARY ALLOYS

We present a theoretical investigation of the existence and origins of the bandgap bowing character in compound semiconductor alloys based on both the sp3s*-tight-binding (TB) method, which includes the spin–orbit coupling, and the first-principle Full-Potential Linear Augmented Plane Wave (FP-LAPW) technique. First, we compare the bandgap variation versus composition in the III–V direct-bandgap- GaAs -based ternary alloys, namely between the common-cation GaSb x As 1-x and the common-anion Ga 1-x In x As ternary alloys. The results show that the bowing behavior exists only in the common-cation (i.e., GaSbAs ) alloys as a result of an existing competition between the anion atoms ( Sb and As ) in trapping the electronic charge. The bowing parameter is found to be proportional to the electronegativity characters of the competing anions (i.e., χanion). The lack of such competition, in the case of common-anion alloys (i.e., GaInAs ), makes the bowing be just absent and the variation of the bandgap become close to linear. Second, we have made a clear contrast in the bowing characters between the common-cation III–V and the common-anion II–V ternary alloys by assessing the effect of anion electronegativity (as example, we consider the GaSb x As 1-x and CdSe x Te 1-x ternary alloys). The results show that the bowing character in the II–VI alloys is stronger than the one of III–V alloys as to be simultaneously proportional to the electronegativity of anions ([Formula: see text]) and to the electronegativity mismatch between them ([Formula: see text]). Finally, the excellent agreement between our theoretical results and recent photoluminescence data has further corroborated our claims.

Modeling of dual frequency capacitively coupled plasma sources utilizing a full-wave Maxwell solver: II. Scaling with pressure, power and electronegativity

The trend in dielectric etching in microelectronics fabrication with capacitively coupled plasmas is the use of multiple frequencies where a high frequency (HF, tens to hundreds of MHz) dominates ionization and a low frequency (LF, a few to tens MHz) is used to control ion energy distributions to the wafer. Process parameters, such as pressure, gas mixture and LF and HF power deposition, are important to determining the uniformity of the plasma and properties of ions incident on the wafer. In this paper, we report on a computational investigation of the consequences of these parameters on uniformity and ion energy distributions to the wafer in a dual frequency capacitively coupled plasma reactor sustained in Ar/CF4 gas mixtures. Due to the coupling of finite wavelength, electromagnetic skin, electrostatic edge and electronegative effects, there are no simple scaling laws for plasma uniformity. The plasma uniformity is ultimately a function of conductivity and energy relaxation distance of electrons accelerated by electric fields in and near the sheath. There is a strong second-order effect on uniformity due to feedback from the electron energy distributions (EEDs) to ionization sources. The trends from our parametric study are correlated with the spatial variation of the HF electric field, to the total power deposition and to the spatial variation of EEDs and ionization sources.