Theoretical study of low‐lying electronic states of the LiRb+ molecular ion: Structure,spectroscopy and transition dipole moments

The electronic structure and the spectroscopic properties for low‐lying electronic states of the LiRb⁺ molecular ion, dissociating into Li (2s, 2p, 3s, 3p, 3d, 4s, and 4p) + Rb⁺ and Li⁺ + Rb (5s, 5p, 4d, 6s, 6p, 5d, and 7s), have been investigated using an ab initio approach based on non‐empirical pseudo potentials for the Li and Rb cores and parametrized l‐dependent polarization potential. We have determined the adiabatic potential energy curves and their spectroscopic constants for many electronic states of ²Σ⁺, ²Π, and ²Δ symmetries. A satisfying agreement, for the spectroscopic constants, has been obtained for the ground and the first excited states with the available theoretical works. Potential energy curves were presented, for the first time, for the higher excited states. In addition, we have localised and analysed the avoided crossings between electronic states of ²Σ⁺ and ²Π symmetries. Their existences can be related to the interaction between the potential energy curves and to the charge transfer process between the two ionic systems Li⁺Rb and LiRb⁺. Moreover, we have determined the transition dipole moments from X²Σ⁺ and 2²Σ⁺ states to higher excited states of ²Σ⁺ and ²Π symmetries. For our best knowledge, no experimental data on the LiRb⁺ molecular ion is available. These theoretical data can help experimentalists to optimize photoassociative formation of ultracold LiRb⁺ molecular ion and their longevity in a trap or in an optical lattice. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

The ionization constants of 2‐substituted 4,6‐diamino‐s‐triazines: The applicability to the hammett and taft equations

The ionization (or basicity) constants (pK_b) were determined for many 2‐substituted 4,6‐diamino‐s‐tri‐azines ( I ) by means of the electrometric titration. I includes 2‐alkoxy or aryloxy‐( Ia ), 2‐alkyl‐ or 2‐aryl‐( Ib ), and 2‐alkylamino‐ or 2‐arylamino‐4,6‐diamino‐s‐triazines ( Ic ). For the series with the same alkyl or aryl group, the order of the basicity was found to be Ic < Ib < Ia . A study was made of relationships between the pK_b, values of I , and the substituent constants, σ_p, σ_m, σ_p⁺, σ_m⁺, σ_p^O, σ_m^o, σ_I, σⁿ, and σ*. The Hammett relationships were observed between the pK_a values of I, and the substituent constants σ_m, (or the combination ones, [0.97σ_m + 0.03σ_p] as well as another [0.77σ_I + 0.23σ_R]). The Taft relationships were also found between the pK_a values of Ia , Ib , and Ic and the constants σ_*, respectively. Furthermore, in the case of Ic a linear relationship was observed between the pK_a values and Σσ⁸.     

Synthesis and characterization of the new 22-π aromatic furan-containing macrocycle, “ozaphyrin”

The new 22-π, aromatic “pentaplanar” macrocycle, ozaphyrin ( 6 ), has been synthesized by a McMurry coupling of 5,5′-diformyl-4,4′-dipropyl-2,2′-bipyrrole ( 1 ) with 2,5-bis(5-formyl-4-propyl-2-pyrrolyl)furan ( 5 ). This synthetic pathway to ozaphyrin and its characterization by ¹H nmr spectroscopy, uv-visible spectroscopy, cyclic voltammetry, and X-ray crystallography are described. The structure consists of layers of planar, staggered macrocycles stacked perpendicular to the α-axis. Ozaphyrin crystallizes with four formula units in the monoclinic space group C⁵_2h-P2₁/n in a cell of dimensions a = 10.481(7) Å, b = 17.353(17) Å, c = 18.726(12) Å, and β = 102.84(5)° (108 K). The structure has been refined on F² (5171 unique reflections, 411 variables) to R_w(F_o²) = 0.165. The conventional agreement index R(F) is 0.074 for the 3289 reflections have F_o²>2o(F_o²).     

Substitution électrophile aromatique dans l'anhydride sulfureux liquide. Influence de la concentration en bromure et rôle du solvant sur la réactivité des anisoles au cours de la réaction de bromation

Electrophilic Aromatic Substitution in Liquid Sulfur Dioxide. Kinetic Dependance of Rate on the Bromide Concentration and Influence of the Solvent during the Course of the Reaction On the reported data for bromination of anisole and eleven of its derivatives in liquid SO₂, it was shown that, with a large excess of bromide, the rate of reaction, obeys a first-order law. Rate constants thus obtained do not discriminate between the two different forms of bromide, e.g. Br₂ and Br^?₃ present as the A⁺Br^?₃ form, and corrections were made by use of the apparent equilibrium constant K′ for tribromide formation. The variations of rate constants with initial concentration of bromide has been studied and the effect results in a retardation of the bromination rate. Moreover, the ratio [Br₂] [A⁺Br^?]_T, which is constant during an experiment, varies with initial bromide concentrations, this variation affecting the total rate. To account for the bromide effect on the reactivity, variations of k^o,p_g {1 + K′[A⁺Br^?]_T}VS[A⁺Br^?]_T were studied over a 0.01 to 1M range of bromide concentration. The mechanism proposed shows that liquid SO₂ helps the reactive intermediate to be deprotonated and because of solvation of reactive species this step would probably be rate determining. Bromination by molecular bromine is more sensitive to substituent effects in liquid SO₂ than in water. This result is ascribed to the +M effect of the methoxy group which increase the conjugation of ortho-substituted derivatives (p⁺_p = ?7.83; p⁺_o= ?10.47).     

Zur Kenntnis des chinoiden Zustandes—XVI. Massenspektrometrische untersuchungen an chinonen,diphenochinonen und stilbenchinonen

Besides o-benzoquinones and o-naphthoquinones, p-quinones and stilbene quinones also exhibit [M + 2]⁺·-peaks. These are mainly produced by the residual moisture in the mass spectrometer and are more dependent on the partial pressure of the compounds and of the present water respectively, than on the temperature. The spectra of the [M + 2]⁺·-ions correspond to those of the ionized quinols. There exists a parallelism between the redox potential and the intensity of the [M + 2]⁺·-peak of p-quinonoid systems. The electron-impact induced fragmentations of 2,6-ditert.-butyl-benzoquinone-(1,4) and 3,5-di-tert.-butylbenzoquinone-(1,2) are discussed.     

Kinetic investigation of gas‐phase reactions between the OH‐radical and o‐, m‐, p‐ethyltoluene and n‐nonane in air

We have carried out relative rate experiments (T = 294 ± 2 K, atmospheric pressure) to investigate the OH‐oxidation of o‐, m‐, and p‐ethyltoluene and n‐nonane (k₁, k₂, k₃, and k₄ respectively). The experiments were performed in a 2‐m³ smog chamber with Teflon coated walls. The rate constants obtained are (in cm³ molecule^?1 s^?1 with two sigma uncertainties): k₁ = (1.36 ± 0.07) × 10^?11; k₂ = (2.12 ± 0.26) × 10^?11; k₃ = (1.47 ± 0.04) × 10^?11, and k₄ = (0.95 ± 0.02) × 10^?11. The measured rate constants are in accordance with previously published data, so that a coherent group of values for the compounds studied can be established. Atmospheric implications, ozone, and particle production are discussed. In addition, we have determined the amount of o‐, m‐, and p‐ethyltoluenes in different types of gasoline. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 367–378 2004     

Synthesis of novel 5‐aryl‐1H‐tetrazoles

In this study phenylselenocyanate and some of its derivatives (o‐Cl, p‐Cl, p‐Br, o‐NO₂, p‐NO₂, o‐CH₃, p‐CH₃, o‐COOH, p‐COOH, p‐OCH₃ substituted) were synthesized ( 3a–3j ). The synthesized compounds were converted to 5‐aryl‐1H‐tetrazole ( 4a–4j ), by Et₃N ċ HCl‐NaN₃ in toluene, which are a new series of phenylselanyl‐1H‐tetrazoles. The structure of all the presently synthesized compounds were confirmed using spectroscopic methods (FTIR, ¹H NMR, MS). © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:255–258, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20293     

Kinetics of oxidation of pantothenic acid by chloramine‐T in perchloric acid and in alkaline medium catalyzed by OsO4: A mechanistic approach

Kinetics of oxidation of pantothenic acid (PA) by sodium N‐chloro‐p‐toluenesulfonamide or chloramine‐T (CAT) in the presence of HClO₄ and NaOH (catalyzed by OsO₄) has been investigated at 313 K. The stoichiometry and oxidation products are same in both media; however, their kinetic patterns were found to be different. In acid medium, the rate shows first‐order dependence on [CAT]_o, fractional‐order dependence on [PA]_o, and inverse fractional‐order on [H⁺]. In alkaline medium, the rate shows first‐order dependence each on [CAT]_o and [PA]_o and fractional‐order dependence on each of [OH^?] and [OsO₄]. Effects of added p‐toluenesulfonamide and halide ions, varying ionic strength, and dielectric constant of medium as well as solvent isotope on the rate of reaction have been investigated. Activation parameters were evaluated, and the reaction constants involved in the mechanisms have been computed. The proposed mechanisms and the derived rate laws are consistent with the observed kinetics. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 201–210, 2005     

Composition of the gas phase over Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and the enthalpies of atomization of AlO,Al<Subscript>2</Subscript>O,and Al<Subscript>2</Subscript>O<Subscript>2</Subscript>

The A1, O, AlO, A1₂O, Al₂O₂, WO₂, and WO₃, partial pressures in the vapor over Al₂O₃ in a tungsten Knudsen effusion cell between 2300 and 2600 K were derived from A1⁺, O⁺, AlO⁺, A1₂O⁺, Al₂O₂⁺, WO₂⁺, and WO₃⁺, ion intensities. The mass spectrometer was calibrated against the equilibrium constant of the WO₃(g) = WO₂(g) + O(g) reaction. Refined values of the ionization cross sections of AlO and A1₂O₂ were used in the partial pressure calculations. The enthalpies of atomization of aluminum suboxides were determined to be Δ_at H ^o(AlO, g, 0) = 510.7 ± 3.3 kJ mol⁻¹, Δ_at H ^o(Al₂O, g, 0) = 1067.2 ± 6.9 kJ mol⁻¹, and Δ_at H ^o(Al₂O₂, g, 0) = 1556.7 ± 9.9 kJ mol⁻¹.     

Influence of tertiary aromatic diamines on the n-buLi-initiated polymerization of isoprene in hexane solution

The influence of three aromatic tertiary diamines, bis(4-dimethylamino phenyl) methane (DMAPM), N,N,N′,N′-tetramethyl-p-phenylenediamine (p-TMPDA), and N,N,N′,N′-tetramethyl-o-phenylenediamine (o-TMPDA), on the kinetics of polymerization of isoprene in hexane solution, with n-BuLi as initiator, was studied for different values of ratio r = [amine]/[n-BuLi]. It is shown that added amine increases initiation rate according to its complexing ability (DMAPM < p-TMPDA « o-TMPDA); this result is explained by the formation of complexes between amine A and n-BuLi, (n-BuLi, A)_x, where x = 6, 4, and 1 for the three amines, respectively. The propagation rate and the structure of polyisoprene are modified with o-TMPDA only; the decrease in propagation rate and the increase in 3,4 units in the polymer obtained when r increases are assigned to the formation of solvated ion pairs PI^?Li⁺, o-TMPDA.     

Ion-selective electrodes based on p-tert-butyl-homooxacalixarene di(ethyl)amides

The diethyl amides of p-tert-butyldihomooxacalix[4]arene (1), p-tert-butylhexahomotrioxacalix[3]arene (2) and p-tert-butylcalix[4]arene (3) were used as active materials in ion-selective membrane electrodes to check the detection of different kinds of cations (Na⁺, K⁺, Cs⁺, Mg^2 + , Ca^2 + , Mn^2 + , Cu^2 + , Zn^2 + , Cd^2 + , Pb^2 +  and tetramethylammonium cation). The electrode characteristics and selectivity coefficients were determined and compared. Optimisation of the PVC membrane composition was achieved using three different plasticisers (bis(2-ethylhexyl) adipate, o-nitrophenyl octyl ether and bis(2-butylpentyl) adipate). Amide 3 shows selectivity for Na⁺, whereas compounds 1 and 2 exhibit the highest selectivity for Pb^2 +  among all the studied cations. The X-ray crystal structure of dihomooxacalix[4]arene tetra(diethyl)amide (1) was determined, revealing it to be in the cone conformation.     

Solvent extraction of univalent and bivalent metal picrates with 1,2-bis[2-(2-methoxyethoxy)ethoxy] benzene (noncyclic crown ether) into CHCl3

The overall extraction equilibrium constants, K_ex, of 1:1:m complexes of 1,2-bis[2-(2-methoxyethoxy)ethoxyjbenzene (AC · B18C6) with uni- and bivalent metal picrates, MA _m were determined at 25°C between CHCl₃ and water, and thereby the ion-pair complex-formation constants,K _MLA,o, of AC · B18C6 with the univalent metal picrates in CHCl₃ were calculated. The AC · B18C6 is an open-chain analog of benzo-18-crown-6 (B18C6). The equilibrium constants of AC · B18C6 were compared with those of B18C6. K_ex sequences of AC · B18C6 for uni- and bivalent metals are Tl⁺ > K⁺ > Rb⁺ > Cs⁺ > Na⁺ > Li⁺ and Pb²⁺ > Ba²⁺ > Sr²⁺, respectively. The same extraction-selectivity was observed for B18C6, but the extractability of AC · B18C6 for the same cation is much lower than that of B18C6; the extraction selectivity of AC · B18C6 for alkali metals is lower than that of B18C6. TheK _MLA,o sequence of AC · B18C6 is K⁺ > Rb⁺ > Tl⁺ > Cs⁺ Na⁺, which is consistent with that of B18C6. ButK _MLA,o of AC · B18C6 is much smaller than the correspondingK _MLA,o of B18C6; the selectivity of AC · B18C6 among alkali metal picrates in CHCl₃ is lower than that of BI8C6. This reflects the difference in the structures between AC · B18C6 (acyclic and flexible) and B18C6 (cyclic and rigid).     

Tetraalkylammonium Picrates in the Dichloromethane–Water System: Ion-Pair Formation and Liquid–Liquid Distribution of Free Ions and Ion Pairs

Equilibria concerning picrates of tetraalkylammonium ions (Me₄N⁺, Et₄N⁺, Pr₄N⁺, Bu₄N⁺, Bu₃MeN⁺) in a dichloromethane−water system have been investigated at 25 ^∘C. The 1:1 ion-pair formation constants (K _IP,o ^o) in dichloromethane at infinite dilution were conductometrically determined. The distribution constants (K _D ^o) of the ion pairs and the free cations between the solvents were determined by a batch-extraction method. The K _IP,o ^o value varies in the cation sequence, Bu₄N⁺ ≈ Pr₄N⁺ ≈ Et₄N⁺ < Bu₃MeN⁺ < < Me₄N⁺; this trend is explained by the electrostatic cation−anion interaction taking into account the structures of the ion pairs determined by density functional theory calculations. For the ion pairs of the symmetric R₄N⁺ cations, there is a linear positive relationship between log₁₀ K _D ^o and the number of methylene groups in the cation (N _{CH 2}). The ion pair of asymmetric Bu₃MeN⁺ has a higher distribution constant than that expected from the above log₁₀ K _D ^o versus N _{CH 2} relationship. These cation dependencies of log₁₀ K _D ^o for the ion pairs are explained theoretically by using the Hildebrand-Scatchard equation. For all the cations, the log₁₀ K _D ^o value of the free cation increases linearly with N _{CH 2}; the variation of log₁₀ K _D ^o is discussed by decomposing the distribution constant into the Born-type electrostatic contribution and the non-Born one, and attributed to the latter that is governed by the differences in the molar volumes of the cations. The cation dependencies of the ion-pair extractability and ion pairing in water are also discussed. An erratum to this article can be found at     

Nonaqueous Solution Studies on the Protonation Equilibria of some Phenolic Acids

The protonation equilibria for some phenolic acids in nonaqueous solutions have been studied by pH-potentiometry. The dissociation constants, pK _a, of these phenolic acids and the thermodynamic functions, ΔG ^o,ΔH ^o and ΔS ^o, for the successive and overall protonation processes of these phenolic acids have been derived at different temperatures in three different mixtures of water and dioxane (mole fractions of dioxane were 0.083, 0.174 and 0.33). Titrations were also carried out in (water + dioxane) with ionic strengths of 0.15, 0.20 and 0.25 mol⋅dm⁻³ NaNO₃, and the resulting dissociation constants are reported. A detailed thermodynamic analysis of the effects of organic solvent, dioxane, temperature and ionic strength on the protonation processes of phenolic acids is presented and discussed to determine the factors which control these processes. Ahmed E. Fazary; previous address: Egyptian Organization for Biological Products and Vaccines, 51 Wezaret El-Zeraa Street, Agouza, Giza, Egypt. Tel. +2010-3017357.     

Study of substituted aryldiazonium salts and their crown ethers complexes by XPS

The complexes of fourteen substituted aryldiazonium salts RC₆H₄N₂+BF₄^? (R?H, p-CH₃, p-NO₂, p-I, p-Cl, p-F, m-Br, m-Cl. m-CH₃, o-CH₃, o-OCH₃, o-NO₂, o-Br, o-Cl) with crown ethers 18-C-6 (1) and dibenzo-24-c-8 (2) have been studied by XPS. The results show that the chemical shifts of α-N1s and β-N1s of substituted aryldiazonium salts are closely related to the induction and conjugation effects of R groups. It is interesting to note that charge transfer(β-N→O) take place upon complexation of substituted aryldiazonium salts with crown ethers. Therefore the decrease of binding energy of crown ether oxygen may be used as a measurement of the stabilities of these complexes.     

Effects of Aromatic Fluorine Substitution on Protonated Neurotransmitters: The Case of 2‐Phenylethylamine

Fluorination of pharmaceutical compounds is a common tool to modulate their physiochemical properties. We determine the effects of site‐specific aromatic fluorine substitution on the geometric, energetic, vibrational, and electronic properties of the protonated neurotransmitter 2‐phenylethylamine (xF‐H⁺PEA, x=ortho, meta, para) by infrared multiphoton photodissociation (IRMPD) in the fingerprint range (600–1750 cm^?1) and quantum chemical calculations at the B3LYP‐D3/aug‐cc‐pVTZ level. The IRMPD spectra of all ions are assigned to their folded gauche conformers stabilized by intramolecular NH⁺???π hydrogen bonds (H‐bonds) between the protonated amino group and the aromatic ring. H→F substitution reduces the symmetry and allows for additional NH⁺???F interactions in oF‐H⁺PEA, leading to three distinct gauche conformers. In comparison to oF‐H⁺PEA, the fluorination effects on the energy landscape (energy ordering and isomerization barriers) in pF‐H⁺PEA and mF‐H⁺PEA with one and two gauche conformers are less pronounced. The strengths of the intramolecular NH⁺???F and NH⁺???π bonds are analyzed by the noncovalent interaction (NCI) method.     

Complexing ability of pesticides and related compounds. Formation and stability in aqueous solution of H+ , Li+, Na+, K+, Mg2+ and Ca2+ phenoxyacetate complexes at different temperatures and ionic strengths

The formation constants of Li⁺, N⁺, K⁺, Mg²⁺ and Ca²⁺ phenoxyacetate complexes were determined potentiometrically using an (H⁺)-glass electrode at 10, 25, 37 and 45°C, at several ionic strengths, in the range 0.04?I? 0.9 mol 1^?1. Simple empirical equations for the dependence of the formation constants on ionic strength were derived. From the temperature coefficients, estimates of ΔH^o and ΔS^o were obtained.     

Darstellung und Strukturdaten von „Delafossiten”︁ CuMO2 (M = Al,Ga, Sc,Y)

Synthesis and Structural Data of “Delafossites” CuMO₂ (M = Al, Ga, Sc, Y) By solid state reaction of their binary components 2H-CuScO₂, R-CuGaO₂, and R-CuYO₂ were synthesized for the first time. Their crystal structures were determined, and those of R-CuAlO₂ and 2H-CuAlO₂ refined. Characteristic structural features (lattice constants and interatomic distances) are discussed with respect to possible Cu⁺? Cu⁺ interactions.     

A Nontrigonal Tricoordinate Phosphorus Ligand Exhibiting Reversible “Nonspectator” L/X‐Switching

We report here a “nonspectator” behavior for an unsupported L ‐function σ³‐P ligand (i.e. P{N[o‐NMe‐C₆H₄]₂}, 1a ) in complex with the cyclopentadienyliron dicarbonyl cation (Fp⁺). Treatment of 1a ?Fp⁺ with [(Me₂N)₃S][Me₃SiF₂] results in fluoride addition to the P‐center, giving the isolable crystalline fluorometallophosphorane 1a^F ?Fp that allows a crystallographic assessment of the variance in the Fe?P bond as a function of P‐coordination number. The nonspectator reactivity of 1a ?Fp⁺ is rationalized on the basis of electronic structure arguments and by comparison to trigonal analogue (Me₂N)₃P?Fp⁺ (i.e. 1b ?Fp⁺), which is inert to fluoride addition. These observations establish a nonspectator L/X‐switching in (σ³‐P)–M complexes by reversible access to higher‐coordinate phosphorus ligand fragments.     

CO<Subscript>2</Subscript> adsorption and dehydration behavior of LiNaX,KNaX, CaNaX and CeNaX zeolites

In this study, NaX synthetic zeolite was modified by following the conventional cation exchange method at 70°C. 82, 81, 79 and 48% of sodium were exchanged with Li⁺, K⁺, Ca2⁺ and Ce3⁺, respectively. Thermal analysis data obtained by TG/DSC was used to evaluate the dehydration behavior of the zeolites. The strongest interaction with water and the highest dehydration enthalpy (ΔH) value were found for Li-exchanged form and compared with the other forms. The temperature required for complete dehydration increased with decreasing cation size (cation size: K⁺>Ce³⁺>Ca2⁺>Na⁺>Li⁺). CO₂ adsorption at 5 and 25°C was also studied and the virial model equation was used to analyze the experimental data to calculate the Henry’s law constant, K _o and isosteric heat of adsorption at zero loading Q _st. K _o values decreased with increasing temperature and the highest Qst was obtained for K rich zeolite. It was observed that both dehydration and CO₂ adsorption properties are related to cation introduced into zeolite structure.