Theoretical study of the electronic structure of diazomethane

The least-energy dissociation path of the ground state of CH₂N₂ was determined fromab initio calculations using in a complementary way basis sets of minimal size (STO-3G) and double-zeta (DZ) quality. The results indicate that the least-energy point of attack of the N₂ molecule on CH₂ (¹ A ₁) is roughly perpendicular to the molecular plane (93 °), the C and N atoms being almost co-linear (angle C-N-N203 ° with outermost N atom pointing away from CH₂). The potential barrier of 1.2 eV found previously on theC _2v dissociation path, disappears completely along the least-energy dissociation path (point groupC _s (out-of-plane)). These findings corroborate the Woodward-Hoffman rules for this process since the outermost orbitals of the two intersecting states found in point groupC _2v (...2b ₁ and ...8a ₁) both correlate to the same irreducible representation (10á) in point groupC _s (out-of-plane).Larger basis set calculations (DZ + polarization functions on all centers, 3d _c and 3d _N developed here), were also carried out on CH₂N₂ (¹ A ₁,³ A ₂ and¹ A ₂) at the¹ A ₁ equilibrium geometry and on CH₂ (³ B ₁) and N₂ (¹ _g ⁺ ) at their respective equilibrium geometries. These calculations, together with consideration of correlation energy differences, yieldD ₀ ⁰ (CH₂N₂,¹ A ₁) = 19 kcal/mole and vertical excitation energies of 67 and 73 kcal/mole for the³ A ₂ and¹ A ₂ states respectively. The latter value is in good agreement with the measured experimental value: 72.4 kcal/mole corresponding to the maximum of intensity in the¹ A ₂¹ A ₁ absorption band.     

Dissociation of diimide

Parts of the potential energy surface of N₂H₂ have been studied using CASSCF- and contracted CI-methods. Of particular interest was the concerted dissociation of cis- and trans-diimide into N₂ and H₂, since the trans-dissociation is symmetry allowed and the cis-dissociation forbidden. Three different saddle points were located, of which only one, of C ₂- symmetry, is a true transition state. Elaborate numerical gradient methods using exact Hessians and update procedures had to be used to find these saddle points on the unexpectedly complex N₂H₂-surface. The barrier height with respect to trans-diimide is 61 kcal/mol after vibration correction. Since this energy is higher than the barrier for interconversion, cis- and trans-diimide have the same transition state. It is further found that diimide preferably dissociates stepwise, by losing one hydrogen at a time, rather than in a concerted way. This conclusion is drawn basically because the geometry of the transition state for the concerted dissociation has a very long H-H distance of 5.6 a.u. The N-H bond energy in trans-diimide is 56 kcal/mol after vibration correction.     

Quantum chemical studies on electrophilic addition

The geometries of the 2-hydroxyethyl and isomeric oxiranium cations have been fully optimized using ab initio molecular orbital calculations employing the split valence shell 4-31G basis set. These species are possible intermediates in both the electrophilic addition of OH to ethylene and in the acid catalysed ring opening of oxirane. The optimized structures were then used to compute more accurate wave functions using Dunning's double-zeta basis set, and with this large basis set the bridged oxiranium ion was found to be the more stable by 7.2 kcal/mole. The barrier to interconversion of these two C₂H₄OH ions was computed to be 25.0 kcal/mole above the oxiranium ion.     

Quantum chemical studies on electrophilic addition

The geometries of the 2-aminoethyl cation and the isomeric protonated aziridine have been optimized using ab initio molecular orbital calculations employing the split-valence shell 4-31G basis set. The protonated aziridine is computed to be the more stable ion by 46.5 kcal/mole (4-31G level) and 44.9 kcal/mole (double-zeta basis set). The profile to interconversion is found to have a barrier of less than 15 kcal/mole (relative to the 2-aminoethyl cation) and this profile is compared with those computed for the similar ions XCH₂CH ₂ ⁺ where X=OH, F, SH and Cl.     

The determination of enthalpies of formation of organic free radicals from bond dissociation energies. 5. Organosulfur radicals

The formation enthalpies (H _f°) of 12 organosulfur radicals (R^·) were determined for the first time from the published values of dissociation energies of R—X bonds.     

The electrochemistry of the inclusion complex of anthraquinone withβ-Cyclodextrin studied by means of OSWV

The reduction of anthraquinone (AQ) in the presence of -Cyclodextrin (-CD) has been investigated by Osteryoung square wave voltammetry (OSWV) in phosphate buffer (pH = 7.0). -CD forms a 1 : 1 inclusion complex with AQ. The experimental results show that -CD causes a decrease in the peak current (I _p) and a negative shift in the peak potential (E _p) for AQ reduction. The relationship betweenI _p (andE _p) and the concentration of -CD has been studied. The dissociation constant of the inclusion complex,K _d = 3.5 × 10^–3 mol/L, was obtained from the plot ofI _p ^/2 vs. (I _p ^(AQ)/2 –I _p ^/2 ) [CD]. The diffusion coefficients of free AQ and in the presence of -CD have been determined by means of chronocoulometry (CC). The adsorption properties of -CD on glassy carbon and gold electrodes was investigated. UV vis spectra gave further evidence for complexation and the dissociation constant determined spectroscopically,K _d ^/ = 4.5 × 10^–3 mol/L, was in agreement with that obtained electrochemically.     

Ab initio MP2 calculations of the products of acetylene addition to HgCl2

Gas-phase reaction of acetylene with HgCl₂ resulting in -chlorovinylmercury derivatives and their interaction with Cl^– and I^– anions and KI molecule was studied by the ab initio MP2 method with the Dunning—Hay double zeta basis set and LanL pseudopotential for Hg, K, and I atoms. The reaction was shown to proceed via a -complex of acetylene and HgCl₂ (the calculated enthalpy of formation is –6.5 kcal mol^–1). According to calculations, the activation energy of formation of cis--chlorovinylmercury chloride from acetylene and HgCl₂ is 31 kcal mol^–1. Chloride and iodide anions and KI molecule are readily added to both cis- and trans-isomer of -chlorovinylmercury chloride to give stable species.     

Kinetic studies on the thermal dissociation of the inclusion complex of β-cyclodextrin with cinnamic aldehyde

The stability of the inclusion complex of -CD with cinnamic aldehyde was investigated by means of TG and DSC. The mass loss takes place in three stages: dehydration occurs at 50–120°C; dissociation of -CD·C₉H₈O proceeds in the range 200–260°C; and decomposition of -CD begins at 280°C. The kinetics of the dissociation of -CD·C₉H₈O was studied by means of thermogravimetry both at constant temperature and with linearly increasing temperature. The results demonstrate that the dissociation of -CD·C₉H₈O is dominated by a one-dimensional diffusion process. The activation energyE is 160 kJ mol^–1, and the pre-exponential factorA is 5.8×10¹⁴ min^–1. Scanning electron microscope observations and the results of crystal structure analysis are in good agreement with those of thermogravimetry.     

Solute-solvent effects in the acidic dissociation of the ampholyte N-tris(hydroxymethyl)methylglycine (“tricine”) in 50 mass % methanol-water solvent

The pK values for the two acidic dissociation steps of the ampholyte N-tris-(hydroxymethyl)methylglycine (tricine) in 50 mass % methanol-water solvent have been determined by emf measurements of cells of the type Pt|H₂(g, 1 atm), tricine buffer, Br^–, AgBr|Ag over the range 5 to 50°C (pK ₁)and 5 to 60°C (pK ₂).The standard thermodynamic quantities H^o, S^o, and C _p ^o for the two dissociation processes have been derived and are compared with the corresponding values for tricine and the parent glycine in water and with those for other acids in 50 mass % methanol-water solvent. Both tricine and protonated tricine become weaker acids when methanol is added to the aqueous solvent. It appears that a strong stabilization of the zwitterion in water is responsible for this behavior. This conclusion is supported by comparing the changes in entropy and heat capacity for the dissociation of tricine with the values of these quantities for the dissociation of model acids of simple structure, such as ammonium ion and acetic acid.On leave 1971–1973 from Drury College, Springfield, Missouri     

The rate of the gas phase iodination of cyclobutane. The heat of formation of the cyclobutyl radical

The gas phase iodination of cyclobutane was studied spectrophotometrically in a static system over the temperature range 589° to 662°K. The early stage of the reaction was found to correspond to the general mechanism where the Arrenius parameters describing k₁ are given by log k₁/M^?1 sec^?1 = 11.66 ± 0.11 – 26.83 ± .31/θ, θ = 2.303RT in kcal/mole. The measured value of E₁, together with the fact that E_?1 = 1 ± 1 kcal/mole, provides ΔH(c-C₄H_7.) = 51.14 ± 1.0 kcal/mole, and the corresponding bond dissociation energy, D(c-C₄H₇? H) = 96.8 ± 1.0 kcal/mole. A bond dissociation energy of 1.8 kcal/mole higher than that for a normal secondary C? H bond corresponds to one half of the extra strain energy in cyclobutene compared to cyclobutane and is in excellent agreement with the recent value of Whittle, determined in a completely different system. Estimates of ΔH and entropy of cyclobutyl iodide are in very good agreement with the equilibrium constant K₁₂ deduced from the kinetic data. Also in good agreement with estimates of Arrhenius parameters is the rate of HI elimination from cyclobutyl iodide.     

Theoretical study of the H 5 + system

Ab initio calculations have been carried out for the ground state of H ₅ ⁺ in order to predict its equilibrium geometry, binding energy, enthalpy of formation, and the features of the H₂ · H ₃ ⁺ interaction at large and intermediate intermolecular distances. The extended basis set of Gaussian functions was carefully optimized to describe the various kinds of intermolecular interactions. Electron correlation was accounted for by means of CI calculations. Different from previous studies we find a D _2d equilibrium geometry with D _e = 7.4 kcal/mol and H ₃₀₀ ⁰ –8.7 kcal/mol. The potential surface turns out to be extremely shallow in the vicinity of the D _2d structure which results in a great mobility of the central nucleus at room temperature.     

Mechanism of hydroformylation,part II Study of the formation of hydrocobalttetracarbonyl by the reaction of Co2(CO)8 and H2

The kinetics and the position of the equilibrium of the reaction Co₂(CO)₈+H₂2 HCo(CO)₄ were studied in the range of 80–160 °C and 50–100 atm. by means of in situ IR spectroscopy.The reaction is reversible first order with respect to CO₂(CO)₈ and HCo(CO)₄ and the energies of activation of the forward and the reverse reaction are found to be 17,3 cal/mole, and 11.0 kcal/mole resp.The reaction is slightly endothermic with H=6.6 kcal/mole and S=14.6 e.u. The heat of formation of HCo(CO)₄ and the bond strength between hydrogen and cobalt in HCo(CO)₄ were found to be—146.1 kcal/mole and 54.7 kcal/mole resp.With 8 FiguresPart of the Ph.D. Dissertation 1974.Part I see Ref.¹³     

Synthesis and properties of 2,2′-dipyridyl and 4,4′-dipyridyl complexes with thulium salts

Summary New complexes of 2,2-dipyridyl and 4,4-dipyridyl with thulium salts TmX ₃ (whereX=Cl^–, Br^–, NO ₃ ^– , NCS^–, and ClO ₄ ^– ) have been prepared and their solubilities in water at 21 °C were determined. The IR spectra of these compounds are discussed. The conditions of thermal decomposition of the complexes were also studied.

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Synthese und Eigenschaften von 2,2-Dipyridyl- und 4,4-Dipyridylkomplexen mit Thuliumsalzen

Zusammenfassung Es wurden neue 2,2-Dipyridyl- und 4,4-Dipyridyl-Komplexen mit Thuliumsalzen TmX ₃ (X=Cl^–, Br^– No ₃ ^– , NCS^–, ClO ₄ ^– ) dargestellt und ihre Wasserlöslihkeit bei 21 °C bestimmt. Die IR-Spektren werden diskutiert. Das thermische Verhalten der erhaltenen Komplexe wurde untersucht.

     

Physicochemical properties of α, ω-type bolaform surfactant in aqueous solution. Eicosane-1,20-bis(triethylammonium bromide)

The physicochemical properties of the, - type (bolaform) surfactant, eicosane-1, 20-bis(triethylammonium bromide) (C₂₀Et₆), in aqueous solution have been investigated by means of surface tension, electrical conductivity, dye solubilization, and time-resolved fluorescence quenching (determination of average micelle aggregation number). Using electrical conductivity, the critical micelle concentration of C₂₀Et₆ was found to be 6.0×10^–3 mol dm^–3 and the ionization degree of C²⁰Et₆ micelle was found to be 0.42. From surface tension measurments, the molecular area of C₂₀Et₆ at the air-water interface was about twice that of normal type surfactants such as dodecyltrimethylammonium bromide (DTAB). The solubilizing power of micellar solution of C₂₀Et₆ toward Orange OT was 1.0×10^–2 mole of dye per mole of surfactant, i. e., slightly smaller than that of DTAB. The micelle aggregation number,N, was found to be 17±2 by time-resolved fluorescence quenching. C₂₀Et₆ showed a very small temperature dependence ofN, much less than for normal surfactants.     

Acid–Base Behavior in Supercritical Water: β-Naphthoic Acid–Ammonia Equilibrium

Equilibrium constants for the reaction of -naphthoic acid and ammonia, K _BHA, were measured with UV-vis spectroscopy in water from 25°C to 400°C. At high density K _BHA decreases with temperature, the normal behavior for an exothermic reaction of a stronger acid and base to a weaker acid and base. At low density, the reaction becomes endothermic as the solvation of the ionic products becomes weaker. These data were combined with literature results for the dissociation of water and ammonia to determine equilibrium constants for the dissociation of -naphthoic acid and the reaction of -naphthoic acid and OH^- Whereas the density (and dielectric constant) of water have only a modest effect on the isocoulombic reaction of -naphthoic acid and OH^-, they have a large effect on all of the other reactions which are ionogenic.     

Determination of the equilibrium melting point of the β-form of polypropylene

The melting behavior of the -form of isotactic polypropylene (-iPP) was investigated as a function of crystallization time and temperature. Calcium suberate, a selective -nucleating agent was used to produce samples that consist entirely of -form i-PP. The experimental melting points were recorded at different crystallization times and were extrapolated to the start of the crystallization process in order to eliminate the effect of lamellar thickening. Using the non-linear Hoffman—Weeks approach to correlate these extrapolated experimental melting temperatures with the corresponding crystallization temperatures, an equilibrium melting point of 209°C was obtained for -iPP. The equilibrium melting point estimated through the non-linear Hoffman—Weeks analysis is about 30°C higher than that (T _m ⁰=177°C) obtained on the basis of the linear extrapolation. These results are consistent with earlier claims that a linear extrapolation of T _m–T _c data leads to an underestimation of the equilibrium melting point. The results obtained for -iPP exemplify the importance of accounting for both the isothermal lamellar thickening effects and the non-linearity in the T _m–T _c correlation, when the determination of an equilibrium melting point is carried out using a procedure based on the predictions of the Lauritzen—Hoffman secondary nucleation theory.This revised version was published online in November 2005 with corrections to the Cover Date.     

Charge-transfer complexes betweenp-toluidine and iodine in solution: A kinetic study

The kinetics of charge-transfer interaction betweenp-toluidine and iodine in methylene chloride was investigated in depth. Thethermal process of formation of theinner complex was found to proceed to an equilibrium. Thephotochemical process follows a different reaction coordinate, going through the formation of an exciplex between the excitedouter complex and the amine ground state. In both cases the same ionic complex (Am ₂I⁺I ₃ ^– , whereAm stands forp-toluidine) was detected as the final product.

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Kinetische Untersuchung der Charge-Transfer-Komplexe zwischenp-Toluidin und Jod

Zusammenfassung Die Kinetik der Charge-Transfer-Wechselwirkung zwischenp-Toluidin und Jod in Methylenchlorid wurde ausführlich untersucht. Derthermische Prozeß, der zur Bildung desinner-Komplexes führt, geht bis zu einem Gleichgewicht. Derphotochemische Prozeß folgt einer unterschiedlichen Reaktionskoordinate und verläuft über die Bildung eines Exziplexes zwischen dem angeregtenouter-Komplex und dem Amin im Grundzustand. In beiden Fällen wurde derselbe ionische Komplex (Am ₂I⁺I ₃ ^– , wobeiAm fürp-Toluidin steht) als Endprodukt festgestellt.

     

Theoretical Study of the Products of Acetylene Addition to HgCl2

The ab initio MP2 method is used with the LANL2DZ basis to calculate the mercury chloride ,-complex with two acetylene molecules (1) and various isomeric forms of mercury di()-vinyl chloride -complexes (2): cis-cis (2A), cis-trans (2B), and trans-trans (2C). The ,-complex is the most stable form of all those considered; the difference between 1 and 2A is 24.9 kcal/mole. A relation between the total energies (kcal/mole) for isomeric forms 2 is established to be 2A (0) < 2B (0.98) < 2C (1.58). Complex 1 is shown to be transformed into 2A via the intermediate formation of 3, which is a hybrid form of the complex (,-complex of mercury chloride with two acetylene molecules). The structures of the transition states for the transformations of 1 into 3 (structure 4) and of 3 into 2A (structure 5) and the corresponding transition activation energies are determined. The interaction of 2A, 2B, and 2C with the Cl^- anion as a model nucleophile is considered. It is shown that the resulting anions (6A, 6B, 6C) have a planar structure with the relative stability increasing in the series 6A<6B<6C.     

Solvation and dissociation of the carbanionic barium salt of the double 1,1′diphenylethylene in tetrahydrofuran

Mono- and dicarbanionic derivatives of 4,4bis(1-phenylethylene)1,1-biphenyl) (BPB): are prepared by addition of cumyl-barium or polystyryl-barium to BPB in tetrahydrofuran (THF). Spectroscopic and conductimetric measurements on monoadduct solutions were carried out in a temperature range from –105 to 25°C. At low temperature these solutions show a large spectral shift, due to the equilibrium between tight and solvent separated ion pairs. The thermodynamic parameters of this two step ion pair solvation were determined and the corresponding dissociation constant was found to be K _d =1×10^–6 mol-dm^–3 at 20°C. Once the first addition completed, the remaining double bond of the monoadduct seems to be less reactive than those of the original BPB. The diadduct has been prepared in the presence of an excess of cumyl-barium, and characterized spectroscopically.     

Thermodynamic properties of the dissociation of several α-oxooximes

The changes in free energy, enthalpy and entropy for the dissociation of several -oxooximes (phenylglyoxal aldoxime, glyoxylanilide oxime,N-ethyl-glyoxylanilide oxime and 1-phenyl-1,2-propanedione-2-oxime) have been determined in water-ethanol medium (50% v/v) at 0.5M ionic strength (NaNO₃) and 25 °C. The changes in dissociation free energy were calculated from the pK _a values determined by glass-electrode potentiometry, and refined by using the programs MINIGLASS and SUPERQUAD. The dissociation enthalpies were determined by direct thermometric titration, and refined by using the programs MINITERM and MULTITERM.