The reduction of osmium tetroxide by a series of alcohols was studied spectrophotometrically. The reaction was observed to occur in two steps, unlike previously reported studies on this reaction. The identities of both reactants and products were established via a range of techniques. Equilibrium and kinetic data were gathered and reaction models were evaluated using equilibrium and kinetic modelling software. The following complexation reaction model emerged that simulates both the equilibrium and kinetic data. Os(VIII) + RCH2OHOs(VI) + RCHO2 Os(VIII) + Os(VI)k+2k1Complexk-2 Conditional rate constants and equilibrium constants were generated. Rate constants for the alcohol reactions were correlated with the Taft σ* constant. The ρ* value obtained (-1.4) is consistent with a hydride transfer mechanism coupled with synchronous removal of the hydroxyl proton. The identity of the osmium(VIII)-osmium(VI) complex has been suggested. Thermodynamic parameters were also reported. The rate constants for benzyl alcohol and 2-chloroethanol deviated from those predicted by the Taft plot. An explanation of enhanced resonance effects is offered for benzyl alcohol and an alternative reaction mechanism, involving proton abstraction, is offered for 2-chloroethanol. The reaction of the oxidation products of alcohols, namely ketones, with osmium tetroxide produced rate constants that were, perhaps surprisingly, far larger than those of the alcohols. A reaction mechanism for the oxidation of the ketones is suggested, which involves the enolate ion as the reactive starting reagent.

No description available.

The phase behaviour of methane at temperatures below 20°K is still not understood. There is recent evidence for a second phase transition at 8°K, in addition to the well known transition at 20.4°K. This second transition requires a long time to reach equilibrium. In our experiment, the nuclear magnetic resonance signal of the methane protons was monitored for a period of many hours at 1.2°K, in order to; determine whether a slow phase change occurred in the approach to equilibrium. This change would manifest itself in the width of the resonance line, which is sensitive to the local environment of the proton, and thus able to provide information about the crystal structure. No definite time variation of line width was observed. The line width increased by 15% from 4.2°K to 1.2°K. The second moment of the line also rose sharply as the temperature increased, indicating an increasing contribution to the spin-spin interaction from intra-molecular broadening. An approximate model yielded a correlation time for the intra-molecular term of the order of a microsecond. Significant differences between different methane samples indicate that sample preparation is important, and that the above results were for samples in some sort of metastable phase. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In order to study quantitatively the acidity of very weak acids and at the same time the effect of a polar aprotic solvent on the basicity of hydroxide ion a Hammett H_ acidity function based on the ionization of 24 substituted anilines and diphenylamines has been established in the system dimethylsulfoxide-water-tetramethylammonium hydroxide. The basicity of hydroxide ion is increased dramatically as the solvent is changed from water to dimethylsulfoxide. The H_ of a 0.011 molar solution of tetramethylammonium hydroxide ranges from 12 in water to 26 in 99.6 mole % dimethylsul-foxide-water, an increase in basicity of fourteen powers of ten. The increase in basicity is due to the increased activity of the hydroxide ion brought about by the reduction in its solvation in the poor anion-solvating solvent, dimethyl sulfoxide and indicates the extensive solvation enjoyed by the hydroxide ion in water. The pKHA values of the indicator acids vary from 13.84 for 2,4-dinitrodiphenylamine to 25.63 for 3-chloroaniline. From a plot of log KHA versus Hammett substituent constants ( ϭ) for six monosubstituted diphenylamines a rho (ρ) value of 4.07 is found. The magnitude of substituent effects on the acidity of aniline appears to be quite similar. The acidities of all the substituted diphenylamines do not follow the above mentioned correlation with Hammett ϭconstants; the pKHA values of 4-amino-, 4-methoxy-, 4-methylsulfonyl-, and 4-nitrodiphenylamine are all less than expected from the Hammett ϭ constants for the substituents in these compounds. The 4-nitro substituent exerts a particularly large acid-strengthening effect on the acidities of aniline and diphenyl amine; the decreases in pKHA being approximately 8.4 and 6.8 pK units, respectively. The pKHA values of 17 compounds other than those indicators used to establish the H_ function have been determined with the aid of the H_ function. Most of these compounds are alkyl-substituted 4-nitroanilines. Alkyl groups ortho to the amino group of 4-nitroaniline cause a decrease in the pKHA (an increase in acidity). Similarly, N-methyl-, N-ethyl-, and N-isopropyl-4-mitro- aniline are all stronger acids than 4-nitroaniline itself. An explanation for the effects of alkyl substituents on the acidity of 4-nitroaniline in terms of the solvation of both the ionized and unionized amines is advanced. A Hammett Hₒ acidity function based on the protonation of 17 diphenylamines in 20 volume % ethanol-aqueous sulfuric acid has been established. The Hₒ value for the most acidic solution studied is -6.97 for 11.2 molar sulfuric acid. This acidity function differs from that based on the protonation of azobenzenes in the same solvent system; the latter acidity function diverges to more, negative Hₒ values as the sulfuric acid concentration increases. The pKBH+ values for the protonation of the diphenylamines vary from 1.36 for 4 methoxydiphenylamine to -6.21 for 4,4'-dinitrodiphenylamine. A plot, of log KBH+ versus Hammett ϭ constants for five mono-substituted diphenylamines yields a rho (ρ) value of.3.36. The pKBH+ values for 4-methoxy-, 4-methyl-, 4-methylsulfonyl-, and 4-nitro-diphenylamine are all less (morenegative) than expected from the Hammett substituent constants. Substituent effects on the basicities of aniline and diphenylamine are the same. This is evident from the fact, that a plot of the pKBH+ values of 11 diphenylamines versus the pKBH+ values of the corresponding anilines yields a good straight line with slope 1.01. The basicities of several nitro-substituted diphenylamines appear to vary regularly and do not reflect the presence of a strong interaction between the nitro group and sulfuric acid. A plot of the acidity versus the basicity (pKHA versus pKBH+) for nine diphenylamines yields, a straight line with slope 1.30. In a similar plot for 33 substituted anilines and diphenylamines two types of behaviour are observed. Those anilines and diphenylamines without an ortho or para hitro group fall about the line with slope 1.30 while those amines with at least one nitro group in the ortho or para position fall on a different, curved line with a slope of less than unity. / Science, Faculty of / Chemistry, Department of / Graduate

In this thesis, we develop a perturbative formulation of non-equilibrium thermal quantum field theory, capable of describing the evolution of both temporal and spatial inhomogeneities in relativistic, quantum-statistical ensembles. We begin with a review of the necessary prerequisites from classical thermodynamics, classical and quantum statistical mechanics, quantum field theory and equilibrium thermal field theory. Setting general boundary conditions on the ensemble expectation values of products of interaction-picture creation and annihilation operators, we derive free propagators in which space-time translational invariance is explicitly broken. By means of the Schwinger-Kelydsh, closed-time path formalism, we are then able to introduce a path-integral description that accounts consistently for these temporal and spatial inhomogeneities. Subsequently, we develop a time-dependent perturbation theory that is free of the pathologies previously thought to spoil such approaches to non-equilibrium dynamics. Following an unambiguous definition of the number density of particles, we derive from first principles perturbative, field-theoretic evolution equations for statistical distribution functions. These evolution equations do not rely on the gradient expansion of so-called Wigner functions, as is necessary in the alternative Kadanoff-Baym approach, and are consistent with the well-known Boltzmann equations in the classical limit. Finally, with reference to a simple toy model, we highlight the appearance of processes otherwise kinematically disallowed in existing approaches to thermal field theory. These evanescent contributions are a consequence of the microscopic violation of energy conservation and are shown to be significant to the early-time evolution of non-equilibrium systems. We observe that the spectral evolution oscillates with time-dependent frequencies, which is interpreted as a signal of non-Markovian, memory effects.

A general algorithm for the computation of chemical equilibria in complex systems containing non-ideal solutions has been developed. The method is a G-minimization based on repeated linear and nonlinear programming steps. A computer program (THERIAK) based on this algorithm has been written and was used to solve a great variety of problems, ranging from a simple blast furnace calculation to liquid-liquid unmixing in a four component silicate melt. The computing times are in the magnitude of 1/2 to 2 seconds for each calculation. The method can also be used to test the consequences of thermodynamic models and data in systems of interest to many fields, including chemistry, geochemistry and metallurgy. Integrated powder diffraction intensities can be used to measure Mn-Mg and Fe-Mg site occupancies in olivines because of the difference in scattering factors between Mg and Mn or Fe. Theoretically calculated intensity ratios are subject to uncertainties from positional parameters (less than 3.5 % for peaks with a relative intensity greater than 25 %) and unknown charge distribution (up to 30 %). Several peak ratios are less subject to this last uncertainty and may be used to measure the site occupancies in olivines. 27 synthetic Fe-Mn-Mg olivines (800 °C, vacuum, with graphite) were investigated with Mossbauer spectroscopy and XRD intensity evaluation, producing occupancies accurate to approximately 0.03 per site. A thermodynamic speciation model represents the data very well. Preliminary Fe-Mn-Mg exchange experiments involving olivine and garnet place some limits on element distributions between these two minerals. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 1977 / Includes bibliographical references. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Chemistry

Solid-liquid phase equilibria studies were used to investigate possible compound formation in solutions of (i) N,N-dimethylformamide (DMF) and (ii) N,N-dimethylacetamide (DMA) with a series of halogenated hydrocarbons that were selected to give a wide range of acceptor properties. Solid 1:1 intermolecular compounds were identified from solutions of (i) DMF and (ii) DMA with CCl_4, CBrCl_3, and C_6H_5CCl_3. The intermolecular compounds (DMF)_2•CCl_4 and (DMF)_2•CBrCl_3 were also found. The results suggest charge transfer from DMF or DMA to the chlorine atoms of the acceptor molecule as the process for compound formation. Thermal methods were used to determine with high precision the solid-liquid phase equilibria diagram for the sodium-cesium system. Results differ greatly from those of earlier workers, especially near the eutectic composition where differences in melting points as large as 35°K occur. Although not conclusive, results support the proposal that the peritectic halt results from the formation of an Na_2Cs intermetallic compound by a very sluggish reaction. Thermal methods were also used to determine the mesophase transition temperatures for cholesteryl formate.

Thermodynamic equilibrium constants were obtained potentiometrically using a Beckman pH meter for metal-serine and metal-thioglycolloc acid complexes to study the thermodynamic properties of the complexes and the effect of dπ - dπ bonding on the equilibrium constants. The following calculations were made: 1. The stepwise dissociation of protons from serine at 10, 20, 30, and 40°C and the stepwise dissociation of protons from thioglycollic acid at 20, 30, and 40°C. 2. The thermodynamic formation constants for Zn(II), Cd(II), Hg(II), and Ag(I) with serine at 10, 20, 30, and 40°C and at two ionic strengths. 3. The thermodynamic formation constants for Zn(II), Cd(II), Hg(II), and In(III) with thioglycollic acid at 20 and 30°C and at two ionic strengths. 4. The entropy, enthalpy, and free energy change for each of the metal-serine complexes. The order of increaseing stability of log K_1 for the metal-serine systems was as follows: Hg(II) > > Zn(II) > Cd(II) > Ag(I), and for log K_2 the order: Hg(II) > > Zn(II) > Cd(II) ≈ Ag(I). The stability of the Hg(II)-serine was high becasue of the high electronegativity of Hg(II) and an abundance of 4f and 5d electrons that can be polarized by the ligand donor atoms. Values for log K_1 of Zn(II), Cd(II), and Ag(I) with serine decreased in the order of decreasing electronegativity of the metal ions. All log K_2 values were smaller than log K_1 values and followed the same order of stability as log K_1 with the exception of the Ag(I)-serine complex. Linear bonding is more stable for Ag(I) than any other spatial configuration. The second formation constant is this higher than the first because the second ligand completes this stable linear complex. In(III) precipitated as a hydroxide, making it impossible to measure a formation constant for In(II) with serine. The order of increasing stability of log K_1 for the metal-thiogly-colloc acid system was as follows: Hg(II) In(III) Cd(II) Zn(II) and for log K_2 the order: Hg(II) Zn(II) In(III) Cd(II). Log K_1 values for Hg(II) In(III), and Cd(II) were above 10 indicating that these metal ions form an extremely stable bond with sulfur. This enhanced stability is due to the formation of a second bond or a d - d bond between the metal ion and the sulfur atom. The d bonding with Zn(II) is not as great as with the other metal ions. The order is somewhat reversed for log K_2 and follows the order of decreasing electronegativities of the metal ion. This would indicate that the d bonding is not as pronounced in the second formation constant. Hg(II) again has a high log K_2 value because of the electronegativity of Hg(II) and the 4f and 5d polarizable electrons. The Ag(I)-thioglyeollic acid complex could not be calculated because Ag(I) precipitated with thioglycollic acid.