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The experimental work described in this thesis is designed to give information on the thermodynamic properties and chemical reactivity of the surface of an ionic crystal. The principal studies concern halogen exchange between hydrogen chloride gas and the surface of sodium bromide. For this reaction, like any ordinary chemical reaction, both kinetics and equilibrium may be investigated. In the present study, the most Interesting feature has been the measurement of the equilibrium constant and the calculation therefrom of the changes in thermodynamic properties attending the replacement of a bromide ion by a chloride ion in the surface. This appears to be the first reported measurement of an equilibrium constant involving concentrations in a solid surface. The work differs sharply from previous studies of isotopic exchange, which have been exclusively kinetic. The equilibrium is best represented by the equation [formula omitted] where X and (1-X) are the fractions of the surface anion sites occupied by Cl⁻ and Br⁻ respectively, ∆°S refers to the entropy changes of the exchanged ions at X = 0, and Si(X) describes the effect of any anion on the entropy of its neighbours in the surface. The equation indicates the formation of a two-dimensional solid solution of NaCl and NaBr, deviating from ideality through the term Si(X), so that the equilibrium constant K is a function of X. Since K is independent of temperature (20°-95°C.), ∆H = 0 and the equilibrium equation contains entropy terms only. From the value K = 6X10⁻³ at X = 0 it is estimated that [formula omitted] where S°Cl⁻ and S°Br⁻ refer to surface ions. The variation of K with X is used to arrive at a tentative estimate, based on some simplifying assumptions, of [formulas omitted]. Of this, about -2 cal/mole deg. K may be a simple mass effect. These large decreases in entropy are discussed in relation to the probable structure of the surface of sodium bromide; they are consistent with the "Verwey distortion" in which the anions are displaced outwards from the ideal surface, the distortion increasing, ceteris paribus, with the size and polarizability of the anions. The kinetics of the exchange reaction have been studied. It has not proved possible to analyze the rate curves in detail. The most striking feature, in comparison with previous studies, is that all reactions involving bromine (initially in either the gaseous or the solid phase) are faster than those involving chlorine isotopes only. The reason for this may be either the availability of d-orbitals of bromine for bonding in a transition complex, or the polarizability of the bromine atom. The exchange reaction has been used to study diffusion of chloride ions into sodium bromide at room temperature. It is possible to measure diffusion coefficients of about 10⁻²²cm²sec⁻¹, smaller by a factor of about 10⁵ than can be measured by most conventional methods. The results suggest that diffusion takes place principally along dislocations. The dehydration of high surface area sodium bromide has been studied, and is found to take place at a vapour pressure different from the equilibrium value for the system, NaBr.2H₂0; NaBr; H₂O. This is attributed to the formation of a "surface hydrate" overlying the lattice of anhydrous NaBr. This process may be regarded as adsorption with a discontinuous isotherm, and implies that the NaBr surface is energetically homogeneous. It has been found that color centers may readily be produced in the alkali halides by a Tesla Coil discharge. Centers thus produced in sodium chloride have been examined spetroscopically. The technique may be useful in experiments to establish the mechanism of exchange reactions such as that described in this thesis. / Science, Faculty of / Chemistry, Department of / Graduate

La synthèse organique est une science centrale dont les applications se reflètent dans de nombreux domaines tels que la médecine, l’agrochimie, l’énergie ou encore les sciences des matériaux. En outre, l’évolution constante de ces domaines implique une demande croissante de nouveaux procédés courts, efficaces et peu couteux permettant la synthèse de molécules complexes au départ de briques élémentaires simples. De plus, la nécessité pressante de développer des procédés respectueux de l’environnement entraine également l’apparition de nouveaux défis qui reposent non seulement sur l’utilisation de nouveaux réactifs et catalyseurs, mais également sur le développement de nouvelles méthodologies permettant d’assembler des molécules de manière plus durable. Dans ce contexte, les ynamides représentent des candidats particulièrement attractifs pour la mise au point de nouvelles méthodes en synthèse organique. En effet, le développement d’une variété de procédés généraux et efficaces permettant la synthèse de ces alcynes aza-substitués a permis de faciliter la conception d’une série de transformations utiles et innovantes. Plus particulièrement, les ynamides ont au cours des deux dernières décennies fait preuve d’un excellent équilibre entre réactivité et stabilité. La forte polarisation de leur triple liaison, subtilement tempérée par la présence d’un groupement électroattracteur sur l’atome d’azote, permet non seulement la génération aisée d’intermédiaires hautement réactifs, mais également le développement de réactions régio et/ou stéréosélectives. Plus précisément, les ynamides ont été utilisés dans diverses réactions incluant des additions nucléophiles, des additions électrophiles, des cycloadditions ainsi que des cyclisations radicalaires. Toutefois, la chimie des ynamides repose le plus souvent sur leur mode de réactivité cationique, qui consiste en leur activation avec un réactif électrophile, suivie du piégage de l’ion cétèniminium résultant par un nucléophile interne ou externe, et de l’initiation de transformations subséquentes variées.Bien que la chimie des ynamides soit à l’origine du développement d’une série de procédés efficaces dont les applications couvrent la plupart des domaines proéminents de la chimie organique tels que la synthèse hétérocyclique, la synthèse asymétrique ou encore la chimie organométallique, de nombreux aspects de leur réactivité restent encore aujourd’hui sous exploités. Dans ce contexte, le travail décrit dans ce manuscrit portera sur le développement de nouvelles réactions basées sur la chimie cationique des ynamides. Plus précisément, ce manuscrit sera subdivisé en trois chapitres décrivant :i) Une étude bibliographique détaillant la chimie cationique des ynamides, ii) Le développement d’une réaction d’halogénation d’ynamides, iii) Le développement d’une réaction d’hydroalkylation intramoléculaire d’ynamides. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

A procedure was developed for dealing with two problems that have impeded the use of quantal parameters in studies of transmitter release. The first, involving temporal and spatial biasing in the estimates for the number of functional release sites (n̄) and probability of release (p̄), was addressed by reducing temporal variance experimentally and calculating the bias produced by spatial variance in p (var(s)p). The second, involving inaccuracies in the use of nerve-evoked endplate potentials (EPPs), was circumvented by using only miniature EPPs (MEPPs). Intracellular recordings were made from isolated frog cutaneous pectoris, after decapitation and pithing of the animals, and the concentration of K+ ([K+]) was raised to 10 mM to increase the level of transmitter release. The number of quanta released (m̄) by the EPP was replaced by the number of MEPPs in a fixed time interval (bin), and 500 sequential bins used for each quantal estimate. With the use of 50-ms bins, estimates for var(s)p were consistently negative. This was due to too large a bin (and introduction of undetected temporal variance) because the use of smaller bins (5 ms) produced positive estimates of var(s)p. Increases in m, n, and p but not var(s)p were found in response to increases in [K+] or [Ca2+]/[Co2+]. La3+ (20 μM) produced increases in m and n, which peaked after 20 min and declined toward zero. There were also large increases in p and var(s)p, which peaked and declined only to initial control values. The increase in var(s)p was presumed to reflect La3+-induced release of Ca2+ from intracellular organelles. The results suggest that this approach may be used to obtain unbiased estimates of n̄ and p̄ and that the estimates of var(s)p may be useful for studying Ca2+ release from intraterminal organelles.

The microwave-resonant-cavity technique was employes as a probe to determine the presence of molecular ions of helium in a d.c.-discharge, helium-plasma filament placed coaxially in a TM010 mode cavity. The cavity-resonance profile was displayed on an oscilloscope, and the nature of the perturbation of this resonance was used to determine the nature of the ions present in the plasma stream.

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