Isotopic study of the mechanism of ozone formation

The mechanism of ozone formation has been studied using ¹⁶O and ¹⁸O₂. High-resolution microwave spectroscopy was used to measure the amounts of the isotopomeric ozone species formed. The study is hampered by the very rapid exchange process between the reactants, that tends to scramble the isotopes and hence give a 2:1 statistical ratio between the two possible isotopomers. We have found a strategy to come around this difficulty and conclude that the mechanism is a simple end-on-addition.     

An investigation of tautomeric equilibria by means of mass spectrometry

Changes in the mass spectra with inlet temperature were used in this work to demonstrate the dependence of keto-enol tautomerism of acetylacetone, 3-methyl acetylacetone and 3-allyl acetylacetone on temperature. The largest dependence of temperature were shown by the ion [M ? 42]^+. arising from a McLafferty type rearrangement and by the ion [M ? Me]⁺ resulting from simple α-cleavage. The ion [M ? 42]^+. peak increases with the temperature of the inlet system while the ion [M ? Me]⁺ peak decreases. By assuming that the ion [M ? 42]^+. represents the keto form and that the ion [M ? Me]⁺ represents the cis-enol form (stabilized by the hydrogen bond) one sees that the direction of the intensity variation of these peaks with temperature is in accord with the expected change of keto-enol tautomerism with temperature. A quantitative correlation on the basis of the above assumptions is also approached. Recording of the mass spectra of these three β-diketones at different energies of the incident electrons enables us to estimate whether or not the particular ions present in the mass spectra result from energetically favourable processes. The variation of the intensities of the peaks with the temperature of the inlet at different electron energies is also discussed.     

An electrochemical study of redox indicators : Part I. Substituted chrysoidines

The electrochemical oxidation of various substituted chrysoidines was studied by cyclic voltammetry, to determine which have stable oxidation products. Only 4-hydroxy-chrysoidine has a stable product; the apparent oxidation potential is 0.779 V vs. NHE. 4-Methoxy- and 4-ethoxy-chrysoidine rapidly lose methanol or ethanol, respectively, so that the 4-hydroxychrysoidine wave appears on subsequent scans. All the other chrysoidines studied are irreversible. The results indicate that a hydroxy group in the 4-position is necessary for stability; the 4-alkoxychrysoidines can achieve the stable quinoidal structure by cleavage of the alkoxy group after nucleophilic attack.     

Construction of orbital angular momentum eigenfunctions for many-particle systems by harmonic projection

Formulas are derived which allow the direct construction of total orbital angular momentum eigenfunctions for many-particle systems without the use of Clebsch–Gordan coefficients. One of the equations is closely analogous to Dirac' identity for the total spin operator. This equation describes the action of L² on a function of the particle coordinates in terms of a class operator of the symmetric group and a "contraction operator." A general projection operator for constructing symmetric eigenfunctions of L² is presented.     

Field desorption mass spectrometry of 1-methylpyridinium salts

Quaternary pyridinium salts were investigated by field desorption, field ionization and electron impact mass spectrometry. Thermal decomposition of the salts under field desorption conditions was found to give very abundant volatile products, identified as the dihydro analogues and the ‘methides’ of the cations. The formation of the volatile compounds, especially those with molecular weights corresponding to those of the (cation ?1), (cation +1) and (cation +13) was studied in detail by deuterium and ¹³C labelling experiments.     

Selective Halogen-Lithium Exchange Reaction of Bromine-Substituted 25,26,27,28-Tetrapropoxycalix[4]arene

Methods are described for the selective bromine-lithium exchange reaction of bromine-substituted calix[4]arenes with either n-BuLi or t-BuLi in THF. Quenching of the lithiated calix[4]arenes with MeOH, D(2)O, CH(3)SSCH(3), B(OCH(3))(3), DMF, or CO(2) as electrophiles resulted in 5-monosubstituted, 5,17-disubstituted, or 5,11,17,23-tetrasubstituted calix[4]arenes with H, D, SCH(3), B(OH)(2), CHO, or COOH functionalities.     

Resistivity of positive-J spin glasses: Study ofLaGd under hydrostatic pressure

Results of a new calculation of the resistivity in the noise model of spin glasses, based on the –J S interaction forpositive J, are compared with measurements of the resistivity in an fcc La-8at% Gd alloy under hydrostatic pressures up to 12 kbar, the first positive-J resistivity investigations under pressure. A positive value ofJ that decreases with increasing pressure, in accord with other experiments, leads to quantitative agreement between theory and experiment if one uses a large electronic density of states at the Fermi energy, in accord with specific heat measurements and electronic band structure calculations in fcc La. Impurity potential scattering is found to contribute significantly to the resistivity. Its size and pressure variation is determined.This work is supported in part by the Deutsche Forschungs-gemeinschaft.     

Field ionization mass spectrometry as a facile method for the study of the thermal formation of radicals

Electron impact spectra of thermolysis products of organic salts heated in the ion source of a mass spectrometer may give rise to organic ions corresponding to the cation of the salt. Field ionization mass spectrometry has been used as a facile method for detemining whether such an ion is due to ionization of the corresponding radical present in the gas phase, or to an electron impact induced fragmentation of a reaction product of higher mass. By comparison of the electron impact and field ionization spectra of a series of N-methyl pyridinium, tropylium and 1,2-dithiolylium salts it has been found possible to identify the radicals formed thermolytically, when present.