Effect of Solvents on Persistent Free Radical Content in the Absence of Reactions
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The impact of a solvent environment on persistent free radical concentrations at ambient conditions was studied by electron spin resonance spectrometry. The analyte selected was Canadian oil-sand-derived bitumen due to its high persistent free radical content. The ability of 54 different solvents to produce a homogeneous 5 wt % solution of bitumen was evaluated. The influence of solvents on the free radical content in bitumen was determined exclusively for solvents that were capable of quantitatively dissolving the bitumen. These were compounds in the classes of alkynes, mono- and bicyclic benzene-derivatives, and heteroatom-containing compounds containing nitrogen, oxygen, sulfur, and chlorine. It was found that a shift in the g-factor of bitumen occurred when the solvent was changed. The shift was attributed to the radical–solvent interaction that is affected by the polarity of the solvent and reflected in the solvent dipole moment property. The change in the free radical concentration was independent of changes in g-factor and was not correlated with any of the following solvent properties: molecular weight, dipole moment, dielectric constant, refractive index, density, and viscosity. There was a relationship between the free radical concentration in bitumen and the ionization potential of sulfur-containing and diaromatic hydrocarbon solvents. It was concluded that the bulk liquid properties that affected the electronic environment of the free radical species, resulting in a shift in g-factor, were not related to the bulk liquid properties that affected the dissociation equilibrium and resulted in a change in the free radical concentration.Keywords:
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A simple and effective method denoted "pH-adjusting" is used to graft a large amount of heteroatoms such as Al and Ti to mesoporous silica material SBA-15. The products prepared by this method show highly ordered mesostructures with large surface areas and uniform mesopore size distribution. The results of ICP, EDX, 27Al NMR, calcium ion-exchange capacity, and UV−vis spectra show that almost all the heteroatoms added into the initial reaction mixture can be introduced into the products, and moreover, the heteroatoms introduced by this route locate at mainly tetrahedrally coordinated sites.
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CONTENTS I. Introduction 311 II. Five-membered heterocycles with one heteroatom 312 III. Five-membered heterocycles with two heteroatoms 314 IV. Five-membered heterocycles with three heteroatoms 319 V. Six-membered heterocycles with one heteroatom 320 VI. Six-membered heterocycles with two heteroatoms 320 VII. Condensed heterocyclic systems with several heteroatoms 322
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This chapter contains sections titled: Introduction Five-membered systems with one heteroatom Five-membered systems with two heteroatoms Five-membered ring systems with more than two heteroatoms Six-membered heterocycles containing one heteroatom Six-membered heterocycles containing at least two heteroatoms Seven-membered heterocycles containing at least two heteroatoms: 1,4 and 1,5-benzodiazepines Polycyclic heterocycles Conclusion References
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This chapter contains sections titled: Three-Membered Heterocycles with One Heteroatom Four-Membered Heterocycles with One Heteroatom Five-Membered Heterocycles with One Heteroatom Five-Membered Heterocycles with Two Heteroatoms Five-Membered Heterocycles with Three Heteroatoms Five-Membered Heterocycles with Four Heteroatoms Six-Membered Heterocycles with One Heteroatom Six-Membered Heterocycles with Two Heteroatoms Six-Membered Heterocycles with Three Heteroatoms Larger Heterocyclic and Polycyclic Ring Systems References
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