RESUMO
In this study, we report the first chemical characterization of a plasma-deposited model fluoropolymer on low-k dielectric nanostructure and its decomposition in UV/O2 conditions. Carbonyl incorporation and progressive removal of fluorocarbon fragments from the polymer were observed with increasing UV (≥230 nm) irradiation under atmospheric conditions. A significant material loss was achieved after 300 s of UV treatment and a subsequent wet clean completely removed the initially insoluble fluoropolymer from the patterned nanostructures. A synergistic mechanism of UV light absorption by carbonyl chromophore and oxygen incorporation is proposed to account for the observed photodegradation of the fluoropolymer.
RESUMO
Structural and mechanistic studies of the lithium diisopropylamide (LDA)-mediated anionic Fries rearrangements of aryl carbamates are described. Substituents at the meta position of the arene (H, OMe, F) and the dialkylamino moiety of the carbamate (Me(2)N, Et(2)N, and i-Pr(2)N) markedly influence the relative rates of ortholithiation and subsequent Fries rearrangement. Structural studies using (6)Li and (15)N NMR spectroscopies on samples derived from [(6)Li,(15)N]LDA reveal an LDA dimer, LDA dimer-arene complexes, an aryllithium monomer, LDA-aryllithium mixed dimers, an LDA-lithium phenolate mixed dimer, and homoaggregated lithium phenolates. The highly insoluble phenolate was characterized as a dimer by X-ray crystallography. Rate studies show monomer- and dimer-based ortholithiations as well as monomer- and mixed dimer-based Fries rearrangements. Density functional theory computational studies probe experimentally elusive structural and mechanistic details.
Assuntos
Ânions/química , Carbamatos/química , Hidrocarbonetos Aromáticos/química , Lítio/química , Compostos Organometálicos/química , Propilaminas/química , Cristalografia por Raios X , Dimerização , Cinética , Espectroscopia de Ressonância Magnética , Modelos QuímicosRESUMO
Lithium diisopropylamide-mediated dehydrobrominations of exo-2-bromonorbornane, 1-bromocyclooctene, and cis-4-bromo-tert-butylcyclohexane were studied in THF solutions and THF solutions with added hexamethylphosphoramide (HMPA). Rate studies reveal a diverse array of mechanisms based on mono-, di-, and trisolvated monomers as well as triple ions. The results are contrasted with analogous eliminations in THF in the absence of HMPA.