RESUMO
We present an experimental study of a cyclooctatetraene-based molecular balance disubstituted with increasingly bulky tert-butyl (tBu), adamantyl (Ad), and diamantyl (Dia) substituents in the 1,4-/1,6-positions for which we determined the valence-bond shift equilibrium in n-hexane (hex), n-octane (oct), and n-dodecane (dod). Computations including implicit and explicit solvation support our temperature-dependent NMR equilibrium measurements indicating that the more sterically crowded 1,6-isomer is always favored, irrespective of solvent, and that the free energy is quite insensitive to substituent size.
RESUMO
Diamondoids, sp3 -hybridized nanometer-sized diamond-like hydrocarbons (nanodiamonds), difunctionalized with hydroxy and primary phosphine oxide groups, enable the assembly of the first sp3 -C-based chemical sensors by vapor deposition. Both pristine nanodiamonds and palladium nanolayered composites can be used to detect toxic NO2 and NH3 gases. This carbon-based gas sensor technology allows reversible NO2 detection down to 50â ppb and NH3 detection at 25-100â ppm concentration with fast response and recovery processes at 100 °C. Reversible gas adsorption and detection is compatible with 50 % humidity conditions. Semiconducting p-type sensing properties are achieved from devices based on primary phosphine-diamantanol, in which high specific area (ca. 140â m2 g-1 ) and channel nanoporosity derive from H-bonding.
RESUMO
We present a new acid-free method for the generation of carbocations based on a redox condensation reaction that enables SN1 reactions with a variety of nucleophiles. We utilize readily synthesized phosphinites that are activated by diisopropyl azodicarboxylate to form betaine structures that collapse upon adding a pronucleophile, thereby yielding reactive carbocation intermediates. We also employ this approach for the alkylation of some bioactive molecules.
RESUMO
We report a general and scalable method for the synthesis of all-meta-trisubstituted benzenes from readily available 3,5-disubstituted catechols. Oxidation and [4 + 2] cycloaddition with acetylene dienophiles generate a bicyclo[2.2.2]octane structure that is doubly decarbonylated initiated by blue-light irradiation, leading to a meta,meta-disubstitution pattern on the re-aromatized system. This enables this substitution pattern even with very bulky alkyl groups (deemed excellent dispersion energy donors) to be incorporated into, for example, chiral phosphoric acid catalysts.