Radical Clock Reactions under Pseudo-First-Order Conditions Using Catalytic Quantities of Diphenyl Diselenide. A 77Se- and 119Sn-NMR Study of the Reaction of Tributylstannane and Diphenyl Diselenide

Adsorption of CO2 by surface modified coal-based activated carbons: kinetic and thermodynamic analysis

The effects of different surface modifiers on the CO2 adsorption capacity of coal-based activated carbons were studied, and the diffusion behavior, adsorption kinetics and thermodynamic parameters of CO2 in activated carbons were analyzed. The results show that compared with ethylene glycol, 1,2-propylenediamine and zinc chloride, potassium hydroxide and sodium hydroxide can greatly improve CO2 adsorption capacity. The adsorption rate is faster, and the adsorption capacity is larger, with the maximum CO2 adsorption capacity being 33.54 mL/g. Fick’s law can well describe the diffusion behavior of CO2 in activated carbon. The addition of a surface modifier can increase the diffusion coefficient. The diffusion of CO2 in activated carbon falls into the category of crystal diffusion. The adsorption kinetics of CO2 before and after surface modification follow the Bangham equation. During the adsorption process, δ H < 0, δ G < 0, δ S < 0. Surface modification can reduce adsorption heat and promote adsorption, and the adsorption process is dominated by physisorption.

Aromatic diselenide crosslinkers to enhance the reprocessability and self-healing of polyurethane thermosets

We explore the utilization of aromatic diselenides as new low temperature exchangeable monomers for their utilization in thermosets.

Chalcogenol ligand toolbox for CdSe nanocrystals and their influence on exciton relaxation pathways

We have employed a simple modular approach to install small chalcogenol ligands on the surface of CdSe nanocrystals. This versatile modification strategy provides access to thiol, selenol, and tellurol ligand sets via the in situ reduction of R2E2 (R=tBu, Bn, Ph; E=S, Se, Te) by diphenylphosphine (Ph2PH). The ligand exchange chemistry was analyzed by solution NMR spectroscopy, which reveals that reduction of the R2E2 precursors by Ph2PH directly yields active chalcogenol ligands that subsequently bind to the surface of the CdSe nanocrystals. Thermogravimetric analysis, FT-IR spectroscopy, and energy dispersive X-ray spectroscopy provide further evidence for chalcogenol addition to the CdSe surface with a concomitant reduction in overall organic content from the displacement of native ligands. Time-resolved and low temperature photoluminescence measurements showed that all of the phenylchalcogenol ligands rapidly quench the photoluminescence by hole localization onto the ligand. Selenol and tellurol ligands exhibit a larger driving force for hole transfer than thiol ligands and therefore quench the photoluminescence more efficiently. The hole transfer process could lead to engineering long-lived, partially separated excited states.

The kinetics of carbonyl radical ring closures

Kinetic data for intramolecular homolytic substitution reactions of a series of acyl and oxyacyl radicals are reported.

Catalysis of stannane-mediated radical chain reactions by benzeneselenol

The discovery and development of the catalysis of stannane-mediated radical chain reactions by benzeneselenol, generated in situ by reduction of diphenyl diselenide with tributyltin hydride, are described. The catalytic sequence is discussed in terms of polarity reversal catalysis of radical chain reactions, and applications to synthesis are presented. These include the prevention of numerous radical rearrangement reactions, the ability to intervene in certain multistep radical rearrangements, especially aryl and vinyl radical cyclizations, at intermediate stages with advantages to the product profile, and the effective trapping of allyl-, benzyl-, and cyclohexadienyl-type radicals, permitting inter alia the isolation of aryl cyclohexadienes and their application in synthesis.

5-Endo-Dig Radical Cyclizations: “The Poor Cousins” of the Radical Cyclizations Family

Kinetics and thermodynamics of 5-endo-dig radical cyclizations were studied using a combination of DFT computations and Marcus theory. When the reactant is stabilized by conjugation of the radical center with the bridge pi-system, the cyclization starts with reorientation of the radical orbital needed to reach the in-plane acetylene pi-orbital in the bond-forming step. This reorientation leads to loss of the above conjugative stabilization, increases the activation energy, and renders such cyclizations less exothermic. As a result, even when the radical needed for the 5-endo cyclization is formed efficiently, it undergoes either H-abstraction or equilibration with an isomeric radical. Only when the bridging moiety is saturated or when intramolecular constraints prevent the overlap of the bridge pi-orbital and the radical center, 5-endo cyclizations may be able to proceed with moderate efficiency under conditions when H-abstraction is slow. The main remaining caveat in designing such geometrically constrained 5-endo-dig cyclizations is their sensitivity to strain effects, especially when polycyclic systems are formed. The strain effects can be counterbalanced by increasing the stabilization of the product (e.g., by introducing heteroatoms into the bridging moiety). Electronic effects of such substitutions can be manifested in various ways, ranging from aromatic stabilization to a hyperconjugative beta-Si effect. The 4-exo-dig cyclization is kinetically competitive with the 5-endo-dig process but less favorable thermodynamically. As a result, by proper design of reaction conditions, 5-endo-dig radical cyclizations should be experimentally feasible.