Do persistent organic pollutants reach a thermodynamic equilibrium in the global environment?

Equilibrium partitioning between different environmental media is one of the main driving forces that govern the environmental fate of organic chemicals. In the global environment, equilibrium partitioning is in competition with long-range transport, advective phase transfer processes such as wet deposition, and degradation. Here we investigate under what conditions equilibrium partitioning is strong enough to control the global distribution of organic chemicals.

Chiral modification of platinum by co-adsorbed cinchonidine and trifluoroacetic acid: origin of enhanced stereocontrol in the hydrogenation of trifluoroacetophenone.

Cinchonidine (CD) adsorbed onto a platinum metal catalyst leads to rate acceleration and induces strong stereocontrol in the asymmetric hydrogenation of trifluoroacetophenone. Addition of catalytic amounts of trifluoroacetic acid (TFA) significantly enhances the enantiomeric excess from 50 to 92%. The origin of the enantioselectivity bestowed by co-adsorbed CD and TFA is investigated by using in situ attenuated total reflection infrared spectroscopy and modulation excitation spectroscopy.

Synthesis and evaluation of new guanidine-thiourea organocatalyst for the nitro-Michael reaction: Theoretical studies on mechanism and enantioselectivity.

A new guanidine-thiourea organocatalyst has been developed and applied as bifunctional organocatalyst in the Michael addition reaction of diethyl malonate to trans-β-nitrostyrene. Extensive DFT calculations, including solvent effects and dispersion corrections, as well as ab initio calculations provide a plausible description of the reaction mechanism.

Assessment of Popular DFT and Semiempirical Molecular Orbital Techniques for Calculating Relative Transition State Energies and Kinetic Product Distributions in Enantioselective Organocatalytic Reactions.

The performance of computationally accessible levels of calculation for the transition states of organocatalytic reaction has been assessed. Reference post-Hartree-Fock single point energy calculations were used as standards for the gas-phase Born-Oppenheimer relative energies of pairs of alternative transition states that lead to the two product enantiomers. We show that semiempirical methods cannot even be relied on to yield qualitatively correct results.

Chiral BINOL-derived phosphoric acids: privileged Brønsted acid organocatalysts for C-C bond formation reactions.

BINOL-derived phosphoric acids have emerged during the last five years as powerful chiral Brønsted acid catalysts in many enantioselective processes. The most successful transformations carried out with chiral BINOL phosphates include C-C bond formation reactions. The recent advances have been reviewed in this article with a focus being placed on hydrocyanations, aldol-type, Mannich, Friedel-Crafts, aza-ene-type, Diels-Alder, as well as cascade and multi-component reactions.

Enantioselective nitro-Michael reactions catalyzed by short peptides on water.

Simple unmodified N-proline-based di- and tripeptides in combination with sodium hydroxide additive catalyze the asymmetric Michael reaction of ketones with nitroolefins to furnish the corresponding gamma-nitroketones with up to 99% yield, 99:1 dr and 70% ee at room temperature and on water without any organic cosolvent.