Rina Dao

Modification of the Onsager Reaction Field and Its Application on Spectral Parameters

Solvent polarity is an important solvent property. The Onsagers theory of reaction field was the most classic model to describe solvent effects and was widely used in relating dielectric constant and other solvent polarity parameters. In this study, a modified semi-empirical reaction field was presented to relate electron transition energies or hyperfine coupling constants with the dielectric constants of solvents. In previous work, this relationship was well established by traditional Onsager reaction field for nonhydrogen-bonding systems but failed for hydrogen-bonding systems. In this modified reaction field model, the radius of the field was replaced by that of the primary solvation shell or the molecular fragment rather than that of the probe. In this way, the molecular volume of the solvent which contains information of the molecular size and overall interactions is involved in the reaction field. The 154 sets of electron transition energies and 44 sets of nitrogen isotropic hyperfine coupling constants were used to verify the modified model, indicating it works far better than the traditional model for hydrogen-bonding systems.

Distinguishing Ionic and Radical Mechanisms of the Hydroxylamines Mediated Electrocatalytic Alcohol Oxidation using the NO-H Bond Dissociation Energy

The mechanism of N-oxyl radical catalyzed oxidation is a long-standing scientific problem. In this work, radical or ionic mechanisms in electrocatalytic oxidation of alcohols are discussed on the NO-H bond dissociation energy (BDE) scale. A thermodynamic model was built to outline the range of BDEs for the catalysts that react via the two mechanisms. The N-oxyl radical catalyzed electrocatalytic benzyl alcohol oxidations with NO-H BDEs smaller than 74 kcal mol-1 reacted by an ionic mechanism, and with BDEs greater than 78 kcal mol-1 reacted by a radical mechanism. Oxidizing aliphatic alcohols via a radical mechanism requires catalysts with BDEs even greater than that of N-hydroxyphthalimide (NHPI), and the ionic mechanism requires catalysts with BDEs smaller than 74 kcal mol-1. With either the ionic or radical mechanism, catalysts with larger BDEs correspond to a smaller activation energy of the key step. Future design of N-oxyls with catalytic activity in alcohol oxidation can be streamlined by our efforts.

N-Hydroxyphthalimide (NHPI) Promoted Aerobic Baeyer-Villiger Oxidation in the Presence of Aldehydes

Metal‐free aerobic Baeyer‐Villiger (BV) oxidation of ketones to lactones or esters in the presence of aldehydes promoted by N‐hydroxyphthalimide (NHPI) has been developed. The reaction proceeded under mild conditions with excellent selectivity and high yields. Compared with the methods that use metal complexes as catalysts, this strategy not only showed good environmental advantages, but also increased aldehyde efficiency up to 84 %. Control experiments indicated that NHPI accelerated the oxidation of aldehydes to peroxy acids but did not improve the BV oxidation while peroxy acids were already generated. Peroxy acids generated from aldehydes in situ were the key intermediates, and the phthalimide‐N‐oxyl radical (PINO) contributed to high aldehyde efficiency by stabilizing the radical species, which are necessary for the chain propagation reactions. This study may offer some useful strategies for new transition metal‐free catalytic aerobic oxidation reactions in which aldehydes act as sacrificial agents.