The reaction of acyl peroxides with 2,2,6,6-tetramethylpiperidinyl-1-oxy

Regioselectivity of Hydroxyl Radical Reactions with Arenes in Nonaqueous Solutions

The regioselectivity of hydroxyl radical addition to arenes was studied using a novel analytical method capable of trapping radicals formed after the first elementary step of reaction, without alteration of the product distributions by secondary oxidation processes. Product analyses of these reactions indicate a preference for o- over p-substitution for electron donating groups, with both favored over m-addition. The observed distributions are qualitatively similar to those observed for the addition of other carbon-centered radicals, although the magnitude of the regioselectivity observed is greater for hydroxyl. The data, reproduced by high accuracy CBS-QB3 computational methods, indicate that both polar and radical stabilization effects play a role in the observed regioselectivities. The application and potential limitations of the analytical method used are discussed.

Aminoxyl-Catalyzed Electrochemical Diazidation of Alkenes Mediated by a Metastable Charge-Transfer Complex

We report the development of a new aminoxyl radical catalyst, CHAMPO, for the electrochemical diazidation of alkenes. Mediated by an anodically generated charge-transfer complex in the form of CHAMPO-N₃, radical diazidation was achieved across a broad scope of alkenes without the need for a transition metal catalyst or a chemical oxidant. Mechanistic data support a dual catalytic role for the aminoxyl serving as both a single-electron oxidant and a radical group transfer agent.

An expeditious entry to 9-azabicyclo[3.3.1]nonane N-oxyl (ABNO): another highly active organocatalyst for oxidation of alcohols

A practical, three-step synthetic route to 9-azabicyclo[3.3.1]nonane N-oxyl (ABNO, 3), an unhindered, stable class of nitroxyl radical, has been developed. ABNO exhibits a highly active nature compared with TEMPO in the catalytic oxidation of alcohols to their corresponding carbonyl compounds.

Rate Constant for the Ring Opening of the 2,2-Difluorocyclopropylcarbinyl Radical

The rate constant for the unimolecular ring opening of the 2,2-difluorocyclopropylcarbinyl radical was determined via its competitive bimolecular trapping by TEMPO. The value of this rate constant (3.4 x 10(11) s(-)(1) at 99.3 degrees C) is about 500 times larger than that of the parent, unfluorinated radical and about 5 times smaller than that of the trans-2-phenylcyclopropylcarbinyl radical.

Polymerization kinetics of resin-based restorative materials

The kinetics and mechanism of cure of resin-based restorative materials have been investigated by incorporating into commercial materials additional amounts of inhibitor, initiator, and accelerator. The polymerization was monitored by IR spectroscopy, viscosity measurements, and an oscillating rheometer. The rate of initiation of the polymerization was found to be first order with respect to the initiator and accelerator concentration. The inhibitor was found to be responsible for the induction period during which no polymerization occurred. The duration of this period was proportional to the inhibitor concentration. It was also found that the efficiency of the inhibitor affected the difference between the initial and final set times so that with one particularly effective inhibitor a "snap-set" behavior could be obtained.