The radical-annihilator monoid of a ring

Kuratowski’s closure-complement problem gives rise to a monoid generated by the closure and complement operations. Consideration of this monoid yielded an interesting classification of topological spaces, and subsequent decades saw further exploration using other set operations. This article is an exploration of a natural analogue in ring theory: a monoid produced by “radical” and “annihilator” maps on the set of ideals of a ring. We succeed in characterizing semiprime rings and commutative dual rings by their radical-annihilator monoids, and we determine the monoids for commutative local zero-dimensional (in the sense of Krull dimension) rings.     

New photo-responsive unit of biindenylidene with TEMPO radical substituents

Incorporation of organic radical TEMPO into photochromic biindenylidene system leads to the synthesis of a novel dual functional compound 4. Its photochromism, structure, magnetic properties as well as ESR spectroscopy were deliberately investigated. Remarkable changes of the ESR spectra were observed for 4 upon photoirradiation with different light sources. The intermolecular interactions were interpreted with regard to its crystal structure.     

A Chiral Molecular Based Metamagnet Prepared from Manganese Ions and a Chiral Triplet Organic Radical as a Bridging Ligand

Below 5.4 K the one-dimensional polymeric complex made up of manganese(II ) hexafluoroacetylacetonate units and bridging bisaminooxylbenzene diradicals (shown in the picture) behaves as a metamagnet. The R-helical chain not only contains an S-configured chiral carbon center, but also an R-configured C₂-symmetric chiral skeleton of the organic ligand.     

The First Efficient Iodination of Unactivated Aliphatic Hydrocarbons

No heavy metals, no enzymes, and a simple protocol : the direct iodination of aliphatic hydrocarbons, which has not been possible to date, can now be carried out in multiphase systems [see for example Eq. (1)]. In situ generated tetraiodomethane serves as a key intermediate in this selective radical chain reaction initiated by a single electron transfer. This room-temperature, efficient transformation is highly regioselective, easy to work-up, and hence widely applicable.     

p-Benzyne

A noble gas matrix at low temperature was used to investigate the photochemical behavior of diacetyl terephthaloyl diperoxide and dipropionyl terephthaloyl diperoxide as well as 1,4-diiodobenzene. All three photoreactions formed small quantities of a compound with IR absorption bands at 725 and 980 cm⁻¹, which disappeared when the matrix was annealed. These bands correspond to the most intense of the calculated bands (B3LYP) for 1,4-didehydrobenzene (p-benzyne) ( 1 ). That decomposition of the peroxides in fact leads to 1 is confirmed by vapor-phase pyrolysis experiments in which (Z)- 2 was obtained in high yield.     

Overestimation of the stability of the π-delocalized versus the σ-localized configuration in radicals by current density functionals: the case of vinylacyl radicals

 Calculations with the density functional theory (DFT) method using the most popular functional, Becke's three parameter hybrid with the Lee, Yang and Parr correlation functional, predict the π-delocalized configuration of the vinylacyl radical, CH₂=CH—C(•)=O, to be more stable than the σ-localized configuration in contrast with ab initio unrestricted quadratic configuration interaction with single and double excitations calculations as previously found for the isoelectronic vinyl radical, Y-C(•)=CH₂, bearing π-type α substituents. Experimental evidence on the electronic configuration adopted by vinyl radicals is contrasting. In the present case comparison with experiment indicates firmly that the currently available density functionals overestimate the stability of π-delocalized versus σ-localized configurations in radicals since they favor the π configuration for the γ-methylvinylacyl radical, CH₃—CH=CH—C(•)=O, in contrast with unequivocal electron spin resonance data. This failure is mainly due to an incorrect estimate of dynamic correlation energy with DFT functionals. Received: 13 January 2000 / Accepted: 16 March 2000 / Published online: 21 June 2000     

The calculated enthalpies of the nine pyrazole anions, cations, and radicals: a comparison with experiment

Enthalpies of 12 pyrazole species including neutral, anions, cations, and radicals have been calculated at the G3B3 level. The main conclusions are: (i) there are ten equilibria between species of which six have been measured experimentally and the agreement is excellent; (ii) two structures, cyclic and chain, have been found for the pyrazolium-radical 8 that are able to explain the electrochemistry of pyrazolium salts; (iii) the aromaticity, calculated as the NICS indexes, is related to the unexpected stability of the pyrazole anion 3.     

Styrene—Acrylonitrile Copolymerization: Effect of Remote Units on the Reactivity of the Styrene-Ended Radicals

Application of the gas-liquid chromatographic method to the analysis of the process of styrene-acrylonitrile radical copolymerization, especially with a monomer mixture rich in styrene, provided evidence for penultimate and antepenultimate effects. Methods are given for the determination of the corresponding reactivity ratios:

r _A ≈ 0, r _AS = 0.55, r _ASS = 0.50, r _SSS = 0.25     

Optimization of a high‐resolution radical scavenging assay coupled on‐line to reversed‐phase liquid chromatography for antioxidant detection in complex natural extracts

This paper reports the optimization of the on‐line coupling of 2,2′‐azinobis(3‐ethylbenzothiazoline)‐6‐sulfonic acid based radical scavenging assays with reversed‐phase high‐performance liquid chromatography. The residence time in the reactor was reduced to 6.4 s to ensure minimal peak broadening and loss of separation. Peak capacity losses between compound detection and measurement of the radical scavenging potential were reduced to 10% and lower on coupled column systems. The methodology was successfully applied for the detection of the scavenging activity of molecules encompassing a broad hydrophobicity range. The method shows promise for the assessment of low‐molecular‐weight polyphenols in red wine by coupled‐column high‐resolution high‐performance liquid chromatography with mass spectrometry analysis.