Valency

About: Valency is a research topic. Over the lifetime, 1632 publications have been published within this topic receiving 26141 citations.

"Wandering" valency in organophosphorus free radicals

Abstract: Phosphorus—contain.ing radicals of the type P')where OO stands or phen1enedioxi group, are desc?ibed. The new radicals have been generated bi photoche— mical addition of o—quinones to phosphorus or b' photoreac-.. tions o: o—quinones with b1rogen spirophoaphoranea. Oxda— tion of corresponding o-.oxyspirophosphoranea with Pb02 leads to the same radicals. The ESR spectra of the radicals ob-. tamed show a characteristic temperature dependence. per— fine splittings observed at low temperatures correspond to unpaired electron interactions with protons of only one aro— matic ring, whereas at higher temperatures, protons of two or all the three aromatic uganda are involved. In the latter case, the radical has an octahedral symmetry on the ESR time scale, and the unpaired electron \"wanders\" over six oxygen atoms (\"wandering valency\"). The number of o:xygen atoms participating in spin delocalization may be lower than 6 depending on the radical structure. The phenomenon described is a new type of phosphorotropic tautomerism. Temperature—dependent variations of the ESR spectra studied include characteristic linewidth alternations which have been used to calculate exchange frequencies. A possible mechanism of valency wandering is discussed. New radicals have been generated by reduction of phosphors— te anions containing hexacoordinate phosphorus. Salts con-. taming these anions have been prepared from ortho—quinones and phosphorus in high yields. The properties of the new compounds are described. The wandering valency phenomenon has also been observed with radicals containing other than phosphorus elements, such as boron, aluminium, silicon, arsenic, etc. • Temperature van— atious of ESR spectra of these radicals have been studied. By analogy with ionotropic tautomerism,we use the term tautoxnerism of free radicals to describe their spontaneous and reversible isomerization: One of the possible isomerization mechanisms is free valency and bond transfer within the radical: x-1x • The process should be regarded as intramolecular radical substitution at X. With Symmetrical radicals (R is identical to R'), the equilibrium is degenerate Which implies a double—well potential with two minima of the same depth. The group X undergoing migration may be hydrogen. Aurik and Stork were the first to observe such radical H—tropy as degenerate tautomerism of iminol radical (I) in 1972 [11. Somewhat later we have studied phenoyl radical (II) and its tautomerism [21.