1-Hydropyridinyl radicals

Hydropyridinyl radicals ESR, 2, 145 Hydroquinoline synthesis, 1, 441 Hydroquinones synthesis, 1, 417 of-Hydroxy acids dehydrogenation by flavins, 1, 253... 

Azine anion-radicals are highly basic and undergo N-protonation in the presence of proton sources. The resultant neutral 1-hydropyridinyl radicals are discussed subsequently (Section III,A,2). 

Hydropyridinyl radicals have given excellently resolved ESR spectra which have been assigned following MO calculations and partial deuteration experiments. Experimental results from various workers are compared in Table III for a series of C-monosubstituted 1-hydropyridinyl radicals. 

There has been intensive study of 1-hydropyridinyl radicals bearing one or more carboxylic acid substituents.72,195,198-202 In basic solution these radicals are anionic, but the charge is associated with the ionization of the acid functions and not with the radical moiety. Equilibrium and kinetic data have been reported for the acid ionizations 198-202 and the variation of persistence with structure discussed.195... 

Hayon and co-workers have studied, by pulse radiolysis, 1-hydropyridinyl radicals ranging from those formed from simple C-acylpyridines to those from pyridoxine and pyridoxal phosphate.210-212 Structural, spectroscopic, kinetic, and thermodynamic data have been presented. Various mechanisms have been adduced which involve 35 and analogous species from quinolines,... 

Experimental Hyperfine Splittings (in Gauss) for Monosubstituted 1-Hydropyridinyl Radicals ... 

Soviet workers have reported hydrazyl radicals such as 210 and 1-alkyl-1-hydropyridinyl radicals containing benzothiazolyl or... 

In the absence of a 4-substituent, 1-alkyl-l-hydropyridinyl radicals dimerize rapidly. Simple 1-alkyl-l-hydropyridinyls, generated electrochemi-cally from the corresponding pyridinium salts, form 1,1 -dialkyl-1,1, 4,4 -tetrahydro-4,4 -bipyridines which are oxidized at the prevailing potential to dialkylviologen cation-radicals which form the final product (Scheme 2 X = H, route abed).230... 

Many 1-alkyl-l-hydropyridinyl radicals are not persistent in aqueous medium. The bimolecular decay reaction has been investigated for 66 and 70 and a mechanism consistent with products and kinetics advanced.239 The reactions of 70, its 3-carboxamide isomer, and the pyridinyl radical derived from nicotinamide adenine dinucleotide (NAD) with cytochrome c have been investigated by pulse radiolysis and rates established.240... 

Reactions of simple pyridines with bis(trimethylsilyl)mercury results in the formation of l,r-bis(trimethylsilyl)-l,l, 4,4 -tetrahydro-4,4 -bipyridines. These reversibly dissociate on heating in oxygen-free solution to yield 1-trimethylsilyl-l-hydropyridinyl radicals which have been characterized by ESR, e.g., 71 for which splittings are given in gauss.241 If the pyridines bear... 

Chemical and physical evidence has been obtained for the mediation of 1-acyl-l-hydropyridinyl radicals in the complex suite of react ions which ensues on thermolysis of l,l -diacyl-1,1, 4,4 -tetrahydro-4,4 -bipyridines.243,244... 

The radicals obtained upon reduction of pyridine dicarboxylic acids in liquid ammonia proved to have 1-hydropyridinyl structures, e.g., 49.72 These are treated with similar species in Section III,A,2. 

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