Iminoxy radicals

Ellinger155 and co-workers have obtained ab initio electrostatic molecular potential maps158 for the iminoxy radical H2CNO in investigations of the electrophilic reactivity in nitroxides, using a small basis set. Attack at the nitrogen lone pair is favoured in this molecule. 

The rate of oxidation of acetophenoximes with bismuth(V) fluoride in a mixture of hydrogen fluoride and perchloric acid follows first-order kinetics in both the oxime and Bi(V). The reaction is acid catalysed. A bridged outer-sphere mechanism, involving formation of an iminoxy radical, has been suggested.81... 

The electronic structures of these imino radicals are particularly interesting as they are ir-radicals as compared to the 6-iminoxy radicals RR C=N-0. Prom the... 

One of the factors that may contribute to fewer studies of 6-radicals is their higher reactivity. For example, the hydrocarbon 6-radicals are more reactive than the ir-radicals, and the phenyl radical has never been observed by ESR in the liquid phase. Similarly, iminoxy radicals are much less stable than nitroxide ir-radicals, and Norman, Gilbert, and coworkers have studied extensively some of the 6-iminoxy radicals by the use of flow techniques (261-263). This difference in reactivity was explained (138) by the fact that in 6-radicals the unpaired electron is located in a directional sp-orbital which projects away from the neighboring atoms, resulting in reduced repulsion between the radical and the reacting molecule in the activated complex. 

The reaction of metal diketonates with NO (x = 1, 2) has been reported . NO2 reacts with substituted M(acac) derivatives of Fe(III), Mn(II) and Cu(II) affording the iminoxy radical 111. The radicals presumably are formed after decomposition of the chelate complex, in view of the fact that the EPR parameters of the free radical are not influenced by the metal ion and that the same radical is also obtained by reaction of the corresponding free ligand and N02 . 

On the basis of an EPR analysis, the reaction of M(acac) with NO2 (at room temperature it is present as N2O4) has been proposed to occur via a step-by-step oxidation of the metal complex with final formation of metal nitrates and the iminoxy free radical 111 (equation 79). The presence of a donor-acceptor complex between M(acac) and N2O4 has been postulated for the electron transfer to dinitrogen tetroxide. 

The life-times of iminoxy radicals in solution vary quite widely with structure (Gilbert and Norman, 1966a). When lead tetra-acetate is used as the oxidant, other e.s.r. spectra are also observed (Lown, 1966a). For example, when acetoxime is oxidized, the spectrum (Fig. 4) of the... 

The nitrogen-splittings in iminoxy radicals, R R C=N—O, are 30 G, which is very much larger than in nitroxides and probably reflects the fact that there is a significant spin density at nitrogen in an... 

An e.s.r. study has been made of the reaction of N02 with metal acetylacetonates. Those complexes of metals which have stable lower oxidation states (i.e. Cu , Fem, Co111, and VO11) react to form iminoxy radicals, while those metals which are not readily reduced (e.g. Zn11, Crra, and Cem) do not give iminoxy radicals.116... 

Foirmation of nitroxide and iminoxy radicals is enhanced by ultraviolet radiation. This indicates that the photochemical dissociation of NO2 into nitric oxide and oxygen atoms plays an important role in the reaction with double bonds. 

Further Roumanian work is reported on the e.s.r. of iminoxy-radicals obtained from oximes with bicyclo[3,3,l]nonane and bicyclo[3,2,l]octane skeletons substituted in the 2- and 4-positions. The introduction of a bulky substituent in the exo-2-or exo,exo-2,4-positions in the [3,3,1] skeleton leads to a preference for a chair-boat conformation whereas endo-2-, endo,endo-2,4-, or en io,exo-2,4-substituents produce the chair-chair conformation. 

In their article on RHC=NO iminoxy radicals Berski et used a topological analysis of ELF supplemented with AIM. It was shown that Z to E isomerization resulted in a redistribution of electron density from the N and O lone electron pairs to the N-0 and C=N bonds. The AIM analysis of E isomeric forms showed quite the same trends for both charge and spin reorganization within the atomic basins. 

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