Nitroxide radicals. Part XVI. Unpaired electron distribution in para-substituted aryl t-butyl nitroxides and 2-naphthyl phenyl nitroxides

Strongest Ferromagnetic Coupling in Designed Gadolinium(III)–Nitroxide Coordination Compounds

“…The spin density was evaluated from the ESR hyperfine splitting constants (hfsc), which are also in proportion to the spin density. The typical nitrogen hfsc values are 1.2 ± 0.2 mT for aryl tert -butyl nitroxides , and 0.74 ± 0.03 mT for nitronyl nitroxides. , The spin density at the nitroxide oxygen atom is assumed to be proportional to that of the nitrogen atom. Alternatively, polarized neutron diffraction studies may also be helpful to clarify the spin distribution in the solid state.…”

Nitroxide radicals. Part 21. Spontaneous decomposition of N-aryl 1- and 2-naphthyl nitroxides

“…Under these conditions the nitroxide (2c) underwent no appreciable change. The others gave significant amounts of 1 ,4naphthoquinone imine (7) and secondary amine ( 5 ) accompanied by a large number of minor coloured products which were not isolated. Two additional products the benzoquinone imine (4e) and its N-oxide (3e) were isolated from the nitroxide (2e).…”

“…Although naphthoquinone imine N-oxides (6) are not major decomposition products it is possible that they are formed as intermediates en route to the naphthoquinone imines (7). To test this possibility a series of 1,4-naphthoquinone imine N- * Benzoquinone imine (4d) and benzoquinone imine N-oxide (3d) also produced.…”

“…A similar oxidation of the only benzoquinone imine (4e) isolated gave the corresponding benzoquinone imine N-oxide (3e) thus providing confirmation of structure. The quinone imines (7) and their N-oxides ( 6) are easily distinguished spectroscopically since the introduction of the oxygen onto the nitrogen causes a downfield shift of the peri-8H (8.3 +9.6), a lowering of vmX. (C=N, C=O) by 5-20 cm-l, and a bathochromic shift of the long wavelength band in the u.v./visible region (33M390 nm) (see Table 2).…”

“…Similarly when the nitroxide (2c) and an excess of amine (5a) were allowed to react the amine (5c) and the quinone imine (7a) were formed. Hence, the quinone imines (7) are formed from the corresponding amines ( 5 ) by (a) hydrogen abstraction by the nitroxide (2) followed by coupling of a second molecule of nitroxide at the C-4 naphthyl position of the phenyl naphthylaminyl formed in step (a) and fragmentation of the intermediate. The hydroxylamine (1) formed in step (a) would undergo spontaneous aerial oxidation giving more nitroxide.…”