Electron spin resonance in American coals

Electron spin resonance of sedimentary humic acids in relation to their aromatic character

“…If free radicals in a sedimentary humic acid are in the form of simple semiquinone type, their g values must be similar to those of known semiquinones, such as 1, 4-benzosemiquinone (2.0047), 2-methyl 1,4-benzosemiquinone (2.0046), 1,4-naphthosemiquinone (2.0044) and ,9,10-anthrasemiquinone (2.0041) (BLOIS et al, 1961). The g values of a soil humic acid (2.005 5: KLEIST and MUCKE, 1966), peat and lignite (2.0040 2.0055: RETCOFSKY et al, 1968) are in good agreement with those of known semiquinone radicals. But g values of the sedimentary humic acids examined here are inconsistent with those of known semiquinone radicals.…”

“…Semiquinone radical. has been inferred to be present in soil humic acids (STEELINK, 1964(STEELINK, , 1966ATHERTON etal., 1967;SCHNITZER and SKINNER, 1969), lignite and peat (RETCOFSKY et al, 1968). If free radicals in a sedimentary humic acid are in the form of simple semiquinone type, their g values must be similar to those of known semiquinones, such as 1, 4-benzosemiquinone (2.0047), 2-methyl 1,4-benzosemiquinone (2.0046), 1,4-naphthosemiquinone (2.0044) and ,9,10-anthrasemiquinone (2.0041) (BLOIS et al, 1961).…”

Molecular study of insoluble organic matter in Kainsaz CO3 carbonaceous chondrite: Comparison with CI and CM IOM

“…The deviation of the g value from the free electron value g e = 2.0023 is due to the spin-orbit interaction experienced by the unpaired electrons of the radicals. Therefore, as shown by EPR investigations on terrestrial IOM such as coals (Retcofsky et al 1968), this interaction in carbonaceous radicals is enhanced when the wave functions of the unpaired electrons are delocalized over heteroelements, so that the deviation increases when the heteroelement content increases. Among the most common heteroelements, oxygen and nitrogen, oxygen has a stronger effect due to its stronger intrinsic spin-orbit interaction.…”

Caracterização de adubos orgânicos por espectroscopia de ressonância paramagnética eletrônica

“…Uma possibilidade para a estrutura referente ao sinal do RLO é de semiquinonas possivelmente conjugadas a anéis aromáticos (Schnitzer & Skinner, 1969;Riffaldi & Schnitzer, 1972;Senesi & Steelink, 1989;Senesi, 1990;Stevenson, 1994), nas quais o elétron desemparelhado possui maior probabilidade de estar sobre o átomo de oxigênio. No caso do carvão vegetal, devido à sua estrutura química característica, pode ocorrer maior deslocalização do elétron desemparelhado, fazendo com que o valor do fator g seja menor (Retcofsky et al, 1968;Schnitzer & Skinner, 1969). A figura 6b mostra que a adição do carvão vegetal à amostra 7 ocasionou diminuição do valor do fator g da amostra de adubo orgânico, sendo isso perceptível com baixas porcentagens de carvão adicionado.…”