Linewidth alternation, as a result of intramolecular cation migration, in the electron spin resonance spectrum of the 1,4-naphthoquinone radical anion

Abstract

The radical anion of 1,4-naphthoquinone has been prepared by electrochemical reduction in dimethylformamide and by alkali-metal reduction in 1,2-dimethoxyethane. The e.s.r. spectrum of the radical anion in dimethylformamide can be readily interpreted in terms of three pairs of equivalent protons. However, in 1 ,Zdimethoxyethane, association of the alkali-metal counter-ion with one of the carbonyl groups removes the equivalence within each of these pairs. Linewidth alternation is observed in the e.s.r. spectrum when either Na+, K+ or Cs+ is the counter-ion as a result of intramolecular cation migration between equivalent sites adjacent to the two carbonyl groups. The rate of migration varies in the sequence Cs+ > K+ > Na+ > Li+, indicating that Li+ interacts more strongly with the radical anion than (say) Cs+. The disruption of the spin distribution within the radical anion, which is also greatest when Li+ is the counter-ion, supports this conclusion. ~~ ~ T/K 42-H) 43-H) 45-H) 46-H) 47-H) 48-H) ~/ 1 0 -~ s

Tannic Acid Radicals in the Presence of Alkali Metal Salts and Their Impact on the Formation of Silicate-Phenolic Networks

“… 39 Further, the potential binding to TA hydroxyl reaction sites 23 and the high stability of ionic (O - ···Li + ) complexes may cause irreversible Li + complexes with phenolic structures. 40 , 41 This effect is for example encountered in lithiation of the solid-state interface in energy storage materials. 42 Regarding interactions between Li + and Si aq , an interaction preventing the assembly of silicate-TA networks may also be plausible, but evidence of any reactions under the conditions of this study were not found in literature.…”

“…This can be explained by influences in charge densities caused by the cation. 34 , 41 All salts produced lower intensities for ⧫- and ◊-radicals ( Figure S16 ). At pH 9, this effect was however canceled by Si aq for NaCl and LiCl ( Figure S16 ), which suggests a radical stabilizing effect similar to Zn 2+ .…”

“…While radical parameters of both ⧫- and ◊-radicals in NaCl and KCl solution did not differ from their corresponding signals without salt, LiCl appeared to slightly reduce the HFC constant compared to solutions without salt. This can be explained by influences in charge densities caused by the cation. , All salts produced lower intensities for ⧫- and ◊-radicals (Figure S16). At pH 9, this effect was however canceled by Si aq for NaCl and LiCl (Figure S16), which suggests a radical stabilizing effect similar to Zn 2+ . , …”

Pressure effects on cation migration in 2,5‐di‐tert‐butyl‐1,4‐benzoquinone radical anion

“…Using a well-established method [3,4], spectral simulation involving the two-site jumping of cations was performed [ Fig. 1(1 ]), suggesting some effect caused by intermolecular jumping of the cation.…”

“…EPR studies of semiquinone radical anions have provided information about electron transfers, but they have been even more informative about cation migration between two sites. Until now, discussion of the mechanism of cation migration in 1,4-naphthoquinone and 2,5-di-tert-butyl-1,4-benzoquinone radical anions has been based on the EPR studies [3,4]. However, the detailed mechanism of cation migration has not yet been established.…”