Solvent Structure Effects and Diffusion Control in the Reaction Between Solvated Electrons and Solvated Protons in Alcohols and Water

Jha, K.N.; Bolton, Gerald L.; Freeman, Gordon R.

doi:10.1139/v72-487

Cited by 3 publications

(1 citation statement)

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“… Entropy changes are usually considered responsible for the very negative values of d(Δ G °/d T ) in reactions of solvated electrons. They are thought to arise from a large number of states available to the electron in a disordered liquid, or in terms of the structure-breaking nature of the solvated electron − and related concepts . Negative entropy changes might also arise because reaction 1 combines two species into one.…”

Section: Discussionmentioning

confidence: 99%

Benzene Radical Ion in Equilibrium with Solvated Electrons

2003

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Radical anions of benzene (C 6 H 6 ) and its monofluoro and -methyl derivatives are found to exist in equilibrium with solvated electrons in THF solution. At 298 K C 6 H 6 •is less stable than the solvated electron with K eq ) 0.22 M -1 , but at lower temperatures C 6 H 6 •is favored, K eq reaching 65 M -1 at 218 K. The energetics (∆H°)-26 kJ/mol; ∆S°) -101 J/deg mol) are remarkable because the same reaction is endoergic by 1.17 eV in the gas phase. For fluorobenzene, K eq )1.7 × 10 2 M -1 at 298 K and is also strongly temperature-dependent with a similar, large negative entropy change (∆H°) -49 kJ/mol; ∆S°) -121 J/deg mol). The energetics can be understood by taking into account a substantial (∼1 eV) electronic energy of the solvated electron. The large apparent "entropy changes" may include changes that are not entropic, but arise instead from temperature and density dependent enthalpy changes. The optical absorption spectrum of C 6 H 6 •is similar to that reported at 77 K. As would be expected for an ion of small size, C 6 H 6 •forms strongly bound ion pairs with Na + ; the dissociation constant for (C 6 H 6 •-,Na + ) ion pairs is 4.5 × 10 -10 M. This strong ion pairing stabilizes C 6 H 6 •when a counterion is available, explaining why the ion-pair, but not the free ion of benzene, is readily observed.

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