RUZHONG CHEN, YURIS AVOTINSH, and GORDON R. FREEMAN. Can. J. Chem. 72, 1083 (1994.The effective reaction radii a,, where R, is the reactive encounter radius and K is the probability of reaction per encounter, for e; with H: , NH,',,, Ag:, Cu?, and NOT, are all 0.7 f 0.1 nm in isobutanol containing 1G20 mol% water. The value remains at 0.7 f 0.1 nm for H: , Ag:, and Cu? in pure isobutanol, and for the two transition metal ions in pure water solvent.The value for NO;, reduces to 0.35 nm in pure isobutanol and pure water solvents, whereas for H: and NH;, in pure water solvent it is only 0.14 nm and 2.6 x nm, respectively. The low reactivity of NH,',, with e; in water is attributed to the symmetry of the hydrogen-bonded solvation structure of NH; in water, and the higher reactivity of H: (OH;,,) is attributed to the lower symmetry of its hydrogen-bonded solvation structure. The NH,' and OH; ions have no low-lying orbital for an electron to occupy, so either reaction occurs by proton transfer to the electron site or the neutral species must decompose. We suggest that the proton transfer or the decomposition of the neutral species is facilitated by an unsymmetrical solvation structure.Reaction of e; in A1(C104)3 solutions in water is due mainly to H: from hydrolysis of Alp, and partly to partially hydroxylated aluminum(II1) species. Reaction of e; with A12 itself appears to be negligible in water. The reactivity of the solutions of Al(C104)3 in isobutanol-rich solvents is 3-5 times greater than that in water.In pure CI to C4 1-alcanol solvents the value of k2(e; +NO,,) increases linearly with the dielectric relaxation time z, of the solvent. In these solvents the probability of permanent capture per encounter increases approximately as the square of the encounter duration. On attribue la faible rCactivitC du NH,',, avec les e; dans l'eau i la symCtrie de la structure de solvatation comportant des liaisons hydrogknes du NH,',, dans l'eau et on attribue la rCactivitC plus ClevCe des H: (OH;,) B la symCtrie plus faible de sa structure de solvatation comportant une liaison hydrogkne. Les ions NH; et OH; n'ont aucune orbitale de bas niveau pour accommoder un Clectron; la rkaction se produit donc par un transfert de proton vers un site dlClectron ou les espkces neutres doivent se dicomposer. On suggkre que le transfert de proton ou la dCcomposition d'espkces neutres est rendu plus facile par une structure de solvatation qui n'est pas symttrique.La rCaction des e; dans des solutions de A1(C104)3 dans l'eau est principalement due aux H: provenant de l'hydrolyse

RUZHONG CHEN and GORDON R. FREEMAN. Can. J. Chem. 71, 1303 (1993). Values of the rate constants, k2 (lo6 m h o l -I s-'), of solvated electrons, e,, with several related salts, in pure water and pure I-butanol solvents at 298 K are, respectively, as follows: LiNO,, 9.2, 0.19; NH4N03,10, 8.3; NH4C1O4, 1.5 x 12 in 20 mol% water; LiCIO,, 1.0 x lo-" < I . O x lo-'. The value of k2(e, + NO3.,-) in water solvent is 48 times larger than that in 1-butanol solvent, whereas k2(e,L + NH4,,+) in water is times smaller than the value in I-butanol. This enormous reversal of solvent effects on e, reaction rates is the first observed for ionic reactants. The solvent participates chemically in the (e, + NO,,,-) reaction, and the overall rate constant increases with irzcreasirzg viscosity and dielectric relaxation time. This unusual behavior is attributed to a greatly increased probability of reaction of an encounter pair with increasing duration of the encounter. Effective reaction radii KR, for (e; + and (e, + NH,.,') were estimated with the aid of measured electrical conductances of the salt solutions in all the solvents. Values of KR, are (2-7) x lo-'' m, except for NH4,,+ in 100 and 99 mol% water, which are 2.6 and 2.7 X 10-l4 m, respectively. The effective radii of the ions for mutual diffusion increase with increasing butanol content of the solvent, from -50 pm in water to -150 pm in 1-butanol, due to the increasing average size of the molecules that solvate the ions. La valeur de k,(e, + NO,,,-) dans l'eau est 48 fois plus forte que dans le 1-butanol comme solvant; par ailleurs, la valeur de k2(e,L + NH,,,') dans l'eau est lo-' fois plus faible que dans le I-butanol comme solvant. Cet Cnorme difference des effets de solvant sur les vitesses de reaction des e, est la premiere a &tre observee avec des reactifs ioniques. Le solvant participe chimiquement dans la reaction de (e, + NO3,,-) et la constante globale de vitesse augmente avec une augmentation de la viscosite et du temps de relaxation dielectrique. On attribue ce comportement inhabituel ii une grande augmentation de la probabilite de reaction d'une paire de rencontre avec une augmentation de la durte de la rencontre. Faisant appel a des mesures de conductances Clectriques des solutions de sels dans tous les solvants, on a Cvaluk les rayons efficaces de reaction, KR,, des reactions (e, + NO,,,-) et (e, + NH,,,'). Les valeurs de KR, s'etalent de 2 i 7 X lo-" m, except6 pour le NH,,,+ dans les solutions contenant 99 ou 100 mol% d'eau alors que les valeurs sont respectivement de 2,7 et 2,6 x l~-~~ m. De -50 pm en eau a -150 pm en I-butanol, les rayons efficaces des ions pour la diffusion mutuelle augmentent avec une augmentation de la concentration de butanol dans le solvant; ce resultat est cause par une augmentation de la grosseur moyenne des mol~cules qui solvatent les ions.[Traduit par la redaction]

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10) Kaneko, F.; Kobayashi, M.; Kitagawa, Y.; Matsuura, Y. Acta (11) Holland, R. F.; Nielsen, J. R. (15) Ungar, G.; Keller, A. Colloid Polym. Sci. 1979, 257, 95. (16) Zerbi, G.; Piazza, R.; Holland-Moritz, K. Polymer 1982, 23, 1921. (17) Zerbi, G.; Magni, R.; Gussoni, M.; Moriz, K. H.; Bigotto, A.; Dir-(18) Organ, S. J.; Keller, A. The recent suggestion (J. Phys. Chem. 1991,95,897) that the ion-pair association constant of ammonium nitrate in methanol is K2 >> 10 m3/mol ( lo4 M-I) at about 293 K would have interesting implications for our embryonic understanding of solvent effects, if it were correct. Electrical conductance measurements of solutions at concentrations from 1 to 995 mol/" demonstrate that ammonium nitrate behaves as a normal, strong electrolyte in methanol. The conductances are fitted by the Onsager-Fuoss equation, the second term of which contributes the greatest reduction in conductance and corresponds to the ion-atmosphere (long-range interactions) model of Milner, Debye, and Hackel. A new attack on the theory of concentrated electrolyte solutions should be made by computer simulation.(1) Duplltre, G.; Jonah, C. D. J. Phys. Chem. 1991, 95, 897. (2) Atkins. P. W. Physicol Chemistry, 4th ed.; Freeman: New York, 1990; (3) Weast, R. C. Hondbook of Chemistry ond Physics, 70th ed.; CRC (4) Conway, B. E. Electrochemicol Doto; Elsevier: Amsterdam, 1952; pp p 760-1 (note that B requires p).The cyclohexane/polyoxyethylene(4)nonylphenol (E0(4)NP)/water system (2.8% EO(4)NP) with [H20] 1 [EO(4)NP] molar ratios between 0.1 and 6.9, has been investigated by electron spin resonance (ESR) spectroscopy using the following nitroxides: 3-carboxy-2,2,5,5-tetramethylpyrroIine-lsxyl (I), 2,5-dihydr~2,2,5,5-tetramethyl-3-[(triethylammonio)methyl]pyrrole-1-oxy1 bromide (11), and 5-doxylstearic acid (IV) as spin probes. For radicals I and I1 the nitrogen hyperfine splitting, aN, and the rotational correlation time, T~, have been analyzed, yielding information about the polarity and viscosity of their locations.At [H20]/[EO(4)NP] 6 0.3, the presence of "waterless" micellar aggregates in fast exchange (v, > 106 s-') with the monomer surfactant is evident. At [H20]/[EO(4)NP] = 0.6, the core viscoSity is at its maximum value and the exchange rate decreases below the limit of slow exchange (vex < lo6 s-I). Upon further increasing the water content, the core becomes more polar and less viscous, with these parameters approaching their values in bulk water. The effect of Cu(I1) ion (in an oil-soluble complex) on the spectra of radical II-confined to the water-pool-has been interpreted by using Leigh's theory, and the 'distance of closest approach" between these two paramagnetic species has been evaluated. This distance is considered to represent a measure of the penetrability of the micellar shell. Radical IV yielded anisotropic spectra in the aggregates with slow exchange. From their ESR parameters the order degree of the surfactant chains in the micellar shell has been evaluated. All results are consistent, indicating reduced ...