SOLVENT EFFECTS ON THE REACTIVITY OF SOLVATED ELECTRONS WITH IONS IN ISOBUTANOL/WATER MIXED-SOLVENTS

The effective reaction radii kappa R(r), where R(r) is the reactive encounter radius and kappa is the probability of reaction per encounter, for e(s)(-) with H-s(+), NH4,s+, Ag-s(+), Cu-s(2+), and NO3,s- are all 0.7 +/- 0.1 nm in isobutanol containing 10-20 mol% water. The value remains at 0.7 +/- 0.1 nm for H-s(+), Ag-s(+), and Cu-s(2+) in pure isobutanol, and for the two transition metal ions in pure water solvent. The value for NO3,s- reduces to 0.35 nm in pure isobutanol and pure water solvents, whereas for H-s(+) and NH4,s+, in pure water solvent it is only 0.14 nm and 2.6 x 10(-5) nm, respectively. The low reactivity of NH4,s+ with e(s)(-) in water is attributed to the symmetry of the hydrogen-bonded solvation structure of NH4+ in water, and the higher reactivity of H-s(+) (OH3,s+) is attributed to the lower symmetry of its hydrogen-bonded solvation structure. The NH4+ and OH3+ 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(s)(-) in Al(ClO4)(3) solutions in water is due mainly to H-s(+) from hydrolysis of Al-s(3+), and partly to partially hydroxylated aluminum(III) species. Reaction of e(s)(-) with Al-s(3+) itself appears to be negligible in water. The reactivity of the solutions of Al(ClO4)(3) in isobutanol-rich solvents is 3-5 times greater than that in water. In pure C-1 to C-4 1-alcanol solvents the value of k(2)(e(s)(-) + NO3,s-) increases linearly with the dielectric relaxation time tau(1) of the solvent. In these solvents the probability of permanent capture per encounter increases approximately as the square of the encounter duration.