The rate constants of the intramolecular electron exchange reaction in the
1,4-dinitrobenzene radical anion in linear alcohols were determined from al
ternating line-broadening effects in EPR spectra. Rate constants at 293 K r
ange from 2.9 x 10(9) s(-1) in methanol to 2.7 x 10(8) s(-1) in octan-1-ol.
The rate constant was found to depend on the reverse of the longitudinal c
orrelation time of the solvent, tau(L), as expected for a solvent-controlle
d adiabatic reaction. Applying Marcus theory and the ellipsoidal cavity mod
el for evaluating lambda(0), the amount of transferred charge between nitro
groups, z, and the outer-sphere reorganisation energy were determined. z c
hanges from 0.56 at 273 K to 0.52 at 313 K. lambda(0) at 293 K changes from
61 kJ mol(-1) in octan-1-ol to 80 kJ mol(-1) in methanol. The activation e
nergies were obtained from the temperature dependence of the rate constants
, changing from 26 kJ mol(-1) in methanol to 36 kJ mol(-1) in octan-1-ol. T
he variation of this energy clearly reflects the increase in the exponentia
l term of z, for the more viscous alcohols. The results for the 1,4-dinitro
benzene radical anion were compared with those previously reported for the
radical anion of 1,3-dinitrobenzene. Rate constants are smaller in the form
er, by three orders of magnitude, due to conjugation of the nitro groups.