Effect of Isotopic Substitution upon the Gas Phase and Solution Electron Affinities of Nitrobenzene

Article abstract of DOI:10.1021/ja00247a005

Ion cyclotron resonance and electron spin resonance have been utilized to determine the equilibrium constant for the electron transfer from the nitrobenzene anion radical to ¹⁵N labeled nitrobenzene (Ph¹⁴NO2^.- + Ph¹⁵NO2 <-> Ph¹⁴NO2 + Ph¹⁵NO2^.-).It was found that the equilibrium constant is within experimental error of unity at 305 K.Molecular orbital calculations indicate that this might be accounted for by the shortening of the C-N bond and a counterbalancing lengthening of the N-O bonds upon electron attachment to nitrobenzene.An equilibrium constant that is much larger than unity can be observed in liquid ammonia at 208 K when K⁺ serves as a gegenion (K_eq=2.1).However, when Na⁺ serves as a gegenion, the solution electron affinity of Ph¹⁴NO2 is greater than that of Ph¹⁵NO2 (K_eq=0.4).These results are explained in terms of ion association.When the hydrogen atoms are replaced with deuteriums, the gas phase electron affinity is decreased.A similar decrease is observed in liquid ammonia.In the gas phase this is attributed to the slight lengthening of all the C-H bonds upon electron attachment.