5672size and charge distribution. This is supported by measurements of KI for the benzene-p-xylene system over a temperature range of 50" which indicate that AGO and AH" for the equilibrium are essentially the same, suggesting negligible contribution from differences in the entropy effects of solvation. The importance of solvation and ion pairing is, however, being explored more fully despite experimental difficulties attendant on the variation of solvent and cation due to the inherent susceptibility of these radical ions to destructive side reactions.Perhaps the most surprising aspect of our experimental results is the range of more than three orders of magnitude in the values of Kl for the monoalkyl-and p-dialkylbenzenes. The perturbing effect of an alkyl substituent on the electron affinity of benzene may be estimated using molecular orbital theory in a manner such as has been employed successfully for predicting the relative ionization potentials of the alkylbenzenes. l 3 This simple method leads to the prediction that each of the mono-and p-dialkylbenzenes should have the same electron affinity as benzene. This prediction arises simply because the perturbing substituents cannot, to first order, change the energy of the highest filled molecular orbital of the benzene radical anion. l4 Furthermore, this is true for both inductive and hyperconjugative mechanisms of interaction between the alkyl substituent and the aromatic ring. l 4It should also be pointed out that although the apparent relative strengths of the "electron-donating" effects of alkyl groups inferred from our data are in accord with other chemical substituent effects (vide supra), they are opposite the order suggested by the esr hyperfine splittings of the radical anions. For example, of the groups studied, the t-butyl group produces the largest decrease in stability of the benzene radical anion but gives rise to the smallest perturbation of the spin density in the aromatic ring.I5 The esr data and our relative stabilities taken together constitute a significant goal for more refined theoretical treatments of the interaction between saturated and unsaturated groups.Acknowledgments. We wish to thank the National Science Foundation for partial financial support and Professor P. H. Rieger for the generous use of his esr spectrometer. Sir :There are relatively few methods available for the direct substitution of hydrogen in six-membered heteroaromatic nitrogen compounds. Some of the best known are the Tschitschibabin reaction which leads to primary amines and the alkylations and arylations using organolithium compounds.' We now wish to report a new and apparently general method of alkyl and aryl amination of five-and six-membered heteroaromatic nitrogen compounds which complements the Tschitschibabin reaction very nicely.A suitable N-oxide is heated with an imidoyl chloride (or with the corresponding nitrilium salt) in a polar nonprotic solvent. For example, pyridine N-oxide (I, X = Y = H) and N-phenylbenzimidoyl chloride (11, R = R ' = Ph) in boilin...

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