The nitration of p-xylene, mesitylene, naphthalene, [²H₈] naphthalene, durene and some related compounds has been followed by ¹⁵N NMR spectroscopy in a mixture of trifluoroacetic acid and nitro-methane containing sufficient sodium azide to inhibit nitrous acid catalysed nitration. Significant ¹⁵N nuclear polarisation occurs with durene and the naphthalenes and has been analysed by comparison with theoretical curves leading to the calculation of enhancement coefficients. The results indicate that a small part of the reaction of naphthalene with nitronium ions under these conditions involves direct electron transfer between the reactants before the formation of the Wheland intermediate. The extent of this electron transfer is much greater than expected from Marcus theory calculations based on an outer-sphere electron transfer (ET) reaction: the discrepancy is discussed in terms of the initial interaction between the reactants and the solvent effects on the equilibrium constant for the electron transfer.