Newer aspects of electron transfer in electrophilic Aromatic Nitration. Radical pairs as reactive intermediates by time‐resolved spectroscopy

Aromatic nitration is effectively carried out by the deliberate irradiation of the charge‐transfer absorption band (hvCT) of the transient electron donor–acceptor complex [ArH, NO2Y+], where NO2Y+represents common nitrating agents. Time‐resolved spectroscopy demonstrates that the charge‐transfer nitration effected in this way proceeds via an electron‐transfer mechanism, in which the collapse of the reactive triad, [ArH+ ·, NO , Y] is critical to the formation of the Wheland intermediate. Comparative product analyses of toluene and anisole nitrations together with the ‘non‐conventional’ products arising from NO+catalysis,ipsoattack and addition/elimination show that the activation process leading to charge‐transfer (photochemical) nitration is indistinguishable from that leading to electrophilic (thermal) aromatic nitration.