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 irradi ation of the charge-transfer absorption band (hnu(CT)) of the transien t 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 el ectron-transfer mechanism, in which the collapse of the reactive triad , [ArH+., NO2., Y] is critical to the formation of the Wheland interme diate. Comparative product analyses of toluene and anisole nitrations together with the 'non-conventional' products arising from NO+ catalys is, ipso attack and addition/elimination show that the activation proc ess leading to charge-transfer (photochemical) nitration is indistingu ishable from that leading to electrophilic (thermal) aromatic nitratio n.