ELECTRON-TRANSFER MECHANISM FOR AROMATIC NITRATION VIA THE PHOTOACTIVATION OF EDA COMPLEXES - DIRECT RELATIONSHIP TO ELECTROPHILIC AROMATIC-SUBSTITUTION

Charge-transfer nitration of various aromatic hydrocarbons (ArH) is re adily achieved by the deliberate photoactivation of their electron don or-acceptor (EDA) complexes with N-nitropyridinium (PyNO2+). Time-reso lved spectroscopy unambiguously identifies (ArH.+, NO2, Py) as the rea ctive triad resulting directly from the charge-transfer activation of the [ArH,PyNO2+] complex; and the subsequent homolytic annihilation of the aromatic cation radical with NO2 leads to the Wheland intermediat e pertinent to aromatic nitration. Charge-transfer nitration of such a romatic donors as toluene, anisole, mesitylene, and tert-butylbenzene as well as the polymethylbenzenes and substituted anisoles forms the b asis for detailed comparisons with the products from electrophilic aro matic nitration, especially with regard to the unique isomer distribut ions, nuclear versus side-chain nitrations, and ipso adducts in noncon ventional nitrations. Mechanistic implications are discussed in terms of the electron-transfer activation of electrophilic aromatic nitratio n.