Photochemical Nitration by Tetranitromethane .XVI. The Regiochemistry of Adduct Formation in the Photochemical Reaction of 1,8-Dimethylnaphthalene and Tetranitromethane; Thermal 1,3-Dipolar Nitro Addition Reactions

Abstract

Photolysis of the 1,8-dimethylnaphthalene/tetranitromethane charge-transfer complex yields the triad of 1,8-dimethylnaphthalene radical cation, nitrogen dioxide, and trinitromethanide ion. In dichloromethane at +20° recombination of this triad gives predominantly the adducts (8), (9), (11), and (14), each of which is formed by attack of the trinitromethanide ion at C4 of the 1,8-dimethylnaphthalene radical cation; a minor adduct (10) is formed by similar attack but at C3 of the aromatic radical cation. The cycloadducts (12) and (13) arise by cycloaddition of the trinitromethyl group to the alkene function in adducts (9) and (14). The cycloaddition (9)→(12) has been shown to be a thermal, not photochemical, reaction. X-Ray crystal structures are reported for adducts (8) and (12).