Photochemical nitration by tetranitromethane part XXXI. The photochemical reaction of 1,2,3,4-tetramethylbenzene and tetranitromethane

Photolysis of the 1,2,3,4-tetramethylbenzene-tetranitromethane charge-transfer complex yields the triad of 1,2,3,4-tetramethylbenzene radical cation, nitrogen dioxide and trinitromethanide ion. Recombination of this triad gives predominantly the epimeric 1,2,3,4-tetramethyl-3-nitro-6-trinitromethylcyclohexa-1,4-dienes 8 and 9, 1,2,3,4-tetramethyl-r-5-nitro-t-6-trinitromethylcyclohexa-1,3-diene (10) and its nitro-alkene cycloaddition product, nitro cycloadduct 11, the 'double adduct' 1,2,3,4-tetramethyl- c-2,c-5-dinitro-t-6-trinitromethylcyclohex-3-en-r-1-ol 12, 2,3,4,5-tetramethyl-1-nitrobenzene (13), and the two products of elimination or rearrangement of labile intermediate adducts, 2,3,4,5-tetramethyl-1-trinitromethylbenzene (7) and 2,3,4-trimethyl-1-nitromethylbenzene (14). Adducts 8-12, and 2,3,4,5-tetramethyl-1-trinitromethylbenzene (7) are formed by initial attack of trinitromethanide ion at a non-methylated ring position in the radical cation of 1,2,3,4-tetramethylbenzene (6), while 2,3,4-trimethyl-1-nitromethylbenzene (14) arises from initial attack of trinitromethanide ion ipso to a 1-(4-)-methyl group in the radical cation 6 ⁺ . Adduct formation is substantially suppressed in the photolysis of the 1,2,3,4-tetramethylbenzene-tetranitromethane charge-transfer complex in 1,1,1,3,3,3-hexafluoro-2-propanol, only the adduct elimination product 2,3,4,5-tetramethyl-1-trinitromethylbenzene (7) being formed in addition to the major product, 2,3,4,5-tetramethyl-1-nitrobenzene (13). X-Ray crystal structure determinations are reported for 2,3,4,5-tetramethyl-1-trinitromethylbenzene (7) and adduct 9.