Photochemical nitration by tetranitromethane .29. Adduct formation in the photochemical reaction of tetranitromethane and 1,5-dimethylnaphthalene; Allylic rearrangements of adducts

Photolysis of the 1,5-dimethylnaphthalene/tetranitromethane charge-transfer complex yields the triad of 1,5-dimethylnaphthalene radical cation, nitrogen dioxide and trinitromethanide ion. Recombination of this triad gives predominantly the epimeric 4,8-dimethyl-1-nitro-4-trinitromethyl-1,4-dihydronaphthalenes (18) and (27), the epimeric 1,5-dimethyl-1-nitro-4-trinitromethyl-1,4-dihydronaphthalenes (20) and (21), 4,8-dimethyl-r-1-nitro-t-2-trinitromethyl-1,2-dihydronaphthalene (19), 4,8-dimethyl-t-2-trinitromethyl-1,2-dihydronaphthalen -r-1-ol (23), nitro cycloadduct (22), hydroxy cycloadduct (24), nitronic ester (25) and 4,8-dimethyl-1-nitronaphthalene (26). Adduct (19) is formed substantially by allylic rearrangement of 4,8-dimethyl-1-nitro-4-trinitromethyl-1,4-dihydronaphthalene (18), and adduct (23) and indirectly nitronic ester (25) by allylic rearrangement of a postulated intermediate 4,8-dimethyl-t-4-trinitromethyl-1,4-dihydronaphthalen-r-1-ol. (32). Adducts (18), (19), (23), (25) and (27) are formed by attack of trinitromethanide ion at C1 of the 1,5-dimethylnaphthalene radical cation, while adducts (20)-(22) and (24) are formed by the corresponding attack at C4, the reaction pathways being determined by the relative energies of the intermediate delocalized carbon radicals. Adduct formation is substantially suppressed for a photolysis when trifluoroacetic acid (0.7 M) is added to the dichloromethane solvent at 20 degrees, 1,5-dimethyl-4-nitronaphthalene (26) being formed close to quantitatively. In contrast, photolysis of the 1,5-dimethylnaphthalene/tetranitromethane charge-transfer complex in 1,1,1,3,3,3-hexafluoropropan-2-ol gave substantial amounts of adduct (19), together with 1,5-dimethyl-4-nitronaphthalene (26) as the major product. Allylic rearrangements of 1-methoxy-4-nitro-1-trinitromethyl-1,4-dihydronaphthalene (34) and the epimeric 1,4,5,8-tetramethyl-1-nitro-4-trinitromethyl-1,4-dihydronaphthalenes (38) are seen as the mode of formation of 4-methoxy-r-1-nitro-t-2-trinitromethyl-1,2-dihydronaphthalene (33) and the epimeric 1,4,5,8-tetramethyl- 1-nitro-2-trinitromethyl-1,2-dihydronaphthalenes (36), respectively. X-Ray crystal structure determinations are reported for adducts (19), (20), (22), (24) and (28), the last compound being formed only on chromatography of reaction mixtures.