Photochemical nitration by tetranitromethane. xxix. 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-dihydronaph-thalen-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 C 1 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°, 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.