PHOTOCHEMICAL NITRATION BY TETRANITROMETHANE .11. ISOLATION AND X-RAYSTRUCTURAL-ANALYSIS OF AN ANOMALOUS CIS-1-NITRO 2-TRINITROMETHYL ADDUCT FROM 1,4,5,8-TETRAMETHYLNAPHTHALENE

The photolysis of 1,4,5,8-tetramethylnaphthalene and tetranitromethane in dichloromethane or acetonitrile at -20-degrees-C after long reacti on times gave predominantly products of side-chain nitration, namely 4 ,5,8-trimethyl-1-nitromethylnaphthalene and 4,8-dimethyl-1,5-bis(nitro methyl)naphthalene, the latter a secondary photonitration product of t he former. In addition, two stable adducts were formed resulting from nitro/trinitromethyl addition to 1,4,5,8-tetramethylnaphthalene. In th e beginning of the reactions, labile 1,4-nitrito/trinitromethyl adduct s were detectable, but were transformed into the side-chain nitration product(s) during the course of the reactions. One of the stable adduc ts could be isolated in pure form and was subjected to X-ray crystallo graphic analysis. It was determined to be 1-nitro-c-2-trinitromethyl-1 ,2-dihydronaphthalene, in which the addition mode with the attachment of trinitromethyl at the 2-position and nitro at the 1-position, diffe rs from that of other systems studied. The second stable isomer was sh own by H-1 and C-13 NMR spectroscopy to be the corresponding trans iso mer. The anomalous addition mode could be explained as a consequence o f significantly different steric congestion in the transition states l eading to C1 or C2 attack in the radical cation/trinitromethanide reac tion. The 1,4,5,8-tetramethylnaphthalene radical cation was shown to b e fairly stable chemically under conditions resembling those prevailin g during photolysis, and the system is therefore of interest in being kinetically slow in contrast with most other systems studied previousl y. All reactions must therefore occur between free, solvated species.