PHOTOCHEMICAL NITRATION BY TETRANITROMETHANE .11. ISOLATION AND X-RAY STRUCTURAL-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 reaction times gave predominantly products of side-chain nitration, namely 4,5,8-trimethyl-1-nitromethylnaphthalene and 4,8-dimethyl-1,5-bis(nitromethyl)naphthalene, the latter a secondary photonitration product of the former. In addition, two stable adducts were formed resulting from nitro/trinitromethyl addition to 1,4,5,8-tetramethylnaphthalene. In the beginning of the reactions, labile 1,4-nitrito/trinitromethyl adducts were detectable, but were transformed into the side-chain nitration product(s) during the course of the reactions. One of the stable adducts could be isolated in pure form and was subjected to X-ray crystallographic analysis. It was determined to be 1,4,5,8-tetramethyl-r-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, differs from that of other systems studied. The second stable isomer was shown by H-1 and C-13 NMR spectroscopy to be the corresponding trans isomer. The anomalous addition mode could be explained as a consequence of significantly different steric congestion in the transition states leading to C1 or C2 attack in the radical cation/trinitromethanide reaction. The 1,4,5,8-tetramethylnaphthalene radical cation was shown to be fairly stable chemically under conditions resembling those prevailing during photolysis, and the system is therefore of interest in being kinetically slow in contrast with most other systems studied previously. All reactions must therefore occur between free, solvated species.