9-DIMETHYLAMINO-9,10-DIHYDRO-9,10-ETHENOANTHRACENE N-OXIDE: AN EXAMPLE WHICH SHOWS SLOW INTERNAL ROTATION ABOUT A Nsp3–Csp3 BOND

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Abstract 9-Dimethylamino-9,10-dihydro-9,10-ethenoanthracene was prepared by reductive dechlorination of its tetrachloro derivative and was oxidized to produce the title compound. The compound crystallized as an ap conformer. On dissolution, it isomerized to its ±sc conformer with a rate constant 2.52×10−5 s−1 at 30 °C until the equilibrium (±sc/ap=0.16) was reached. The following activation parameters were obtained: ΔH≠ 23.1±4.4 kcal mol−1, ΔS≠ −3.9±14.1 e. u.