The molecular structure of 6, 8, 6 and related systems

Abstract

The crystal structures of 1,2;5,6-dibenzoocta-1,5-diene (1)(C₁₆H₁₆, P2₁/n A= 6.638, B= 6.892, C= 12.625 Å, α= 90.00°, β= 96.58°, γ= 90.00°, Z= 2); 6,7,13,14-tetrahydrodipyrido[1,2-a:1,2-e]diazocinium dibromide (11)(C₁₄H₁₆N₂Br₂·2H₂O, P2₁/n, A= 14.586, B= 6.146, C= 9.159 Å, α= 90.00°, β= 104.16°, γ= 90.00°, Z= 2); 1,2;5,6;9,10-tribenzododeca-1,5,9-triene (12)(C₂₄H₂₄, P2₁/n, A= 19.140, B= 5.122, C= 19.214 Å, α= 90.00°, β= 107.12°, γ= 90.00°, Z= 4) and 1,2;5,6;9,10;13,14-tetrabenzohexadeca-1,5,9,13-tetraene (16)(C₃₂H₃₂, P2₁, A= 12.560, B= 33.665, C= 11.312 Å, α= 90.00°, β= 90.38°, γ= 90.00°, Z= 8) have been determined. The first two, which belong to the 6,8,6 ring system, exist in the solid state in the chair conformation, whereas both the chair and the boat forms are present in solution. The central twelve-membered ring of compound 12 exists in the crystal as an almost perfect C₂ propeller, which is also the only observed conformation in solution. Finally, there are four different molecules of compound 16 in the crystal; however, they roughly correspond to the same conformation (and its enantiomer)[(+–+,–+–,++–,–––) and (–+–,+–+,––+,+++)]. Partial and complementary to literature NMR (¹H and ¹³C) results agree with previous conformational analyses in solution.