MOLECULAR-STRUCTURE AND CONFORMATIONS OF CYCLONONANE AS STUDIED BY ELECTRON-DIFFRACTION AND MOLECULAR MECHANICS

The structure of cyclononane has been studied by gas-phase electron diffraction at 70°C. An initial guess of the conformational composition was made by using the structures of three conformers generated by molecular mechanics (MM2). Experimental data are shown to be compatible with an existence of a mixture of only two conformers: TCB or [225] (63.5 ± 4.5%) and TBC or [333] (36.5 ± 4.5%). (The [144] conformer is considered to be undetected, as it is formally found to have concentration of 1 ± 12%.) The experimental values with estimated 3σ uncertainties of the geometrical parameters (distances rg, angles ra) are C-C 1.544 (1) Å, C-H 1.119 (3) Å, 〈H-C-H 107.6 (13)° (common to both conformers); for [225] 〈C2-C1-C9 113.6 (8)°, 〈C1-C2-C3 119.3 (19)°, 〈C2-C3-C4 116.2 (19)°, torsional angles τ(C1-C2) -104.5 (14)°, τ(C2-C3) 41.3 (36)°, τ(C1-C9) 94.6 (28)°; for [333] 〈C1-C2-C3 115.3 (10)°, τ(C2-C3) -122.7 (14)°. These results are in satisfactory agreement with the predictions made by molecular mechanics and the available X-ray data and low-temperature NMR work. © 1990 American Chemical Society.