Molecular structure of cyclododecane, C 12H 24, as determined by electron diffraction and molecular mechanics

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The molecular structure of cyclododecane has been studied at 120°C using gas phase electron diffraction assisted by molecular mechanics calculations. Two models suggested earlier by X-ray data have been tested. Electron diffraction data are compatible with a D 4 model while the D 2d model can be rejected, in agreement with molecular mechanics calculations which favor the first model by 10.5 kcal mol −1 over the second. For a model with D 4 symmetry the experimental results give average bond lengths ( r g), independent bond and torsion angles (∠ α) with estimated uncertainties of 3σ. CC 1.540(1) Å, CH 1.114(3) Å, ∠ HCH 104.2(18)°, ∠ C1C2C3 115.0(7)°, τ (C1C2C3C4) 159.5(12)°.