An electron diffraction study of the molecular structure of gaseous bicyclo[3.3.1]nonane

Abstract

A gas-phase electron diffraction study of the title compound, carried out at 65°C, has found no statistically significant evidence for the presence of any conformer other than the double chair. The geometrical parameters were found to be: r g(CC) av = 1.538(1) Å, r g(CH) av = 1.116(3) Å, ∠C1C9C5 = 111.5(1.1)°, ∠C2C3C4 = 111.2(1.4)°, ∠HCH = 107.0(2.6)°, ∠θ = 121.5(0.8)°, ∠ϕ = 42.6(2.5)°. In an attempt to refine electron diffraction data for models with three non-equivalent CC distances, two sets of molecular parameters were obtained. Amplitudes of vibration were calculated from an approximate force field and the uncertainties in the fixed amplitudes were analyzed. The resulting structural parameters, chosen on the basis of molecular mechanical calculations, were: ( r g structure for bond lengths, r α structure for angles) C1C2 = 1.559(10) Å, C2C3 = 1.541(10) Å, C1C9 = 1.480(9) Å, CH = 1.114(3) Å, ∠C1C9C5 = 110.1(2.3)°, ∠C2C3C4 = 113.2(2.7)°, ∠HCH = 111.4(3.5)°, ∠θ = 124.1(0.9), ∠ϕ = 40.0(2.0)°. Comparison with structures of other bicyclo[ n.m.1]alkanes has been made.