Molecular Structure of 7-Oxanorbornane as Studied by Gas Electron Diffraction

The structure of 7-oxabicyclo[2.2.1]heptane (7-oxanorbornane) in the gas phase has been investigated by making joint use of the electron diffraction intensities measured in the present study and the rotational constants reported by Creswell. The thermal average bond lengths are: rg(C1–C2)=1.533±0.014 Å, rg(C2–C3)=1.571±0.015 Å, rg(C–O)=1.442±0.010 Å, and rg(C–H)=1.117±0.008 Å. The bond angles in the zero-point average structure (rav) are: ∠C–O–C=94.5±2.2°, θ (the dihedral angle between the C1–C2–C3–C4 and C4–C5–C–6–C1 planes)=113.5±0.8° and ∠H–C–H=105±5°. The uncertainties represent the estimated limits of experimental error. The C2–C3 bond is longer than the C1–C2 bond, and the latter distance is nearly equal to that of a normal C–C single bond. The C–O bond is about 0.02 Å longer, and the C–O–C bond angle is about 17° smaller than the corresponding parameters in dimethyl ether. These trends are analogous to those observed for norbornane and 7-thianorbornane.