Bond Alternation in Tropone as Studied by Gas Electron Diffraction

Assuming a planar conformation with C2v symmetry, and using the estimated mean amplitudes of vibration, the bond alternation in tropone was confirmed. The average C–C and C=C distances were determined by the least-squares method to be 1.454±0.010 and 1.362±0.013 Å respectively; moreover, two probable sets of the structure parameters were obtained. On the basis of conformational arguments regarding the structures of related compounds, the following set of the bond lengths was preferred: C–H, 1.098±0.016 Å; C1–O, 1.225±0.012 Å; C1–C2, 1.445±0.012 Å; C2–C3, 1.364±0.012 Å; C3–C4, 1.462±0.012 Å; and C4–C5, 1.342±0.018 Å.