Reinvestigation of the Molecular Structure of 1,3,5,7-Cyclooctatetraene by Electron Diffraction

The molecular structure of 1,3,5,7‐cyclooctatetraene has been studied by a sector‐microphotometer technique using data extending to very much larger scattering angles than were obtained in earlier investigations. An application of the method of least squares to sector‐microphotometer data in electron diffraction worked out by one of us (KH) has led in three refinement stages to unusually precise values for the parameters. The following are the more interesting parameter values with standard errors. It should be noted these results do not include a possible error of up to 0.2% in the scale of the molecule because of uncertainties in the electron wavelength, nor do they include the effect of correlations among the observations on the standard errors, which we estimate might increase the standard errors by as much as the factor 2^½. Molecular symmetry $D_{\text{2d}},\mathrm{C}=\mathrm{C}\text{=1.334±0.001\hspace{0.17em}}\mathrm{A},\mathrm{C}–\mathrm{C}\text{=1.462±0.001\hspace{0.17em}}\mathrm{A},\mathrm{C}–\mathrm{H}\text{=1.090±0.005\hspace{0.17em}}\mathrm{A}\mathrm{,\angle }\mathrm{C}=\mathrm{C}–\mathrm{C}{\text{=126.46}}^{\circ }{\text{±0.23}}^{\circ }\mathrm{,\angle }\mathrm{C}=\mathrm{C}–\mathrm{H}{\text{=118.3}}^{\circ }{\text{±5.9}}^{\circ }{\mathrm{,a}}_{\mathrm{C}=\mathrm{C}}{\mathrm{(=〈\delta l}}^2{〉}_{\mathrm{C}=\mathrm{C}}{\text{/2)=(103±7)×10}}^{\text{−5}}{\mathrm{,a}}_{\mathrm{C}–\mathrm{C}}{\text{=(147±10)×10}}^{\text{−5}}{\mathrm{,a}}_{{\mathrm{C}}_1\mathrm{···}{\mathrm{C}}_3}{\text{=(256±13)×10}}^{\text{−5}}{\mathrm{,\hspace{0.17em}a}}_{{\mathrm{C}}_1\mathrm{···}{\mathrm{C}}_4}{\text{=(530±100)×10}}^{\text{−5}}{\mathrm{,\hspace{0.17em}a}}_{\mathrm{C}–\mathrm{H}}{\text{=(327±36)×10}}^{\text{−5}}{\mathrm{,\hspace{0.17em}a}}_{{\mathrm{C}}_2\mathrm{···}\mathrm{H}}{\text{=(520±110)×10}}^{\text{−5}}{\mathrm{,a}}_{{\mathrm{C}}_3\mathrm{···}\mathrm{H}}{\text{=(640±180)×10}}^{\text{−5}}$ .