Reinvestigation of the molecular structure of gaseous p-benzoquinone by electron diffraction

The molecular structure of gaseous p‐benzoquinone has been studied by electron diffraction at a nozzle‐tip temperature of 110–125°C. The molecule has D_2h symmetry to within experimental error. The results for the more important distance (r_a), bond angle, and rms amplitude (l) parameters are $r_{\mathrm{C–H}}\text{=1.089\hspace{0.17em}}\mathrm{\AA }{\text{\hspace{0.17em}(0.011),\hspace{0.17em}r}}_{\mathrm{C=O}}\text{=1.225\hspace{0.17em}}\mathrm{\AA }{\text{\hspace{0.17em}(0.002),\hspace{0.17em}r}}_{\mathrm{C=C}}\text{=1.344\hspace{0.17em}}\mathrm{\AA }{\text{\hspace{0.17em}(0.003),\hspace{0.17em}r}}_{\mathrm{C–C}}\text{=1.481\hspace{0.17em}}\mathrm{\AA }\text{\hspace{0.17em}(0.002),\hspace{0.17em}∠}{\mathrm{C}}_2{\mathrm{C}}_1{\mathrm{C}}_6\text{=118.1°\hspace{0.17em}(0.3),\hspace{0.17em}∠}{\mathrm{C}}_3{\mathrm{C}}_2\mathrm{H}\text{=121.4°\hspace{0.17em}(}\mathrm{assumed}{\mathrm{),\hspace{0.17em}l}}_{\mathrm{C–H}}\text{=0.077\hspace{0.17em}}\mathrm{\AA }\mathrm{\hspace{0.17em}(}\mathrm{assumed}{\mathrm{),\hspace{0.17em}l}}_{\mathrm{C=O}}\text{=0.0424\hspace{0.17em}}\mathrm{\AA }{\text{\hspace{0.17em}(0.0020),\hspace{0.17em}l}}_{\mathrm{C=C}}\text{=0.0446\hspace{0.17em}}\mathrm{\AA }\text{\hspace{0.17em}(0.0024)}$ , and $l_{\mathrm{C–C}}\text{=0.0546\hspace{0.17em}}\mathrm{\AA }\text{\hspace{0.17em}(0.0024)}$ . These values are in good agreement with those found in an early electron‐diffraction study by Swingle, and except for the length of the carbon‐carbon double bond, in excellent agreement with those found in the crystal by Trotter.