The molecular structure of 1,3‐diphenylpropane‐1,2,3‐trione (diphenyl triketone) has been determined by gas‐phase electron diffraction at 130°C nozzle temperature. It has been found that the phenyl rings are nearly coplanar with the adjacent carbonyl groups, and the two Cph–C(O)–C(O)–C(O) dihedral angles are ‐ 129.5 ± 0.8 and ‐ 107.1 ± 0.8° (0° corresponds to the syn form). Bond distances (rg, Å) and bond angles (deg) with estimated total errors are CH 1.105 ± 0.006, O C 1.213 ± 0.003, < Cph–Cph> 1.404± 0.003, Cph–C(O) 1.478 ± 0.005, C(O)–C(O) 1.558 ± 0.004, Cph–C(O)–C(O) 120.0 ± 0.3, CphC(O)O 120.8 ± 0.4, C(O)–C(O)–C(O) 117.3 ± 0.4, Cph–Cph(CO)–Cph 119.8 ± 0.6. Although there is a general agreement between the gas‐phase and crystal molecular structures there are some notable differences. One of the benzene rings is slightly turned about the Cph–C(O) axis in the opposite direction in the gas molecule as compared to the crystal. This causes a marked shortening of the O… H intramolecular contact (to 2.18 Á) between the central oxygen and an ortho‐hydrogen.
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