The molecular structure of gaseous tetrafluoro-p-benzoquinone and tetramethyl-p-benzoquinone as determined by electron diffraction

The molecular structures of gaseous tetrafluoro-p-benzoquinone (p-fluoranil) and tetramethyl-p-benzoquinone (duroquinone) have been investigated by electron diffraction. Except for the methyl group hydrogen atoms, the molecules are planar to within experimental error, but small deviations from planarity are completely compatible with the data. Values for the geometrical parameters (r_adistances and r_α with parenthesized uncertainties of 2σ including estimated uncertainty in the electron wavelength and correlation effects, are as follows. Tetrafluoro-p-benzoquinone: D_2h symmetry (assumed); r(C0) = 1.211(6) Å, r(CC) = 1.339(12) Å, r(C-C) = 1.489(5') Å, r(C-F) = 1.323(5) Å, ∠C-C-C = 116.8(7)° and ∠C-C-F = 116.1(7)°. Tetramethyl-p-benzoquinone: C_2h symmetry (assumed);r(C-H) = 1.102(18) Å, r(CO) = 1.229(8) Å, r(CC) = 1.352(8) Å, r(C_sp2-C_sp2) = 1.491(11) Å, r(C_sp2-C_sp3) = 1.504(12) A, ∠C-CO-C = 120.8(8)°. ∠C-C-CH₃ = 116.1(8)°, ∠C-C-H = 110.5(34)° and α₁ = α₂ (methyl torsion = 30° (assumed).