Molecular structure of 3,4-difluorofuran-2,5-dione (difluoromaleic anhydride) as determined by electron diffraction and microwave spectroscopy in thegas phase and by theoretical computations

The structure of 3,4-difluorofuran-2,5-dione has been determined experiment ally in the gas phase by microwave spectroscopy using rotation constants de rived from five isotopomers and by a combined analysis of electron-diffract ion and microwave data. The geometry is planar with C-2v symmetry. Structur al parameters [distances (r(alpha)degrees)/pm, angles angle(alpha)/deg, (1 sigma errors)] for the combined analysis are: r(C=O) = 119.0(1); r(C-F) = 1 30.9(2); r-(C=C) = 133.2(3), r(O-C) = 139.3(1); r(C-C) = 148.5(2); angle C- C=C = 108.3(1); angle C=C-F = 129.9(1); angle C-C=O = 129.3(1); angle C-O-C = 108.9(1); angle O-C-C = 107.2(1). These values are in excellent agreemen t with those obtained in an ab initio study of the molecular geometry at th e MP2/6-311+G*(2df) level of theory. The dipole moment of difluoromaleic an hydride has been determined experimentally by Stark-effect measurements to be 1.867(3) D.