Structural and Conformational Properties of Fluoroformic Acid Anhydride, FC(O)OC(O)F

Abstract

The conformational properties and geometric structures of fluoroformic acid anhydride, FC(O)OC(O)F, have been studied by vibrational spectroscopy, gas electron diffraction (GED), single-crystal X-ray diffraction, and quantum chemical calculations (HF, MP2, and B3LYP methods with 6-31G* and B3LYP/6-311+G* basis sets). Satellite bands in the IR matrix spectra, which increase in intensity when the matrix gas mixture is heated prior to deposition as a matrix, indicate the presence of two conformers at room temperature. According to the electron diffraction analysis, the prevailing conformer is of C(2) symmetry with both C=O bonds synperiplanar with respect to the opposite C-O bond ([sp, sp] conformer). The minor conformer [15(5)% from IR matrix and 6(11)% from GED] is predicted by quantum chemical calculations to possess an [sp, ac] structure. FC(O)OC(O)F crystallizes in the orthorhombic system in the space group P2(1)2(1)2(1) with a = 6.527(1) angstroms, b = 7.027(1) angstroms, and c = 16.191(1) angstroms and four formula units per unit cell. In the crystal, only the [sp, sp] conformer is present, and the structural parameters are very similar to those determined by GED.

Effect of the Substituents on the Nature and Strength of Lone-Pair–Carbonyl Interactions in Acyl Halides

“…We show in Figure an example of crystal structure in which the molecules of fluoroformic acid anhydride (DALJAC) are held together by carbonyl···carbonyl contacts as the only intermolecular interaction. In such a crystal structure, we found O···C contacts as short as 2.81 Å, i.e.…”

“…On the other hand, when the donor is an O atom in the form of a carbonyl group, the approach angle CO•••C is more variable with a random distribution of values between 80 and 180°, in good agreement with previous reports on carbonyl−carbonyl interactions. 13 We show in Figure 2 an example of crystal structure in which the molecules of fluoroformic acid anhydride (DALJAC) 23 are held together by carbonyl•••carbonyl contacts as the only intermolecular interaction. In such a crystal structure, we found O•••C contacts as short as 2.81 Å, i.e.…”

Synthesis and properties of trifluoromethoxyl fluoroformyl anhydride, CF3OC(O)OC(O)F

“…The expected products besides the anhydride are those shown in reactions (9)- (14), which correspond to termination steps:…”

“…The values of n s and n as C5 5O for the s-a-s and s-s-a rotamers (1936-1916 and 1956-1900 cm À1 respectively) are enclosed within the values belonging to the s-s-s rotamer (1968-1886 cm À1 ), so a theoretical analysis of the spectra foresees a relatively wide and noisy asymmetric C5 5O stretching when more than one rotamer is present in the sample. Inspection of the figure in the carbonyl region shows these features in the experimental and simulated [14]. Numbering of atoms follows from Fig.…”

“…Additionally, harmonic vibrational frequencies and zero-point energies (ZPE) were calculated at the same level of theory to check whether the obtained stationary points were either isomers or first-order transition states; the calculated conformers possessed no imaginary frequencies. The determination of the Hessian matrix also enabled calculation of the thermochemical quantities for the conformers at 298.15 K. The selected DFT method has been extensively applied to the determination of geometric parameters of related fluoro-carbon-oxygenated compounds, yielding accurate results tested with gas electron diffraction experiments [13,14,17]. Since we are interested in the minima of the potential energy surface, and DFT methods take into account the electron correlation energy to a partial extent [18], we think that the B3LYP/ 6-311+G* method should be adequate to describe the relative energies for the isomers.…”