Dimers of Perhaloacetyl Cyanides: CClF₂C(O)OC(CN)₂CClF₂ and CF₃C(O)OC(CN) ₂CF₃. Preparation, Properties, and Spectroscopy

The vapor of the new compound 1,1-dicyano-2-chloro-2,2-difluoroethyl chlorodifluoroacetate, CClF₂C­(O)­OC­(CN)₂CClF₂ and of the known 1,1-dicyano-2,2,2-trifluoroethyl trifluoroacetate, CF₃C­(O)­OC­(CN)₂CF₃, were investigated using vibrational spectroscopy tools. The existence of rotational isomerism was confirmed for CClF₂C­(O)­OC­(CN)₂CClF₂ when the matrix isolated compound was examined in combination with the computational results applying quantum chemical models. From the four conformers <i>gauche-syn-gauche, gauche-syn-anti, syn-syn-anti, syn-syn-gauche</i> (the used nomenclature is with respect to the ϕ­(ClC–C­(O)), ϕ­((O)­C-OC), and ϕ­(OC–CCl) torsion angles, respectively) predicted for CClF₂C­(O)­OC­(CN)₂CClF₂ the first two forms can be evidenced using Ar-matrix IR spectroscopy, with the first one being the most abundant at room temperature. On the other side, the results obtained for CF₃C­(O)­OC­(CN)₂CF₃ reveals the existence of only one <i>syn-syn-anti</i> form. CClF₂C­(O)­OC­(CN)₂CClF₂ melts at −40 °C and its vapor pressure was fitted by the equation ln p = −4732.6 (1/<i>T</i>) + 10.75 (<i>p</i> [Atm], <i>T</i> [K]) in the range −20 to 20 °C. Its extrapolated boiling point is 167 °C. The first ionization potentials occur for CClF₂C­(O)­OC­(CN)₂CClF₂ and CF₃C­(O)­OC­(CN)₂CF₃ at 12.13 and 12.43 eV, respectively, and were attributed to the ejection of electrons formally located at the carbonylic oxygen lone-pair electrons (<i>n</i>_O). The proposed interpretation of the photoelectron spectrum is consistent with related molecules reported previously, and also with the prediction of Outer Valence Green’s Functions (OVGF)