Conformational Properties of Ethyl- and 2,2,2-Trifluoroethyl Thionitrites, (CX₃CH₂SNO, X = H and F)

The simple 2,2,2-trifluoroethyl thionitrite molecule, CF₃CH₂SNO, has been prepared in good yield for the first time using CF₃CH₂SH and NOCl in slight excess. The vapor pressure of the red-brown compound CF₃CH₂SNO follows, in the temperature range between 226 and 268 K, the equation log <i>p</i> = 12.0–3881/<i>T</i> (<i>p</i>/bar, <i>T</i>/K), and its extrapolated boiling point reaches 51 °C. Its structural and conformational properties have been compared with the ethyl thionitrite analogue, CH₃CH₂SNO. The FTIR spectra of the vapor of both thionitrites show the presence of bands with well-defined contours, allowing for a detailed conformational analysis and vibrational assignment on the basis of a normal coordinate analysis. The conformational space of both thionitrite derivatives has also been studied by using the DFT and MP2­(full) level of theory with extended basis sets [6-311+G­(2df) and cc-pVTZ]. The overall evaluation of the experimental and theoretical results suggests the existence of a mixture of two conformers at room temperature. The relative abundance of the most stable syn form (NO double bond syn with respect to the C–S single bond) has been estimated to be ca. 79 and 75% for CF₃CH₂SNO and CH₃CH₂SNO, respectively

Matrix Isolation of the Elusive Fluorocarbonylsulfenyl Fluoride Molecule FC(O)SF

The <i>syn</i> and <i>anti</i> conformers of the hitherto unknown fluorocarbonylsulphenyl fluoride FC­(O)­SF were formed through the photochemical reactions between OCS and F₂, isolated in solid Ar. The reactions were followed by Fourier transform infrared (FTIR) spectroscopy, and the unknown products were proposed by comparison of the observed IR absorptions with their computed IR spectra. The reactions occur through a 1:1 molecular complex between OCS and F₂, forming the <i>anti</i>-FC­(O)­SF first, which subsequently transforms into the <i>syn</i> form, through a randomization process. At longer times of irradiation, FC­(O)­SF decomposes by extrusion of a CO molecule with the concomitant formation of SF₂ and the formation of a difluorophosgene molecule, OCF₂. The migration of fluorine atoms in the matrixes is proposed to explain the formation of SF₄ and SF₆

Preparation and Properties of Two Novel Selenoacetic Acids: HCF₂C(O)SeH and ClCF₂C(O)SeH

The novel selenocarboxylic <i>Se</i>-acids, HCF₂C­(O)­SeH and ClCF₂C­(O)­SeH, were prepared by treating the corresponding carboxylic acids with Woollins’ reagent. The boiling points were extrapolated from the vapor pressure curves to be 364 and 359 K for HCF₂C­(O)­SeH and ClCF₂C­(O)­SeH, respectively. Both compounds are unstable at ambient temperatures and decompose to the corresponding seleno anhydrides and release of H₂Se. Hydrolysis results in formation of the carboxylic acids and hydrogen selenide, while diselenides presumably are obtained by oxidation. The conformational properties of these acids were studied by vibrational spectroscopy in combination with ab initio and DFT methods. IR vapor-phase spectra, Raman spectra of the neat liquids, and IR spectra of the Ar-matrix-isolated compounds deposited at two different nozzle temperatures were interpreted in terms of quenching conformational equilibria. The most stable structure of both acids was found to be syn-gauche in equilibrium with a second anti-syn form in HCF₂C­(O)­SeH and with another two conformers, anti-gauche and anti-syn, in ClCF₂C­(O)­SeH

Matrix Isolation Study of the Conformations and Photochemistry of S‑Ethyl Fluorothioformate, FC(O)SCH₂CH₃

The IR spectra of S-ethyl fluorothioformate, FC­(O)­SCH₂CH₃, were recorded in the vapor phase and compared with the Raman spectrum in the liquid state. Additional IR spectra of the compound isolated in argon and nitrogen matrices at ca. 12 K were also recorded. The title compound exhibits rich conformational equilibria at room temperature being <i>C</i>₁ the most stable symmetry with a synperiplanar orientation of the carbonyl double bond (CO) with respect to the S–C­(sp³) single bond, while the C–C bond of the ethyl group presents a gauche orientation with respect to the C–S single bond. Several bands assigned to a second conformer were also observed in the IR matrix spectra. This second rotamer presents a planar skeleton (<i>C</i>_<i>s</i> point group) retaining the prevalent syn orientation of the FC­(O)­SCH₂CH₃ molecule with an antiperiplanar orientation of the C–C bond of the ethyl group with respect to the C–S bond. The variation of the nozzle temperature before matrix gas deposition gives rise to different conformer ratios. With these data an enthalpy difference of 0.45 kcal mol^–1 can be calculated between the more stable <i>C</i>₁ and the <i>C</i>_<i>s</i> conformers. A third form, corresponding to the anti-gauche conformer, is also detected when the matrix is exposed to broad-band UV–visible irradiation. Moreover, the photochemistry of the Ar and N₂ matrix-isolated species is studied. Conformational interconversion is observed at short irradiation times, whereas a decarbonylation process with the concomitant formation of a HC­(S)­CH₃:HF molecular complex dominates the photochemistry of FC­(O)­SCH₂CH₃ of longer irradiation times. The new ethyl fluoro sulfide, FSCH₂CH₃, is proposed as an intermediate species

Chlorodifluoroacetyl Azide, ClF₂CC(O)N₃: Preparation, Properties, and Decomposition

Chlorodifluoroacetyl azide, ClF₂CC­(O)­N₃, was prepared and characterized by IR (gas, Ar matrix), Raman (liquid), UV–vis (gas), and ¹⁹F, ¹³C NMR spectroscopy. The vibrational spectra were analyzed in terms of a single conformer, <i>gauche</i>-<i>syn</i>, where the Cl–C and the N_αN_β bonds are <i>gauche</i> and <i>syn</i> to the CO bond, respectively. The photo and thermal decomposition reactions of the azide were studied with the aid of matrix isolation. In both cases, a new isocyanate species ClF₂CNCO was produced and characterized by matrix IR spectroscopy. The conformational properties and the Curtius rearrangement pathways of this new carbonyl azide were theoretically explored, which suggest the preference of a concerted over stepwise decomposition for the global minimum <i>gauche</i>-<i>syn</i> conformer

Valence and Inner Electronic Excitation, Ionization, and Fragmentation of Perfluoropropionic Acid

The photoexcitation, photoionization, and photofragmentation of gaseous CF₃CF₂C­(O)­OH were studied by means of synchrotron radiation in the valence and inner energy regions. Photofragmentation events were detected from 11.7 eV through formation of COH⁺, C₂F₄⁺, and the parent species M⁺. Because the vertical ionization potential has been reported at 11.94 eV, the starting energy used in this study, 11.7 eV, falls just inside of the tail of the ionization band in the photoelectron spectra. Information from the total ion yield spectra around the C 1s, O 1s, and F 1s ionization potentials allows the energies at which different resonance transitions take place in the molecule to be determined. These transitions have been assigned by comparison with the results of the analysis of similar compounds. In the inner energy region, both kinetic energy release (KER) values and the slope and shape of double coincidence islands obtained from photoelectron–photoion–photoion coincidence (PEPIPICO) spectra allow different photofragmentation mechanisms to be elucidated

Photoexcitation, Photoionization, and Photofragmentantion of CF₃CF₂CF₂C(O)Cl Using Synchrotron Radiation between 13 and 720 eV

The main inner shell ionization edges of gaseous CF₃CF₂CF₂C­(O)­Cl, including Cl 2p, C 1s, O 1s, and F 1s, have been measured in Total Ion Yield (TIY) mode by using tunable synchrotron radiation, and several resonance transitions have been assigned with the help of quantum chemical calculations. Interestingly, resonance transitions observed in the C 1s region can be assigned to different carbon atoms in the molecule according to the degree of fluorine substitution. Ionic photofragmentation processes have been studied by time-of-flight mass spectrometry in the Photoelectron-Photoion-Coincidence (PEPICO) and Photoelectron-Photoion-Photoion-Coincidence (PEPIPICO) modes. These techniques revealed a “memory-lost” effect especially around the C 1s region, since the fragmentation events are independent of the energy range considered. Moreover, different fragmentation mechanisms were inferred from these spectra in the valence (13.0–21.0 eV) as well as in the inner (180.0–750.0 eV) electronic energy regions. The vibrational spectral features of CF₃CF₂CF₂C­(O)Cl have been interpreted in terms of a conformational equilibrium between two conformations (<i>gauche</i> and <i>anti</i> of the CC single bond with respect to the CCl one) at room temperature, as determined from quantum chemical calculations and the detailed analysis of the infrared spectrum