Rosana M. Romano

N-Sulfinylimine compounds, R–NSO: a chemistry family with strong temperament

Abstract In this review, an update on the structural properties and theoretical studies of N -sulfinylimine compounds (R–NSO) is reported. They were deduced using several experimental techniques: gas–electron diffraction (GED), X-ray diffraction, 17 O NMR, ultraviolet-visible absorption spectroscopy (UV–Vis), FTIR (including matrix studies of molecular randomisation) and Raman (including pre-resonant Raman spectra). Data are compared with those obtained by theoretical calculations. With these tools, excited state geometry using the time-dependent theory was calculated for these kinds of compounds. The existence of pre-resonant Raman effect was reported recently for R–NSO compounds. The configuration of R–NSO compounds was checked for this series confirming the existence of only one syn configuration. This finding is corroborated by theoretical calculations. The method of preparation is also summarised.

S-ethyl thiochloroformate, ClC(O)SCH2CH3: Unusual conformational properties?

Abstract The conformational equilibrium of S-ethyl thiochloroformate, ClC(O)SCH2CH3, was determined by vibrational spectroscopy (FTIR and FTRaman spectra), ab initio and density functional theory calculations (HF/3-21G*, HF/6-31G* and B3PW91/6-31G*). The evaluation of experimental and theoretical results suggests the existence of two conformers syn, gauche (CO double bond syn with respect to the S–C single bond and C–S single bond gauche with respect to the C–C single bond, respectively) and syn, anti, being the former most stable one. The existence of this rotational isomerism is rather unexpected for this thioester compound, owing to the known conformational equilibrium reported for some thioesters that depends on the ClCSC torsion angle. Photolysis products of the compound irradiated in adequate inert gas matrices were identified as CO, SCO, C2H5SCl and C2H5Cl.

VIBRATIONAL STUDIES OF FLUOROFORMYLIMINOSULFUR DIFLUORIDE : FC(O)NSF2

Abstract The Raman spectrum of liquid fluoroformyliminosulfur difluoride. FC(O)NSF2, and its IR spectrum of the vapor phase were obtained. The observed features and the polarized Raman spectra are consistent with the existence of only one conformer possessing Cs symmetry both in the vapor and liquid phases. Assignment of 13 of the 15 fundamental vibrations are reported. The UV-visible spectrum was recorded and its bands assigned. The preresonance Raman effect was not detected. A theoretical ab initio vibrational spectrum was also obtained using a 6-31G∗ basis set. Symmetry force constants arising from experimental data were determined for the A′ species.

Selenoacetic Acid, CH3C(O)SeH: Preparation, Characterization, and Conformational Properties

Selenocarboxylic acids (RC(O)SeH) and their derivatives have experienced growing interest during the last two decades. Some synthetic contributions to aliphatic (R = CnHm with n 2) and aromatic selenocarboxylic acids have been made by Kato et al. In contrast, carboxylic acids (RC(O)OH) and thiocarboxylic acids (RC(O)SH) are common compounds with a wide range of applications. Thioacetic acid, CH3C(O)SH, was first reported in 1854 by Kekule; however, the seleno analogue, CH3C(O)SeH, has been neither isolated nor characterized hitherto. Herein, we describe the preparation of selenoacetic acid in its normal form and in its perdeuterated form, CD3C(O)SeD. We also report its low-temperature single-crystal structure, its physical properties, its vibrational, UV/Vis, and NMR spectra, and its photochemical behavior in matrix isolation. CH3C(O)SeH and CD3C(O)SeD are formed within one day by treatment of CH3C(O)OH or CD3C(O)OD, respectively, with an excess of Woollins reagent, Ph2P2Se4, [10] at 75 8C in a small pyrex vessel under moistureand air-free conditions. The progress of the reaction was followed by recording gas-phase FTIR spectra of small samples of the reaction mixture. After 3 hours, a new set of bands (at 1758, 1362, 1110, 1006, 953, and 575 cm 1 in the reaction with CH3C(O)OH; and at 1751, 1131, 975, and 522 cm 1 in the reaction with CD3C(O)OD) became visible in the IR spectrum of the reaction mixture. The reaction mixture was separated by repeated trap-to-trap fractional condensation in vacuum, and the pure product was retained at 90 8C. In similar earlier studies, Knapp and Darout proposed the intermediate formation of selenocarboxylic acids by treating Woollins reagent with RC(O)OH, but they did not isolate the compounds. CH3C(O)SeH and CD3C(O)SeD are shiny green liquids at room temperature with a fetid odor characteristic of toxic organoselenium compounds. For CH3C(O)SeH, the melting point is 223 K, and the vapor pressure over the temperature range 248–291 K follows the equation lnp = 10.78 4111/T (p [atm]; T [K]), giving an extrapolated normal boiling point of 382 K (see Figures S1 and S2 in the Supporting Information). The melting and boiling points of CH3C(O)SeH are lower than those of CH3C(O)OH (290 and 391 K) because of the much weaker hydrogen bonding in selenoacetic acid. In the presence of air, selenoacetic acid is immediately oxidized to the corresponding yellow diselenide CH3C(O)Se2C(O)CH3. Hydrolysis of selenoacetic acid results in the instantaneous formation of acetic acid and hydrogen selenide. Selenoacetic acid is thermally stable at room temperature in a sealed glass vessel for several hours. Theoretical calculations on selenoacetic acid predict the syn form to be more stable than the anti form (Figure 1), with an energy difference of 0.67 or 0.94 kcalmol 1 at the B3LYP/ 6-311 + + G**and MP2/6-311 + + G** levels of theory, respectively (Table S1 and Figure S3 in the Supporting Information). Gas-phase acidity calculations predict that selenoacetic acid is the strongest acid of the series CH3C(O)EH (E = O, S, Se), followed by thioacetic acid, and acetic acid (Table S2).

A solid state study of the configuration and conformation of OSN–R (R=C6H5 and C6H3(CH3–CH2)2-2,6)

Abstract The X-ray crystal structures for N-sulfinyl-benzenamine (OSN–C 6 H 5 ) and N-sulfinyl-2,6-diethyl benzenamine (OSN–C 6 H 3 (CH 3 –CH 2 ) 2 -2,6) are reported. For OSN–C 6 H 5 a planar structure with syn configuration of the OSN–R group was determined. For OSN–C 6 H 3 (CH 3 –CH 2 ) 2 -2,6 this configuration was maintained, however, the spacial requirements of the substituents in the ortho position affect the planarity of the molecule. The OSN group is rotated by 55.3° from the planar structure. Ab initio calculations predict the most stable structures for both compounds.

Perchloromethyl Mercaptan, CCl3SCl, Excited with Synchrotron Radiation in the Proximity of the Sulfur and Chlorine 2p Edges: Dissociative Photoionization of Highly Halogenated Species

We have investigated the dissociative photoionization of shallow-core excited CCl3SCl by using multicoincidence time-of-flight mass spectrometry and synchrotron radiation in the S 2p and Cl 2p edges. The relative abundances of the ionic fragments and their kinetic energy release values were obtained from both PEPICO (photoelectron photoion coincidence) and PEPIPICO (photoelectron photoion photoion coincidence) spectra. The dynamic of the ionic fragmentation of S and Cl 2p excited CCl3SCl has been studied and compared with those of CCl4. Features determined in the present study seem to be relevant aspects for explaining the dissociation of highly chlorinated species under the action of VUV irradiation. The fragmentation pattern shows that chlorine ion (Cl+) is prominently formed upon both S and Cl 2p excitations.

He I Photoelectron Spectra and Valence Synchrotron Photoionization for XC(O)SCl (X = F, Cl) Compounds

Small penta-atomic molecules like FC(O)SCl and ClC(O)SCl have been analyzed by using both photoelectron spectroscopy (PES) and results derived from the use of synchrotron radiation in the same energy range. For this second experiment total ion yield (TIY), photoelectron photoion coincidence (PEPICO), and partial ion yield (PIY) spectra have been recorded. This set of data together with results obtained by computational chemistry allow us to study electronic properties and the ionization channels of both species. Thus, whereas the photodissociation behavior of FC(O)SCl can be divided into three well-defined energy regions, the fragmentation dynamics of ClC(O)SCl seems to be more complex. Nevertheless, simultaneous evaluation of the PES and valence synchrotron photoionization studies helps to clarify the molecular ionization processes.

Dissociative photoionization of methyl thiocyanate, CH3SCN, in the proximity of the sulfur 2p edge.

The dissociative photoionization of gaseous CH3SCN has been investigated at the S 2p core level using time-of-flight mass spectrometry and synchrotron radiation. The total ion yield spectrum could be successfully assigned by comparison with available data from electron energy loss spectra. The relative abundances of the ionic fragments and their kinetic energy release values were obtained from both PEPICO (photoelectron photoion coincidence) and PEPIPICO (photoelectron photoion photoion coincidence) spectra. The dynamics of the ionic fragmentation of S 2p excited CH3SCN is dominated by the rupture of both carbon-sulfur bonds. This process may be related with electronic excitations from the ground electronic state to vacant sigma* molecular orbitals.

HeI Photoelectron and Valence Synchrotron Photoionization Studies of the Thioester Molecule CH3C(O)SCH3: Evidence of Vibronic Structure

One of the simplest thioester molecules, S-methyl thioacetate, CH 3C(O)SCH 3, has been investigated by HeI photoelectron spectroscopy (PES) and valence photoionization studies using synchrotron radiation in the same energy range. In the second series of experiments, total ion yield (TIY), photoelectron photoion coincidence (PEPICO), and partial ion yield (PIY) spectra were recorded. It was found that the photodissociation behavior of CH 3C(O)SCH 3 can be divided into three well-defined energy regions. Vibronic structure was observed in the valence synchrotron photoionization process, being associated with wavenumbers of 912, 671, 1288, 1690, and 1409 cm (-1) for the bands at 12.82, 13.27, 15.66, 15.72, and 17.42 eV, respectively. Evaluation of the PE spectrum in concert with the synchrotron photoionization measurements and complemented by high-level ab initio calculations thus provides unusually detailed insights into the valence ionization processes of this molecule.

Vibrational spectra and theoretical calculations of N-(trifluoromethyl)iminosulphur dichloride: CF3NSCl2

Abstract The Raman spectrum of liquid N -(trifluoromethyl)iminosulphur dichloride, CF 3 NSCl 2 and the infrared spectrum of its vapour phase were recorded. The observed features were consistent with the existence of only one conformer with Cs symmetry, as derived by the reported electron-diffraction analysis. Theoretical vibrational spectra were also determined using ab initio and Density Functional Theory (DFT) calculations at different levels of approximation. For all except one of the torsional modes, experimental wavenumbers were obtained. A subsequent normal coordinate analysis was performed using a torsional wavenumber calculated by theoretical methods.