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The relative stabilities of the syn‐ and anti‐conformers of 72 molecules belonging to the XC(W)ZY type, with X, Y = F, Cl, Br and W, Z = O, S, Se, have been computed using the B3LYP/aug‐cc‐pVDZ approximation. The conformational preferences, represented by the energy differences between the two rotamers, exhibit a systematic trend in relation to both the halogen atoms and the chalcogen atoms. These computational predictions are in agreement with available experimental results. The NBO formalism was employed to assess the influence of both the conjugative and anomeric interactions on the relative energy of the conformers. It has been determined that the conjugative interaction provides a satisfactory explanation for the energy differences between rotamers. In contrast, the anomeric interactions favors the syn‐conformation in all cases. The relative stabilities between XC(W)ZY/YC(W)ZX and XC(W)ZY/XC(Z)WY constitutional isomers have also been computed and correlated with the experimental data. [ABSTRACT FROM AUTHOR]

Phenyl and pentafluorophenyl trifluorothioacetate, CF3C(O)SC6H5 and CF3C(O)SC6F5, were prepared by condensation of CF3C(O)Cl and the corresponding mercaptan RSH under vacuum conditions. The compounds were isolated and properly characterized by using infrared spectroscopy, UV-Vis, multinuclear NMR spectroscopy techniques and by mass spectrometry. The crystal structures have been determined for both CF3C(O)SC6H5 and according to the best of our knowledge the not yet reported in the literature CF3C(O)SC6F5 species. The conformational preferences of the three title species were also determined by means of FTIR spectroscopy. In the case of CF3C(O)OC6F5, the FTIR spectrum was also measured in an Ar-matrix and a subsequent photochemical study was performed. The main stable photoproduct found, beside CO, was the ether C6F5OCF3. Quantum-chemical calculations were used to determine the conformational preferences and complement the experimental structure parameters as well as to interpret the UV-Vis spectra determined for the three species under study. As a result of all these experimental determinations complemented with computational calculations, it can be affirmed that the title compounds present a single syn conformation in the analyzed phases (syn with respect to the C＝O double bond and the opposite C–chalcogen single bond). This finding reconfirms the syn conformational transferability found so far for both thioesters and esters, a result that is closely related to the properties of these families in biological processes. [ABSTRACT FROM AUTHOR]

In this work, prereactive complexes, reaction products, and conformational preferences derived from the photochemical reaction between CS2 and ClF were analyzed following the codeposition of the reactants trapped in argon matrices at cryogenic temperatures. After codeposition of CS2 and ClF diluted in Ar, the formation of van der Waals complexes is observed. When the mixture is subsequently irradiated by means of broad-band UV-visible light (225 ≤ λ ≤ 800 nm), fluorothiocarbonylsulfenyl chloride (FC(S)SCl) and chlorothiocarbonylsulfenyl fluoride (ClC(S)SF) are produced. These species exist as two stable planar anti- and syn-conformers (anti- and syn- of the C=S double bond with respect to the S–Cl or S–F single bond, respectively). For both novel molecules, anti-FC(S)SCl and anti-ClC(S)SF are the lowest-energy computed rotamers. As expected due to the photochemical activity of these species, additional reaction products due to alternative or subsequent photochannels are formed during this process. [ABSTRACT FROM AUTHOR]

The reactions of F2 with CS2, SCSe, and CSe2, respectively, were analyzed under matrix conditions by co-deposition of the halogen with the triatomic molecules trapped in argon matrices at cryogenic temperatures. In all cases, after co-deposition, the formation of the respective van der Waals complexes is observed. When each mixture is subsequently irradiated by means of broad-band UV-visible light (200 ≤ λ ≤ 800 nm), FC(S)SF, fluorothiocarbonylsulfenyl fluoride, FC(S)SeF, fluorothiocarbonylselenyl fluoride and FC(Se)SeF, fluoroselenocarbonylselenyl fluoride are produced, respectively. All these species exist as two stable planar syn- and anti-conformers (syn- and anti- of the C＝Z double bond, Y = S, Se, with respect to the S–F or Se–F single bond, respectively). For FC(S)SF, syn- is the rotamer with the lowest energy, while for both FC(S)SeF and FC(Se)SeF the anti-form is the lowest energy conformer. In all cases, other products due to alternative or subsequent photochannels are observed during the photochemical processes carried out in argon matrices at cryogenic temperatures. [ABSTRACT FROM AUTHOR]