Gas phase structures and conformations of trifluoromethanesulfonyl fluoride, CF 3 SO 2 F, difluoromethanesulfonyl fluoride, CHF 2 SO 2 F, and difluoromethanesulfonyl chloride, CHF 2 SO 2 Cl

Mechanistic and Kinetic Investigations on Decomposition of Trifluoromethanesulfonyl Fluoride in the Presence of Water Vapor and Electric Field

As a potential insulation gas to replace sulfur hexafluoride (SF₆) due to environmental concerns, trifluoromethanesulonyl fluoride (CF₃SO₂F) has attracted great interests in various high-voltage electric applications. Thermal stability of CF₃SO₂F plays an important role in the rational design of the gas-insulated electric equipment. Unimolecular decomposition of CF₃SO₂F was investigated using high-level ab initio methods including the explicitly correlated RCCSD(T)-F12, the composite ROCBS-QB3, and the multireference RS2 extrapolated to complete basis set limit on the basis of M06-2X-, B2PLYPD3-, and CCSD-optimized geometrical parameters. Rate coefficients and decomposition temperatures were simulated using master equations. CF₃SO₂F decomposes predominantly via a simple C-S bond cleavage to form CF₃ and SO₂F, accompanied by a roaming induced F-abstraction detour to release CF₄ and SO₂, or isomerizes via CF₃ migration to the more stable CF₃OSFO followed by the production of CF₂O and SOF₂. Various characteristic decomposition products (e.g., CF₄, C₂F₆, CF₂O, SO₂, SOF₂, SO₂F₂, CF₃H, and so on.) have been identified theoretically through secondary reactions and hydrolysis of CF₃SO₂F in the presence of water vapor. Electronic structures and stability of CF₃SO₂F could be affected significantly by the external electric field orientated along the S-C bond. The field-dependent electron-molecule capture rates support that CF₃SO₂F is superior to SF₆ in dielectric strength. The present computational findings shed light on the practical use of CF₃SO₂F as the replacement gas for SF₆.

Raman spectrum, conformational stability, barriers to internal rotations and DFT calculations of 1,1,1-trifluoro-propane-2-thione with double-internal-symmetric rotor

The Raman spectrum (3500-100 cm-1) of 1,1,1-trifluoro-propane-2-thione (TFPT), CF3C(S)CH3 of the solid phase has been recorded. The internal rotation of CH3 and/or CF3 moieties around CC bonds in TFPT allow five hypothetical conformers (Cs and C1 point groups). Aided by quantum chemical (QC) calculations, the Cc conformer is the only stable form (CF3 and CH3 groups are eclipsing the CS bond) which contains a planar FCC(S)CH backbone and possess intramolecular hydrogen sulfur interactions. However, other conformations (with the orientation of sulfur atom being trans to either hydrogen or fluorine atom) are either transition states or not fully converged geometry with "gauche" orientation. Moreover, the calculation were carried out at the level of Becke three Lee-Yan-Parr (B3LYP) parameters up to 6-311++G(d,p) basis sets. The torsional barriers are adequately described by a three-fold potential, V3 which have been determined utilizing the optimized structural parameters from the B3LYP/6-31G(d) basis set along with potential surface scan. Barriers of 1.28 kcal/mol (448 cm-1) and 1.94 kcal/mol (678 cm-1) were calculated for CH3 and CF3 symmetric rotors, respectively. Complete vibrational assignments have been reported for the stable Cc isomer which is supported by normal coordinate analysis and potential energy distributions (PEDs) for all fundamentals. Moreover, equilibrium geometries, vibrational frequencies are compared to the corresponding experimental values of acetone, 1,1,1-trifluoroacetone (TFA), hexafluoroacetone (HFA) and other molecules having the CF3 moiety whenever appropriate.

Two rotors potential scans and vibrational assignments for dihalomethylsulfonyl isocyanates

The conformational behavior and structural stability of dichloro and difluoromethyl-sulfonyl isocyanates were investigated by quantum mechanical DFT and ab initio calculations. The 6-311 + + G** basis set was employed to include polarization and diffuse functions in the calculation at B3LYP and MP2 levels. The molecules were found to exist in a mixture of trans-gauche and gauche-gauche conformations at ambient temperatures. From the calculations the isocyanate NCO moiety was predicted to nearly eclipse one of the sulfony S=O bonds in the two stable conformers of both molecules. The potential scans for the rotations of the two NCO and CX2H rotors were calculated from which the rotational barriers could be estimated. The vibrational frequencies, potential energy distributions, IR intensities as well as depolarization ratios were calculated.