The structure of chloromethyl thiocyanate, CH2ClSCN, in gas and crystalline phases.

The structural and conformational properties of chloromethyl thiocyanate, CH2ClSCN, were studied in the solid phase and in the gas phase using in situ low-temperature single-crystal X-ray diffraction experiments (XRD) and gas electron diffraction (GED), respectively. Depending on the mutual orientation of the Cl-C bond and the -SCN group, two conformations, gauche and anti, were found to coexist in the gas phase. The gauche conformer, with a dihedral angle φ(ClC-SC) = 71.8(4)°, is the most stable form, with an abundance of 89(3)% at ambient temperature. High level quantum-chemical calculations at the CCSD(T)/cc-pVTZ level of approximation reproduce these experimental results. In the solid state only gauche conformers were found to be present. The crystal structure shows specific intermolecular interactions including chalcogen-type interactions. The experimental electron density distribution was determined by high-angle X-ray diffraction. The atoms in molecules (AIM) theory was applied to analyze the charge density topology for a better characterization of intermolecular interactions present in the crystal.

Vibrational and theoretical studies of N-(fluorosulfonyl)imidosulfurous difluoride, FSO2N=SF2.

The Raman spectrum of liquid N-(fluorosulfonyl)imidosulfurous difluoride FSO2N = SF2 and the IR spectrum of its vapour phase were recorded. The observed features in combination with the theoretical studies indicate the existence at room temperature of only one conformer. In accord with previous results obtained by electron-diffraction analysis, this single conformer possesses C1 symmetry in which the SF2 group is oriented syn with respect to the N-S single bond. 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.

Tautomers and conformers of malonamide, NH2-C(O)-CH2-C(O)-NH2: vibrational analysis, NMR spectra and ab initio calculations.

The conformational and tautomeric compositions of malonamide, NH2-C(O)-CH2-C(O)-NH2 were determined by vibrational spectroscopy and theoretical calculations (HF/6-31G*, B3PW91/6-31G*). Solid state Fourier transform infrared and Raman spectra were analysed. They reveal the existence of a diketo tautomer. Theoretical calculations predict a diketo structure belonging to the C1 symmetry group. No enol form is present in the molecule in the solid. 13C-NMR studies show only signals of a diketo tautomer.

Preparation and conformational properties of the perfluoro diether CF(3)OCF(2)OCF(2)C(O)F, a model molecule to study properties of perfluoro polyethers.

The compound CF(3)OCF(2)OCF(2)C(O)F was prepared by oxidation of hexafluoropropene with molecular oxygen in the gas-phase using CF(3)OF as initiator. (13)C NMR, FTIR, Raman, UV-vis, and mass spectra were obtained and interpreted. The theoretical structure studies were performed by the calculation of the potential energy surfaces, using the results obtained for a smaller related molecule, CF(3)OCF(2)C(O)F, as a starting point. A high degree of conformational flexibility of this compound is evidenced by the values of several conformations, varying within the range of 1 kcal/mol. Theoretical calculations predict chain conformations as the most stable molecular forms, as expected from the presence of the anomeric effect. The experimental fundamental vibrational modes are compared with those obtained theoretically, using ab initio and density functional theory methods, HF/6-31+G and B3LYP/6-31+G, respectively. The density of the compound at ambient temperature (delta = 1.7(1) g/mL), its melting point (mp = -140(5) degrees C), its boiling point (bp = 14.5 (1) degrees C), and the relation between its vapor pressure and the absolute temperature (ln P = 13.699 - 2023.4/T) were also determined.

Structure and conformational properties of diacetyl sulfide in the gaseous and condensed phases explored by gas electron diffraction, single-crystal X-ray diffraction, vibrational spectroscopy, and quantum chemical calculations.

On the evidence of the electron diffraction pattern of the vapor, of the IR spectrum of the matrix-isolated molecule, and of quantum chemical calculations, the diacetyl sulfide molecule, CH3C(O)SC(O)CH3, adopts a planar heavy-atom skeleton with the [sp,ap] conformation. Other conformations contribute little (<1%) to the population of the gaseous molecules at normal temperatures. Salient structural parameters (r(a) structure, distances (in A), angles (in deg), and 3sigma uncertainties in parentheses) were as follows: r(C=O) 1.198(2)/1.196(2), r(C-S) 1.787(3)/1.808(3), r(C-C) 1.483(4)/1.472(4), angleC-S-C 108.8(9), angleS-C=O 125.7(6)/115.1(6), and angleS-C-C 121.1(7)/111.2(7). The structure of a single crystal at 150 K [monoclinic, P2(1)/n, a = 4.2230(7) A, b = 11.2105(17) A, c = 12.332(2) A, beta = 94.544(16) degrees] also reveals planar molecules with the same conformation and dimensions close to those of the gaseous molecule. Changes in the vibrational spectra of the compound accompanying the transition from the vapor to the condensed phases are attributed not to the presence of more than one conformer but to differences in the local environment of the two carbonyl groups. The properties deduced are compared with those of other compounds of the type CH3C(O)XC(O)CH3 (X = CH2, NH, or O).

Trifluoroacetylsulfenyl trifluoroacetate, CF(3)C(O)-S-O-C(O)CF(3), a novel compound with a symmetrically substituted S-O bond: synthesis, spectroscopic characterization, and quantum chemical calculations.

The new compound trifluoroacetylsulfenyl trifluoroacetate, CF(3)C(O)SOC(O)CF(3), which possesses two identical carbonyl substituents attached to the S-O bond, has been synthesized. The IR and UV spectra of the gas phase as well as the (13)C NMR spectrum of the solution in CDCl(3) were recorded and assigned. Quantum chemical calculations were performed with the ab initio methods HF and MP2 and the density functional approach B3LYP. The 6-31G basis set was chosen in all calculations. The molecule possesses a skew structure, and according to all computational methods, the syn-syn structure (C=O bonds of both C(O)CF(3) groups synperiplanar to S-O bond) represents the most stable conformer. In agreement with the quantum chemical calculations, the presence of small amounts (< or =5%) of a second conformer (anti-syn) cannot be excluded on the basis of the IR spectrum. The calculated values for the torsional angle around the S-O bond (delta(C-S-O-C)) of the syn-syn form are smaller than 80 degrees (72-78 degrees). Comparison with theoretical results for the corresponding disulfide CF(3)C(O)SSC(O)CF(3) and peroxide CF(3)C(O)OOC(O)CF(3) indicates that the structural properties of sulfenyl compounds are more similar to those of disulfides than to those of peroxides.

((Fluoroformyl)imido)(trifluoromethyl)sulfur fluoride, FC(O)N = S(F)CF3: unexpected conformational properties.

The geometric structure and conformational properties of ((fluoroformyl)imido)(trifluoromethyl)sulfur fluoride, FC(O)N = S(F)CF3, are investigated by gas electron diffraction (GED) experiments, IR (gas) spectroscopy, and quantum chemical calculations (HF, MP2, and B3LYP with 6-31G* basis sets). The GED intensities are reproduced best with a mixture of 79(12)% trans-syn and 21(12)% cis-syn conformers. "Trans/cis" describes the orientation around the S=N double bond (FC(O) group relative to sulfur substituents), and "syn" refers to the orientation of the C=O bond relative to the S=N bond. From the intensities of the C=O bands in the IR (gas) spectrum, a composition of 86(8)%:14(8)% is derived. These ratios correspond to delta G0(GED) = 0.79(36) and delta G0(IR) = 1.09(35) kcal mol-1. The preference of a trans structure, around the S=N double bond is unexpected, since all imidosulfur compounds studied thus far possess a cis configuration. The conformational properties are reproduced qualitatively correctly by all theoretical calculations. The predicted energy differences delta E(HF) = 2.41, delta E(MP2) = 0.64, and delta E(B3LYP) = 0.28 kcal mol-1 are larger or slightly smaller than the experimental values. Additional theoretical calculations (B3LYP) for several imidosulfur compounds reveal that only FC(O)N=S(F)CF3, with mixed substitution at sulfur and the FC(O) group bonded to nitrogen, prefers the trans structure.

Vibrational spectra and gas phase structure of N-cyanoimidosulfurous difluoride, NCN=SF2.

The vibrational spectra, IR (gas) and Raman (liquid) of N-cyanoimidosulfurous difluoride, NCN=SF2, were recorded, and the molecular structure was determined by gas electron diffraction. The spectra were assigned by comparing the vibrational frequencies with those in related molecules and with calculated (HF, MP2, B3LYP with 6-31G(d) basis sets) values, and a normal coordinate analysis was performed. The molecule possesses a syn conformation (Ctriple bondN syn with respect to the bisector of the SF2 angle). This has been rationalized by orbital interactions of the electron lone pairs of sulfur and nitrogen with the N-C and S-F bonds, respectively, which are antiperiplanar or anticlinal to these lone pairs (anomeric effects). Quantum chemical calculations with the B3LYP and MP2 methods reproduce the experimental structure reasonably well if large basis sets (6-311G(2d,f)) are used.

Structures and conformations of trifluoromethyl fluoroformate and perfluorodimethyl carbonate.

The conformational properties and geometric structures of trifluoromethyl fluoroformate, CF(3)OC(O)F (1), and perfluorodimethyl carbonate, (CF(3)O)(2)CO (2), have been studied by matrix IR spectroscopy, gas electron diffraction (GED), and quantum chemical calculations (MP2 and B3LYP with 6-311G basis sets). In both compounds the synperiplanar orientation of the O-CF(3) groups relative to the C=O double bond is preferred. If heated Ar/1 and Ar/2 mixtures are deposited as a matrix at 14 K, new bands appear in the matrix IR spectra which are assigned to the anti form of 1 and to the syn/anti form of 2. At room temperature the contribution of the anti rotamer of 1 is 4% (DeltaH degrees = H degrees (anti) - H degrees (syn) = 1.97(5) kcal/mol), and the contribution of the syn/anti conformer of 2 is estimated to be less than 1%. These high-energy conformers are not observed in the GED experiment. The quantum chemical calculations reproduce the structural and conformational properties of both compounds satisfactorily.