Matrix infrared spectra (4000–400cm−1) have been recorded for (fluorocarbonyl)sulfenyl isocyanate, FC(O)SNCO, (fluorocarbonyl)trifluoromethylsulfane, FC(O)SCF3 and (chlorocarbonyl)trifluoromethylsulfane, ClC(O)SCF3. Subsequent variable temperature and photochemical studies have been carried out. Both syn and anti forms have been identified in the gas phase for FC(O)SCF3, but the syn conformer is thermodynamically more stable than the anti rotamer. A randomization process is clearly observed when the compound isolated in Ar at cryogenic temperatures is irradiated with broad band UV–visible light. Both FC(O)SNCO and ClC(O)SCF3 molecules show a single syn conformation. Moreover, for FC(O)SNCO matrix variable temperature deposition experiments and exposure of the matrix to broad band UV–visible light do not imply in changes revealing conformational equilibrium in the gas phase. For ClC(O)SCF3 a photochemical test does not originate any interconversion. Although the decomposition of FC(O)SCF3 and ClC(O)SCF3 originates beside CO known compound (CF3SF and CF3SCl), the FC(O)SNCO could be used to isolate the hitherto unknown FSNCO species. For this molecule several theoretical calculations have been carried out to forecast its properties and structure.

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.

The tautomeric equilibria of the β-ketoesters [CH3C(O)CH2C(O)OCH3 (I), CH3C(O)CHClC(O)OCH3 (II), CH3C(O)CH2C(O)OCH2CH3 (III) and CH3C(O)CHClC(O)OCH2CH3 (IV)] were studied by NMR spectroscopy and, in the case of I and II, by quantum chemical calculations (ab initio and density functional methods). In addition, liquid-state Fourier transform infrared and Raman spectra were analysed for all four compounds. They revealed the existence of two tautomers, diketo and enol forms. In the NMR spectra only signals for the diketo form could be observed for I and III. However, the calculations for I and II predicted the enol structures to be the most stable species. Copyright © 2001 John Wiley & Sons, Ltd.

The disulfides FC(O)SSCF3, ClC(O)SSCF3 and ClC(O)SSCH3 have been prepared by new synthetic routes. Infrared and Raman spectra have been recorded and assigned. From the vibrational spectra and from the gas electron diffraction experiment it was concluded that FC(O)SSCF3 exists as a mixture of syn- and anti-conformers (CO synperiplanar/antiperiplanar to SS bond). The main conformer (83(5)% and ΔG°=G°(anti)−G°(syn)=0.95(28)kcalmol−1) possesses syn-structure. The vibrational spectra of the chlorocarbonyl disulfanes are interpreted in terms of a single conformer, but small amounts (<5%) of a second conformer cannot be excluded. Quantum chemical calculations (HF, MP2, B3PW91 with 6-31G∗ basis sets) reproduce the experimental results (conformational properties, geometric structure and vibrational frequencies) satisfactorily. The predicted difference in Gibbs free energy, ΔG°, for FC(O)SSCF3 varies between 0.8 and 1.5kcalmol−1, those for the chlorine derivatives are larger than 2.6kcalmol−1.

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.

The molecular structures and conformational properties of acetyl peroxynitrate (PAN, CH3C(O)OONO2) and trifluoroacetyl peroxynitrate (FPAN, CF3C(O)OONO2) were investigated in the gas phase by electron diffraction (GED), microwave spectroscopy (MW), and quantum chemical methods (HF/3-21G, HF/6-31G*, MP2/6-31G*, B3PW91/6-31G*, and B3PW91/6-311+G*). All experimental and theoretical methods show the syn conformer (C=O bond of acetyl group syn to O-O bond) to be strongly predominant relative to the anti conformer. The O-NO2 bonds are extremely long, 1.492(7) A in PAN and 1.526(10) A in FPAN, which correlates with their low bond energy and the easy formation of CX3C(O)OO* and *NO2 radicals in the atmosphere. The O-O bonds (1.418(12) A in PAN and 1.408(8) A in FPAN) are shorter than that in hydrogen peroxide (1.464 A). In both compounds the C-O-O-N dihedral angle is close to 85 degrees.

Pure, highly explosive CF(3)C(O)OOC(O)CF(3) is prepared for the first time by low-temperature reaction between CF(3)C(O)Cl and Na(2)O(2). At room temperature CF(3)C(O)OOC(O)CF(3) is stable for days in the liquid or gaseous state. The melting point is -37.5 degrees C, and the boiling point is extrapolated to 44 degrees C from the vapor pressure curve log p = -1875/T + 8.92 (p/mbar, T/K). Above room temperature the first-order unimolecular decay into C(2)F(6) + CO(2) occurs with an activation energy of 129 kJ mol(-1). CF(3)C(O)OOC(O)CF(3) is a clean source for CF(3) radicals as demonstrated by matrix-isolation experiments. The pure compound is characterized by NMR, vibrational, and UV spectroscopy. The geometric structure is determined by gas electron diffraction and quantum chemical calculations (HF, B3PW91, B3LYP, and MP2 with 6-31G basis sets). The molecule possesses syn-syn conformation (both C=O bonds synperiplanar to the O-O bond) with O-O = 1.426(10) A and dihedral angle phi(C-O-O-C) = 86.5(32) degrees. The density functional calculations reproduce the experimental structure very well.

The geometric structure and conformational properties of the two inhalation anesthetics desflurane (2-difluoromethoxy-1,1,1,2-tetrafluoroethane, CF3–CHF–O–CHF2) and isoflurane (2-chloro-2-(difluoromethoxy)-1,1,1-trifluoroethane, CF3–CHCl–O–CHF2) were studied by gas electron diffraction (GED) and quantumchemical calculations (HF/3-21G*, B3PW91/6-311G(2d) and MP2/6-311G(2d)). Both compounds exist in the gas phase as mixtures of two conformers. The predominant form (80(8)% in desflurane and 83(11)% in isoflurane) possesses near trans configuration of the C–C–O–C skeleton (φ(C–C–O–C)=−146(4)° in desflurane and −136(5)° in isoflurane) and trans orientation of the CHF2 group (C–H bond trans to O–C bond). In the minor conformer, the CHF2 group is oriented gauche. These conformational properties are discussed in terms of anomeric effects. According to the theoretical calculations four or five stable conformers exist and the types and relative energies depend on the computational method. However, the two structures which are predicted by all three methods to be lowest in energy correspond to the predominant and minor conformer observed in the GED experiments. The gas phase structures of the predominant form are in very close agreement with the crystal structures which have been reported previously.

IR and Raman spectra were recorded for liquid trichloromethanesulphenyl cyanide, CCl3SCN, Quantum chemical calculations were carried out on the molecules CX3SCN (X = Cl, F, H) with ab intio (HF, MP2) and density functional methods (BPW91, B3PW91), According to all computational approaches the compounds CX3SCN posses C-s symmetry and a staggered orientation of the CX3 group with respect to the S-C=N group, On the basis of these results, a wavenumber assignment is proposed in terms of C-s symmetry. Copyright (C) 2000 John Whey & Sons, Ltd.

The molecular structure and conformational properties of perfluorodimethyl trithiocarbonate, (CF3S)2CS, were studied by gas electron diffraction (GED), vibrational spectroscopy and quantum chemical calculations (HF, MP2 and B3PW91 with 6-31G∗ basis sets). From Raman spectra a composition of 60(10)% (syn,syn) and 40(10)% (syn,anti) conformers (ΔG0=0.2(2)kcalmol−1) was derived for the liquid state. Syn/anti describes the orientation of the S–CF3 bonds relative to the CS bond. The GED investigation resulted in a mixture of 84(12)% (syn,syn) and 16(12)% (syn,anti) conformers for the gas phase (ΔG0=1.0(5)kcalmol−1). The calculations predict energy differences between the two conformers from 0.4 (B3PW91) to 0.9 (HF)kcalmol−1. The predominant (syn,syn) form possesses a non-planar sulfur–carbon skeleton of C2 symmetry with the S–CF3 bonds rotated out of the CS3 plane (φ(SC–S–C)=32(4)°). The theoretical calculations predict a planar or nearly planar skeleton for the (syn,anti) conformer. All three computational methods reproduce bond lengths and bond angles very well.

Quadrupolar and dipolar relaxation times have been determined for pyrrole, 3,4-bis(trifluoromethyl)-pyrrole and their H-bonded complexes with pyridine. Correlation times, activation energies and quadrupole coupling constants are compared. Correlation times of imido-, α- and β-protons of pyrrole are used as probes for a qualitative discussion of the anisotropic reorientation of pyrrole and the pyrrole—pyridine complex.