Chlorodifluoroacetyl cyanide, ClF2CC(O)CN: synthesis, structure, and spectroscopic characterization

The novel molecule difluorochloroacetyl cyanide, ClF(2)CC(O)CN, has been characterized by IR (gas phase, Ar matrix), Raman (liquid), (19)F and (13)C NMR, and photoelectron (PES) spectroscopies; photoionization mass spectrometry (PIMS); and gas electron diffraction (GED). The conformational properties of ClF(2)CC(O)CN have been studied by joint application of vibrational spectroscopy, GED, and quantum chemical calculations. The existence of two conformers is detected in the gas and liquid phases, in which the C-Cl bond adopts gauche and syn orientations with respect to the C═O group. The computed enthalpy difference is in harmony with the experimental results of the gauche being more stable than the syn conformer by ΔH° = 1.3 kcal mol(-1) (MP2/cc-pVTZ). The valence electronic properties and the possible ionization and dissociation processes of the title compound are studied using the PES and PIMS. The experimental first vertical ionization energy of 12.0 eV corresponds to the ejection of an electron of the oxygen lone pairs. Taking into account the properties and broad applications of acyl cyanides, ClF(2)CC(O)CN is a promising new precursor in preparative chemistry.     

Synthesis and characterization of sulfuryl diazide, O2S(N3)2

Sulfuryl diazide, O(2)S(N(3))(2), previously described as an "exceedingly explosive" compound, has been isolated and characterized by IR (Ar matrix, gas) and Raman (solid) spectroscopy, and its structure has been determined by X-ray crystallography. It has a melting point of -15 °C and can be handled in small quantities in gas, liquid, and solid states. Vibrational spectroscopic studies suggest the presence of only one conformer in both gas and solid states, and the X-ray crystallography revealed an anti conformation of the two azido groups with respect to the NSN plane. Calculations predict the anti (C(2)) conformer to be 6.6 kJ mol(-1) lower in energy than the syn (C(s)) one at the CBS-QB3 level of theory. The related chlorosulfuryl azide, ClSO(2)N(3), has also been prepared and characterized by IR and Raman spectroscopy.     

Vibrational and valence photoelectron spectroscopies, matrix photochemistry, and conformational studies of ClC(O)SSCl

ClC(O)SSCl was prepared by an improved method by the reaction of [(CH(3))(2)CHOC(S)](2)S with SO(2)Cl(2) in hexane. The photoelectron spectra in the gas phase present four distinct regions, corresponding to ionizations from electrons formally located at the S, O, and Cl atoms and at the C═O bond. The vibrational IR and Raman spectra of the liquid were interpreted in terms of the most stable syn-gauche conformer (the O═C double bond syn with respect to the S-S single bond and the C-S single bond gauche with respect to the S-Cl single bond) in equilibrium with the less stable anti-gauche form, both occurring in two enantiomeric forms. The randomization process between the conformers was induced by broad-band UV-visible irradiation in matrix conditions, and several photoproducts were identified by FTIR spectroscopy. The experimental results were complemented by theoretical calculations.     

Vibrational spectra, crystal structures, constitutional and rotational isomerism of FC(O)SCN and FC(O)NCS

Fluorocarbonyl thio- and isothiocyanate, FC(O)SCN and FC(O)NCS, were fully characterized by IR (gas, Ar and N(2) matrixes), Raman (liquid and solid), UV (gas), and (13)C NMR (liquid) spectroscopy, as well as single-crystal X-ray diffraction. Their vibrational and conformational properties were analyzed using matrix isolation techniques guided by quantum chemical calculation at the ab initio [MP2 and CCSD(T)], density functional theory B3LYP, and CBS-QB3 levels of theory. A complete assignment of the fundamental modes of FC(O)SCN was performed. In both the gas and liquid states, FC(O)SCN and FC(O)NCS were found to exist as two conformers (C(s) symmetry), in which the carbonyl double bond (C═O) adopts a synperiplanar (syn) and an antiperiplanar (anti) orientation with respect to either the SCN or NCS group. For FC(O)SCN, the conformational enthalpy difference, ΔH° = H°(anti) - H°(syn), was determined by matrix IR experiments to be 0.9 ± 0.2 kcal mol(-1). The conformational equilibria were evaluated by fast-cooling gaseous samples highly diluted in argon at different temperatures as cryogenic matrixes. The conformational properties of both molecules were analyzed in terms of the hyperconjugative electronic effect applying the natural bond orbital method. The kinetics of the thermal conversion of the high-energy anti into the syn FC(O)NCS conformer was studied in Ar and N(2) matrixes at cryogenic temperatures. The reversed syn → anti photoisomerization was observed using UV-vis light. Rearrangement of FC(O)SCN into FC(O)NCS was observed in the neat liquid and in solution. Under 193 nm (ArF excimer laser) irradiation, FC(O)NCS isolated in cryogenic Ar matrixes forms FC(O)SCN. At low temperature, single crystals of the two constitutional isomers were obtained using a miniature zone melting procedure. According to X-ray diffraction, they exclusively crystallize in their syn forms (C(s) symmetry) in the orthorhombic crystal system.     

Structural and conformational properties of fluoroformic acid anhydride, FC(O)OC(O)F

The conformational properties and geometric structures of fluoroformic acid anhydride, FC(O)OC(O)F, have been studied by vibrational spectroscopy, gas electron diffraction (GED), single-crystal X-ray diffraction, and quantum chemical calculations (HF, MP2, and B3LYP methods with 6-31G* and B3LYP/6-311+G* basis sets). Satellite bands in the IR matrix spectra, which increase in intensity when the matrix gas mixture is heated prior to deposition as a matrix, indicate the presence of two conformers at room temperature. According to the electron diffraction analysis, the prevailing conformer is of C(2) symmetry with both C=O bonds synperiplanar with respect to the opposite C-O bond ([sp, sp] conformer). The minor conformer [15(5)% from IR matrix and 6(11)% from GED] is predicted by quantum chemical calculations to possess an [sp, ac] structure. FC(O)OC(O)F crystallizes in the orthorhombic system in the space group P2(1)2(1)2(1) with a = 6.527(1) angstroms, b = 7.027(1) angstroms, and c = 16.191(1) angstroms and four formula units per unit cell. In the crystal, only the [sp, sp] conformer is present, and the structural parameters are very similar to those determined by GED.     

Structure and conformational properties of N-pentafluorosulfur(sulfuroxide difluoride imide) SF5N=S(O)F2: vibrational analysis, gas electron diffraction, and quantum chemical calculations

The molecular structure and conformational properties of N-pentafluorosulfur(sulfuroxide difluoride imide), SF5N=S(O)F2, have been studied by vibrational spectroscopy (IR (gas) and Raman (liquid)), by gas electron diffraction (GED), and by quantum chemical calculations (MP2 and B3LYP with (6-31G(d) and 6-311+G(2df) basis sets). According to GED, the prevailing conformer possesses a syn structure (N-SF5 bond synperiplanar with respect to the bisector of the SF2 group). Splitting of the symmetric N=S=O stretching vibration in gas and liquid spectra demonstrates the presence of a second conformer (11(5)%) with anticlinal orientation of the N-SF5 bond according to quantum chemical calculations. The geometric structure, conformational properties, and vibrational frequencies are well reproduced by quantum chemical calculations.     

Fluoroformyl trifluoroacetyl disulfide, FC(O)SSC(O)CF3: synthesis, structure in solid and gaseous states, and conformational properties

Fluoroformyl trifluoroacetyl disulfide, FC(O)SSC(O)CF3, is prepared by quantitative reaction between FC(O)SCl and CF(3)C(O)SH. The conformational properties and geometric structure of the gaseous molecule have been studied by vibrational spectroscopy (IR(gas), Raman(liquid), IR(matrix)), gas electron diffraction (GED), and quantum chemical calculations (B3LYP and MP2 methods). The disulfide bond length derived from the GED analysis amounts 2.023(3) Angstroms, and the dihedral angle around this bond, phi(CS-SC), is 77.7(21) degrees, being the smallest dihedral angle measured for noncyclic disulfides in the gas phase. The compound exhibits a conformational equilibrium at room temperature having the most stable form C(1) symmetry with a synperiplanar (sp-sp) orientation of both carbonyl groups with respect to the disulfide bond. A second form was observed in IR spectra of the Ar matrix isolated compound at cryogenic temperatures, corresponding to a conformer that possess the carbonyl bond of the FC(O) moiety in antiperiplanar position with respect to the S-S single bond (ap-sp). A DeltaH degrees = - = 1.34(11) kcal/mol has been determined by IR(matrix) spectroscopy. The structure of single crystal of FC(O)SSC(O)CF3 was determinate by X-ray diffraction analysis at low temperature using a miniature zone melting procedure. The crystalline solid (monoclinic, P2(1)/n, a = 5.240(4)Angstroms, b = 23.319(17)Angstroms, c = 6.196(4)Angstroms, beta = 113.14(3) degrees) consists exclusively of the (sp-sp) conformation. The geometrical parameters agree with those obtained for the molecule in the gas phase.     

Properties of chloroformyl peroxynitrate, ClC(O)OONO(2)

The synthesis of ClC(O)OONO(2) is accomplished by photolysis of a mixture of Cl(2), NO(2), and CO in large excess of O(2) at about -70 degrees C. The product is isolated after repeated trap-to-trap condensation. The solid compound melts at -84 degrees C, and the extrapolated boiling point is 80 degrees C. ClC(O)OONO(2) is characterized by IR, Raman, (13)C NMR, and UV spectroscopy. According to the IR matrix spectra, the compound exists at room temperature only as a single conformer. The molecular structure of ClC(O)OONO(2) is determined by gas electron diffraction. The molecule possesses a gauche structure with a dihedral angle of phi(COON) = 86.7(19) degrees , and the C=O bond is oriented syn with respect to the O-O bond. The short O-O bond (1.418(6) A) and the long N-O bond (1.511(8) A) are consistent with the facile dissociation of ClC(O)OONO(2) into the radicals ClC(O)OO and NO(2). The experimental geometry of ClC(O)OONO(2) is reproduced reasonably well by B3LYP/6-311+G(2df) calculations, whereas the MP2 approximation predicts the N-O bond considerably too long and the dihedral angle too small.     

Gas‐Phase Generation and Decomposition of a Sulfinylnitrene into the Iminyl Radical OSN

The dipolar oxathiazyne‐like sulfinylnitrene RS(O)N, a highly reactive α‐oxo nitrene, has been rarely investigated. Upon flash vacuum pyrolysis of sulfinyl azide CF₃S(O)N₃ at 350 °C, an elusive sulfinylnitrene CF₃S(O)N was generated in the gas phase in its singlet ground state and was characterized by matrix‐isolation IR spectroscopy. Further fragmentation of CF₃S(O)N at 600 °C produced CF₃ and a novel iminyl radical OSN, an SO₂ analogue, which were unambiguously identified by IR spectroscopy. Consistent with the experimental observations, DFT calculations clearly support a stepwise decomposition mechanism of CF₃S(O)N₃.     

Trifluoromethanesulfenyl acetate, CF3S-OC(O)CH3, and trifluoromethanesulfenyl trifluoroacetate, CF3S-OC(O)CF3: unexpected conformational properties

Structural and conformational properties of two sulfenyl derivatives, trifluoromethanesulfenyl acetate, CF3S-OC(O)CH3 (1), and trifluoromethanesulfenyl trifluoroacetate, CF3S-OC(O)CF3 (2), were determined by gas electron diffraction, vibrational spectroscopy, in particular with IR (matrix) spectroscopy, which includes photochemical studies, and by quantum chemical calculations. Both compounds exist in the gas phase as a mixture of two conformers, with the prevailing component possessing a gauche structure around the S-O bond. The minor form, 15(5)% in 1 and 11(5)% in 2 according to IR(matrix) spectra, possesses an unexpected trans structure around the S-O bond. The C=O bond of the acetyl group is oriented syn with respect to the S-O bond in both conformers. UV-visible broad band irradiation of 1 and 2 isolated in inert gas matrixes causes various changes to occur. Conformational randomization clearly takes place in 2 with simultaneous formation of CF3SCF3. For 1 the only reaction channel detected leads to the formation of CH3SCF3 with the consequent extrusion of CO2. Quantum chemical calculations (B3LYP/6-31G and MP2 with 6-31G and 6-311G(2df,pd) basis sets) confirm the existence of a stable trans conformer. The calculations reproduce the conformational properties for both compounds qualitatively correct with the exception of the B3LYP method for compound 2 which predicts the trans form to be prevailing, in contrast to the experiment.     

Fluorocarbonyl trifluoromethanesulfonate, FC(O)OSO2CF3: structure and conformational properties in the gaseous and condensed phases

Pure fluorocarbonyl trifluoromethanesulfonate, FC(O)OSO(2)CF(3), is prepared in about 70% yield by the ambient-temperature reaction between FC(O)SCl and AgCF(3)SO(3). The geometric structure and conformational properties of the gaseous molecule have been studied by gas electron diffraction (GED), vibrational spectroscopy [IR(gas), IR(matrix), and Raman(liquid)] and quantum chemical calculations (HF, MP2, and B3LYP with 6-311G basis sets); in addition, the solid-state structure has been determined by X-ray crystallography. FC(O)OSO(2)CF(3) exists in the gas phase as a mixture of trans [FC(O) group trans with respect to the CF(3) group] and gauche conformers with the trans form prevailing [67(8)% from GED and 59(5)% from IR(matrix) measurements]. In both conformers the C=O bond of the FC(O) group is oriented synperiplanar with respect to the S-O single bond. The experimental free energy difference between the two forms, DeltaG degrees = 0.49(13) kcal mol(-1) (GED) and 0.22(12) kcal mol(-1) (IR), is slightly smaller than the calculated value (0.74-0.94 kcal mol(-1)). The crystalline solid at 150 K [monoclinic, P2(1)/c, a = 10.983(1) A, b = 6.4613(6) A, c = 8.8508(8) A, beta = 104.786(2) degrees ] consists exclusively of the trans conformer.     

Matrix isolation IR spectroscopic and ab initio studies of C(3)N(-) and related species

Coupled cluster calculations were carried out for C(3)N(-), CCNC(-), C(3)N, CCNC, C(3)N(+), and C(3)O. They support the experimental identification of the C(3)N(-) ion by means of matrix isolation infrared (IR) spectroscopy. The anion was generated in electric discharges through the cyanoacetylene isotopomers HC(3) (14)N, HC(3) (15)N, and (2)HC(3)N, trapped in cryogenic rare gas matrices (Ne, Ar, Kr), and detected via its two most intense IR absorption bands, assigned to the nu(1) and nu(2) stretching vibrations. C(3)N(-) appears to be quite a stable anion, with a vertical detachment energy predicted to be as high as 4.42 eV. A large equilibrium electric dipole moment of 3.10 D facilitates the investigation of C(3)N(-) by microwave spectroscopy and radio astronomy. Various structural parameters and spectroscopic properties have been calculated for all tetra-atomic species considered.     

Thermal decomposition mechanisms of the methoxyphenols: formation of phenol, cyclopentadienone, vinylacetylene, and acetylene

The pyrolyses of the guaiacols or methoxyphenols (o-, m-, and p-HOC(6)H(4)OCH(3)) have been studied using a heated SiC microtubular (μ-tubular) reactor. The decomposition products are detected by both photoionization time-of-flight mass spectroscopy (PIMS) and matrix isolation infrared spectroscopy (IR). Gas exiting the heated SiC μ-tubular reactor is subject to a free expansion after a residence time of approximately 50-100 μs. The PIMS reveals that, for all three guaiacols, the initial decomposition step is loss of methyl radical: HOC(6)H(4)OCH(3) → HOC(6)H(4)O + CH(3). Decarbonylation of the HOC(6)H(4)O radical produces the hydroxycyclopentadienyl radical, C(5)H(4)OH. As the temperature of the μ-tubular reactor is raised to 1275 K, the C(5)H(4)OH radical loses a H atom to produce cyclopentadienone, C(5)H(4)═O. Loss of CO from cyclopentadienone leads to the final products, acetylene and vinylacetylene: C(5)H(4)═O → [CO + 2 HC≡CH] or [CO + HC≡C-CH═CH(2)]. The formation of C(5)H(4)═O, HCCH, and CH(2)CHCCH is confirmed with IR spectroscopy. In separate studies of the (1 + 1) resonance-enhanced multiphoton ionization (REMPI) spectra, we observe the presence of C(6)H(5)OH in the molecular beam: C(6)H(5)OH + λ(275.1?nm) → [C(6)H(5)OH ?] + λ(275.1nm) → C(6)H(5)OH(+). From the REMPI and PIMS signals and previous work on methoxybenzene, we suggest that phenol results from a radical/radical reaction: CH(3) + C(5)H(4)OH → [CH(3)-C(5)H(4)OH]* → C(6)H(5)OH + 2H.     

S-(fluoroformyl)O-(trifluoroacetyl) thioperoxide, FC(O)S-OC(O)CF3: gas-phase structure and conformational properties

The geometric structure and conformational properties of S-(fluoroformyl)O-(trifluoroacetyl) thioperoxide, FC(O)S-OC(O)CF3, were investigated by gas electron diffraction, matrix isolation infrared spectroscopy, and quantum chemical calculations (B3LYP with the 6-31G and aug-cc-pVTZ basis sets and MP2 with the 6-31G basis set). The experimental methods result in a mixture of two conformers with gauche conformation around the S-O bond. In the main conformer (82(7)% according to GED at 298 K), the C=O bond of the FC(O) group is oriented syn with respect to the S-O bond and phi(C-S-O-C) = 75(3) degrees . In the minor conformer (18(7)%), this C=O is oriented anti. Both conformers possess syn orientation of the C=O bond of the CF3C(O) group. The conformational properties and geometric parameters are reproduced reasonably well by the quantum chemical calculations, except for the S-O bond length, which is predicted too long by 0.04 A (B3LYP/aug-cc-pVTZ).     

Preparation and properties of trifluorothioacetic acid-S-(trifluoromethyl)ester, CF3C(O)SCF3

Trifluorothioacetic acid-S-(trifluoromethyl)ester, CF3C(O)SCF3, was prepared by reacting CF3C(O)Cl and AgSCF3 at 50 degrees C. The compound was characterized by (13)C-, (19)F-NMR, UV, and vibrational spectroscopy as well as by gas electron diffraction (GED) and quantum chemical calculations (HF, MP2, and B3LYP methods 6-31G(d) and 6-311+G(2df) basis sets). GED and vibrational spectroscopy result in the presence of a single conformer with C1 symmetry and synperiplanar orientation of the S-CF3 bond relative to the CO bond. This result is in agreement with quantum chemical calculations which predict the anti conformer to be higher in energy by about 4 kcal/mol. An assignment of the IR (gas) and Raman (liquid) spectra is proposed, and the GED analysis results in the following skeletal geometric parameters (r(a) and angle(a) values with 3sigma uncertainties; these parameters are thermal averages and are not inconsistent with calculated equilibrium values): C=O = 1.202(6) A, C-C = 1.525(10) A, S-C(sp(2)) = 1.774(3) A, S-C(sp(3)) = 1.824 (3) A. O=C-C = 118.7(21) degrees, O=C-S = 127.1(15) degrees, C-S-C = 99.8 (13) degrees.     

Structure and conformations of N-(fluoroformyl)imidosulfurous dichloride,FC(O)N=SCl2

The IR (gas) and Raman (liquid) spectra of FC(O)NSCl(2) demonstrate the presence of a conformational mixture in both phases. According to a gas electron diffraction study, the main conformer (94(8)%) possesses a syn-syn structure (C(O)F group synperiplanar with respect to the SCl(2) bisector and the C=O bond synperiplanar to the N=S bond). Quantum chemical calculations (HF, B3LYP and MP2 with 6-31G basis set, and MP2/6-311(2df)) predict a syn-anti structure for the second conformer. Analysis of the IR (gas) spectrum results in a contribution of 5(1)% of the minor form, corresponding to a Gibbs free energy difference DeltaG degrees = G degrees (syn-anti) - G degrees (syn-syn) = 1.75(15) kcal/mol. This value is reproduced very well by quantum chemical calculations, which include electron correlation effects (DeltaG degrees = 1.28-1.56 kcal/mol). The HF approximation overestimates this energy difference (DeltaG degrees = 3.24 kcal/mol).     

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.     

Matrix photochemistry of syn-(chlorocarbonyl)sulfenyl bromide, syn-ClC(O)SBr: precursor to the novel species anti-ClC(O)SBr, syn-BrC(O)SCl, and BrSCl

The vapor of (chlorocarbonyl)sulfenyl bromide, ClC(O)SBr, was isolated in solid Ar, Kr, N(2), and Ar doped with 5% CO at 15 K, and the matrix was subsequently irradiated with broad-band UV--visible light (200 < or = lambda < or = 800 nm), the changes being followed by reference to the IR spectrum of the matrix. The initial spectrum showed the vapor of ClC(O)SBr to consist of more than 99% of the syn form (with the C==O bond syn with respect to the S--Br bond) in equilibrium with less than 1% of the anti conformer. Irradiation caused various changes to occur. First, conformational randomization took place, leading to a roughly equimolar mixture of the two rotamers, and so affording the first spectroscopic characterization of an anti-ClC(O)S-containing compound. Simultaneously, the novel constitutional isomer syn-BrC(O)SCl was also formed. Continued photolysis resulted in the decay of all these species while revealing a third reaction channel, leading to the elimination of CO and the formation of the new triatomic sulfur halide BrSCl. The assignment of the IR bands to the different products was made on the basis of the usual criteria, taking account (i) of the effects of the naturally occurring isotopic pairs (35)Cl/(37)Cl and (79)Br/(81)Br, (ii) of the vibrational properties of related molecules, and (iii) of the properties predicted for the relevant molecules by quantum chemical calculations.     

Trifluoroselenoacetic acid, CF(3)C(O)SeH: preparation and properties

The hitherto unknown trifluoroselenoacetic acid was prepared through the reaction of trifluoroacetic acid with Woollins' reagent. The compound was fully characterized by mass spectrometry, (1)H, (19)F, (77)Se, and (13)C NMR, UV-visible, IR and Raman spectroscopy, and the boiling point at 46 °C was estimated from the vapor pressure curve. An IR matrix isolation study revealed the presence of two different syn-anti and anti-syn conformers. The IR spectra of the two stereoisomers have been assigned, aided by DFT, and ab initio calculations. The UV photolysis of Ar matrix isolated CF(3)C(O)SeH yielded CO, OCSe, CF(3)SeH, and CHF(3). Apart from CF(3)SeH, these products were also obtained by vacuum flash-pyrolysis (310 °C) of gaseous CF(3)C(O)SeH. Instead of CF(3)SeH, CF(2)Se, and HF were detected among the pyrolysis products. The different decomposition pathways of CF(3)C(O)SeH are discussed.