Willy Gombler

SOME SELENIUM-77 AND TELLURIUM-125 NMR SPECTROSCOPIC STUDIES

Abstract Correlations between chemical shifts, the electro-nagativities of X and the ΔE value, respectively, allow the prediction of chemical shifts for CF3SeX compounds and compounds containing a C=Se moiety. Coupling constants 1 J(Se-C), 1J(Te-C), and 1J(Se-Se) of CF3Se and CF3Te compounds are considerably larger than those of corresponding CH3 compounds. The isotope effect of 13C on 77Se, 1Δ77Se(13/12C), extends over a wide range. The first correlation between isotope shifts and bond lengths was established with the aid of these data. The isotope effect of all Se isotopes in diselenides R77SenSeR (n = 74, 76, 77, 78, 80, 82), and 1Δ125Te(127.7/123Te) and 1Δ123Te(127·9/125Te) values for CF3TeTeCF3 could be measured.

A 113Cd, 19F, and 13C NMR study on perfluoroorganocadmium-diglyme adducts

Abstract 113Cd, 19F, and 13C NMR spectroscopic data of adducts of the type (Rf)2Cd·diglyme (Rf = CF3, C2F5, n-C3F7, i-C3F7, C6F6) are reported for solutions in CD3CN. The cadmium-113 shielding is interpreted in terms of Lewis acid-base complex stability; high shielding indicates high complex stability. The 113Cd, 19F, and 13C chemical shifts of the nuclei in the central moiety f C ∥ ∥ Cd are strongly dependent on the number of fluorine atoms bonded to the a-carbon because this number determines the group electro-negativity of the Rf group and the π-bond order in the FC bond. The chemical shifts correlate one with another and with the coupling constants 1J(FC)α,1J(CdC), and 2J(CdF). The coupling constants 1J(CdC) are extremely large and correlate with the group electronegativity of Rf. The large values are interpreted in terms of contraction of the carbon and cadmium orbitals by the highly electronegative substituents.

Synthesis of the unsymmetrical diselenanes CF3SeSeCF2Cl and CF3SeSeCH3

Abstract Chlorodifluoromethyl(trifluoromethyl)diselenane, CF 3 SeSeCF 2 Cl, has been prepared by the reaction of CF 3 SeCl with Se=CF 2 . CF 3 SeSeCH 3 has been synthesized via a new route from CF 3 SeSeCF 3 and CH 3 SeSeCH 3 . CF 3 SeSeCF 2 Cl is unstable with respect to the symmetric diselenanes CF 3 SeSeCF 3 and CF 2 ClSeSeCF 2 Cl. The new compound CF 3 SeSeCF 2 Cl has been characterized by 77 Se, 19 F, and 13 C NMR, IR, and mass spectra. Additional data from the 77 Se, 19 F, 13 C, and 1 H NMR spectra are reported for the known compounds CF 3 SeSeCH 3 and CF 2 ClSeSeCF 2 Cl.

Reaktionen von trifluormethylsulfenylfluorid mit olefinen und fluorolefinen

Abstract Trifluoromethylsulfenylfluoride, CF 3 SF, adds to the carbon- carbon double bond of olefins to form partially fluorinated thioethers. The reaction of CF 3 SF with CH 3 CHCH 2 gives the two isomers CH 3 CHFCH 2 SCF 3 (85–94 %) and CH 3 CH(SCF 3 )CH 2 F (6–15 %) while the addition of CF 3 SF to CF 3 CHCH 2 yields only one product, CF 3 CH(SCF 3 )CH 2 F. In contrast, CF 3 CF=CF 2 does not react with CF 3 SF at temperatures up to 20 °C. The new compounds are stable liquid materials which have been characterized by 19 F, 13 C, 1 H NMR, IR, and mass spectroscopy.

Effect of selenium isotopes on selenium-77 nuclear shielding in diselenides

The effect of all selenium isotopes on the nuclear shielding of the neighboring 77Se nucleus in CF3SeSeCF3, CH3SeSeCH3, and CF3SeSeCH3 was observed. The detection of this isotope effect helps to prove that two magnetically equivalent selenium atoms are bonded to each other in a molecule. The isotope shift per unit mass difference decreases with increasing mass of the Se isotopes. This isotope effect is sensitive toward the nature of substituents. The 77Se NMR spectrum of the CH3Se group of CF3SeSeCH3 exhibits a fine splitting for each isotopomer; this is attributed to the occurrence of two different conformers of this diselenide. Two 77Se-77Se coupling constants of 10.4 and 11.5 Hz were evaluated for the two conformers.

The unusual chemical equilibria F3SSF ⇌ 2 SF2 and CF3SF2SCF3 ⇌ 2CF3SF

Abstract In order to understand more about the instability of sulfur difluoride, we have investigated the chemical interrelations between each of the monomers SF 2 and CF 3 SF and the corresponding dimers F 3 SSF and CF 3 SF 2 SCF 3 . Thus we have found that SF 2 and CF 3 SF exist in chemical equilibria with their dimers. These equilibria are unusual because they involve two different bonds (SF and SS). The equilibrium constants and dissociation enthalpies have been determined by i.r. and mass spectroscopic measurements. The equilibrium between F 3 SSF and SF 2 is disturbed by a decomposition reaction of these compounds yielding SF 4 and SSF 2 . In both systems (1) and (2) the achievement of the equilibrium is comparatively slow at −30 to 30 °C. The rates for dissociation and decomposition are strongly surface-dependent and the kinetics of the two processes have been studied separately. Under favorable conditions the half-lives at 298 K for the dissociation of F 3 SSF and CF 3 SF 2 SCF 3 are found to be ca. 8.h and ca. 2 h, respectively, and for the decomposition of SF 2 to SF 4 and SSF 2 and CF 3 SF to CF 3 SF 3 and CF 3 SSCF 3 (p⋍13 mbar) the values are ca. 10 h and 1 year respectively.

Physikalische und spektroskopische daten von trifluormethylselenol und derivaten

Abstract The characterization of the compounds CF 3 SeX (X = H, Cl, Br, CN, CF 3 , SeCF 3 ) is completed by the report of melting points, boiling points, enthalpies of vaporization and entropies of vaporization. Ultraviolet and mass spectra are presented and discussed. An improved synthesis for CF 3 SeH is reported.

Isotope effects of 34/32S and 37/35Cl on the nuclear shielding of fluorine-19 and their correlation with bond lengths

Abstract The isotope effect of 34/32 S on the NMR frequency of 19 F has been measured for a series of sulfur fluorine compounds. The one-bond low-frequency (high-field) isotope shift 1 Δ 19 F( 34/32 S) shows a strong inverse dependence on the SF bond distance. For example, the axial F atoms of the longer SF bond in SF 4 and its derivatives give much smaller values than the equatorial ones which form a shorter SF bond. From this correlation SF bond distances of similar sulfur fluorine compounds can be predicted. The two-bond isotope shifts 2 Δ 19 F( 34/32 S) in compounds of type F 3 CS− and SC(F)X depend analogously on the CS bond distance (the CF bond length is almost constant). Together with the correlations between the isotope effects 1 Δ 77 Se( 13/12 C) [1] and 1 Δ 31 P( 15/14 N) [2], respectively, and the corresponding bond lengths, it appears that the dependence of isotope shifts on bond distances is a general phenomenon that can be applied to a series of closely related compounds. The two-bond isotope effect 2 Δ 19 F( 37/35 Cl) shows that the influence of two 37 Cl atoms on the 19 F shielding is additive and the number of Cl atoms in a group can be determined from the isotope pattern of the highly resolved spectrum.

Multinuclear NMR studies on CF3 substituted sulfur, selenium and tellurium compounds

Abstract A systematic investigation of thirty-four CF 3 Se(II, IV) and eight CF 3 Te(II, IV) compounds by 13 C, 19 F, 77 Se and 125 Te NMR spectroscopy resulted in some general features for chemical shifts and coupling constants which agree with the trends of reported 19 F and new 13 C NMR data of CF 3 S(II, IV) compounds. Moreover, the NMR spectra of molecules of the type E=CXY (E = chalcogen, X, Y = halogen) and substances containing a CSe double bond have been studied. From the comparison of these NMR data with those of CF 3 substituted chalcogen compounds, a partial double bond character of the carbon-fluorine and carbon-chalcogen bond in CF 3 substituted chalcogen compounds can be derived: