Synthese et proprietes chimiques de deux diazoalcanes α-thiophosphores. observation d'un couplage 4jpp

Transfer of diazo and/or azide groups to the methylene of phosphine sulfides 1 Ph₂P(S) CH₂R, leads to the diazoalkanes Ph₂P(S)CN₂R 2b and 2c and azides Ph₂P(S)CHN₃R 3a and 3c in good yields. Thermolysis and photolysis in various media are studied. The 1,3-dipolar addition of 2c on trans dibenzoyléthylène and ethylfumarate is followed by Ph₂P(S) group migration. The corresponding carbenes give very complex reactions causing P-C bond breaking. New coupling constants ⁴J_PP and J_PC are observed.     

29Si-NMR-spektroskopische untersuchungen an substituierten disilanen

The ²⁹Si chemical shifts δ(Si) and coupling constants J(SiSi) and J(SiC) for a series of substituted tetra- and penta-methyldisilanes are reported and discussed as well as the corresponding data of di- and poly-silanes from the literature. The substituent effects of /gd(Si) can be explained satisfactorily by a simple quantum-chemical model without consideration of d-orbital effects and are mainly affected by the distribution of the /gs-electron density at the Si atom under study. The influence of steric interactions on δ(Si) is investigated in the case of alkoxy-substituted disilanes. A short discussion of the substituent effects on the coupling constants J(SiSi) and J(SiC) is given.     

NMR study (1H, 13C and 29Si) of (CH3)4−x Si(CHCH2)x compounds where x = 0, 1, 2, 3, 4

The ¹H, ¹³C and ²⁹Si NMR spectra of the various methylvinylsilanes have been analysed with the aid of a special simulation program. From considerations of the chemical shifts and of the coupling constants ^2,3j_¹H-¹H, ¹J_¹³C-¹H, ¹J_{²⁹Si-¹³C} and ²J_{²⁹Si-C-¹H} it is shown that a mesomeric —M effect from the vinyl group to the Me—Si group is important, in very good agreement with previously published PES results [1–3]. The mesomeric interaction in this series is ascribed to a {d, σ^*—π} hyperconjugation in accordance with theoretical considerations [4].     

Trends in 19F-19F and 29Si-19F coupling constants in organosilicon derivatives containing SiF2 and Si2F4 units

Consideration of ¹⁹F-¹⁹F and ²⁹Si-¹⁹F coupling constants in a series of organosilicon derivatives containing SiF₂ and Si₂F₄ units reveals a number of trends which are useful for structural and stereochemical assignments. For example the vicinal ¹⁹F-¹⁹F coupling constants in a number of CSiF₂SiF₂C- derivatives (including straight chain compounds, disilacyclobutanes and disilacyclohexanes) show an apparent linear dependence on dihedral angle, varying in magnitude from near zero for small values of φ up to ca. 19 Hz for φ ～ 180°. This is particularly useful for stereochemical assignments [1,2]. In addition ²⁹Si-¹⁹F coupling constants appear to fall in quite distinct ranges (¹J_SiF > 300 Hz, 29 Hz < ²J_SiF < 55 Hz, ³J_SiF < 10 Hz). This is quite useful for structural assignments [1,6]. Reaction of SiF₂ with 1,3-cyclohexadiene gives two new silicon fluorine compounds: a disilabicyclo[2,2,2]octene and an HSi₂F₅-substituted cyclohexadiene.     

29Si and 13C NMR spectra of permethylpolysilanes

²⁹Si, ¹³C and ¹H NMR spectra are reported for the series of linear permethylpolysilanes Me(SiMe₂)_nMe where n = 1 to 6, for the cyclic permethylpolysilanes (Me₂Si)_n where n = 5 to 8, and for a few related compounds. For linear polysilanes the ²⁹Si and ¹³C chemical shifts can be accurately calculated from simple additivity relationships based on the number of silicon atoms in α, β, γ and δ positions. Adjacent (α) silicon atoms lead to upfield shifts in the ²⁹Si and ¹³C resonances, whereas more remote silicon atoms lead to downfield shifts. The ²⁹Si chemical shifts of the polysilane chains are linearly related to the ¹³C shifts of the carbon atoms attached to the silicon. The ²⁹Si and ¹³C resonances of the cyclic silanes deviate from this relationship. Ring current effects arising from σ delocalization are suggested as an explanation for the deviations. Proton-coupled ²⁹Si NMR spectra are reported for Me₃SiSiMe₃ and for (Me₂Si)_n, n = 5 to 7.     

Calculation of the 1J(PP) angular dependence in P2H4

Using the results obtained from an MO SCF ab initio calculation on P₂H₄ in four different conformations, the ¹J(PP) NMR coupling constants have been calculated. The ¹J(PP) values are highly dependent upon the rotational angle φ (?238.0 Hz in the eclipsed conformation, 10.9 Hz in the staggered one). The shape of the theoretical ¹J(PP) plot seems to be in good agreement with experimentally measured ¹J(PP) values.     

D-nuclear quadrupole coupling in the rotational spectrum of 15N2…DF and an interpretation of the hyperfine coupling constants χ aaD and DaaHF within a series of complexes B…HF

Hyperfine structure in the J = 1 ← 0 and J = 2 ← 1 transitions of ¹⁵N₂…DF, arising from D-nuclear quadrupole coupling and D, ¹⁹F nuclear-spin—nuclear-spin coupling, has been observed and measured by using pulsed-nozzle Fourier-transform microwave spectroscopy. The following rotational, centrifugal distortion and hyperfine coupling constants were determined: β_o = 3091.9004 MHz, D_J = 14.75 kHz, χ_aa^D = 278.6(38) kHz and D_aa^HF = ?38.5(38) kHz. An interpretation is presented for the variation of the coupling, constants χ_aa^D and D_aa^HF along the series B…DF and B…HF, where B = Ar, Kr, Xe, ¹⁵N₂, CO, PH₃, H₂S, HC¹⁵N and H₂O.     

Über die Stärke der Si—Si-bindung in Abhängigkeit vom Substituenten

The strength of the Si?Si-bond in disilanes varies with the substituents of silicon. It is shown, that the increase of the Si?Si stretching force constant inX ₃SiSiX ₃ parallels an increase of the SiH-stretching force constant in the correspondingX ₃SiH-compound. The coupling constantJ(²⁹SiH) alters in a similar manner. Exceptions are found in same disilanes with strong d π p π-interactions from the substituents.     

Reaction rate studies of atomic germanium (3P0,1) and silicon (3PJ) with various oxidizers

The gas phase reactions of Ge(³P_0,1) and Si(³P_J) with O₂, NO and N₂O have been studied in a flow tube system at 350 K. Atomic Ge and Si were produced by flowing GeH₄ and SiH₄ through a hollow cathode discharge. The subsequent disappearance of the Ge and Si atoms was followed with atomic absorption spectroscopy. Rate constants were determined for the reactions at 4 and 5 torr pressures.     

Calculation of 1J(13C-29si) spin-spin coupling constants by the maximum overlap approximation method

The spin-spin ¹J(C-Si) coupling constants were calculated by the maximum overlap approximation method for a series of related organosilicon compounds. It was concluded that the variation in hybridization of the relevant carbon atom accounts for the changes in ¹J(C-Si) observed experimentally.     

Fourier transform NMR investigations of 13C labeled silyl and stannyl acetylenes

The ¹³C NMR spectra of ¹³C labeled mono- and di-substituted silyl- and stannyl-acetylenes have been studied. It was found that the values of ¹J(CC) coupling constants between acetylenic carbons decrease very sharply in the series Alk₃SiCCH, Alk₃SnCCH, Alk₃SiCCSiAlk₃ and Alk₃SnCCSnAlk₃. These results and the observed changes in the geminal hetero-atom β-acetylenic carbon couplings suggest a very strong p_πd_π interaction between the π-electrons of the triple bond and the vacant d orbitals of silicon and tin.     

Etude par RMN 13C Et 199Hg de composes oxobromo- et dioxomercuriques

Organomercuric compounds of the general formula

and [RCOCH(R′)]₂Hg, obtained from three ketones, 2,2-dimethyl 3-pentanone, 1-mesityl 1-propanone and 1-mesityl 1-ethanone, have been studied by ¹³C and ¹⁹⁹Hg NMR techniques. Coupling constants J(CHg) and J(HgH) are consistent with C-metalated species; in each case the values of δ(C(2)) and J(C(2)H) observed are higher than expected for purely sp³ carbon. The contribution of O-metalated species and hyperconjugative effects are discussed. For two dioxomercuric compounds (R′  Me, R  t-Bu, mesityl) the existence of diastereoisomers is suggested from ¹⁹⁹Hg NMR data.     

Rotational isomerism. A gas-phase 1H nuclear magnetic resonance study of 1-bromo-2-chloroethane

The average vicinal coupling constants of 1-bromo-2-chloroethane at different temperatures have been obtained in a gas-phase ¹H NMR study of 1,2-disubstituted ethanes. Analysis of the experimental data, assuming a ”static” model with constant values for the vicinal coupling constants of the individual rotamers, yielded unacceptable results. A ”dynamic” model, which takes into account the torsional vibrations, has therefore been developed and used to analyse the gas-phase results. The values at 305 K for the vicinal coupling constants of the individual rotamers are: trans rotamer J_T = 13.6 Hz, J'_t = 4.9 Hz; gauche rotamer $\text{1}\text{2}$(J_G1 + J_G2) = 0.9 Hz, $\text{1}\text{2}$(J'_G1 + J'_G2) = 7.8 Hz. These couplings are temperature-dependent with J_T changing about four times as much as the other coupling constants. Analysis of the average vicinal coupling constants, measured in different solvents, with the “dynamic” model gave values for the vicinal coupling constants of the individual rotamers in excellent agreement with those from the gas-phase data. The value of $\text{1}\text{2}$(J_G1+ J_G2) decreases noticeably with increasing dielectric constant of the solution. This can be explained by changes in the average dihedral angle between the coupling protons, in the gauche rotamers, which leads to changes of J_G1 and J_G2 in the same direction.     

NMR study (1H, 13C and 29Si) of the methylallylsilanes

¹H, ¹³C and ²⁹Si NMR data for the compounds (CH₃)_xSi(CH₂CHCH₂)_4-x are reported. The ¹H resonances from the π system are indicative of the electron-supplying inductive effect (+I) of the (CH₃SiCH₂, moiety but the corresponding ¹³C_π chemical shifts seem to be influenced by a sterically induced polarization of the C-H bonds. The ¹³C_All, ¹³C_Me and ²⁹Si chemical shift data reveal an important neighbour anisotropy contribution originating from the π system. Ultraviolet study of the compounds mentioned above gives indication of a σ—π conjugation in accordance with PES and ab initio results [1—5]. The trend observed in the various coupling constants is too small to be Interpreted.     

Kinetic study of electronically excited silicon atoms,Si(3p2(1S0)), by time-resolved attenuation of atomic resonance radiation

The collisional behaviour of electronically excited silicon atoms in the 3p²(¹S₀) state, 1.909 eV above the 3p²(³P₀) ground state, is investigated by time-resolved attenuation of atomic resonance radiation at λ = 390.53 nm (4s(¹P^o₁)←3p² (¹S₀)). The optically metastable Si(3¹S₀) atoms were generated by the repetitive pulsed irradiation of SiCl₄ and their decay monitored in the presence of added gases. Absolute quenching rate constants (k_Q, cm³ molecule^?1 s^?1, 300 K) are reported for the following collision partners: He (?1.3 × 10^?15), SiCl₄ ((9.1 ± 1.4) × 10^?11), O₂ ((1.5 ± 0.2) × 10^?11) and N₂O ((4.3 ± 0.4) × 10^?11). The results for O₂ and N₂O are compared with analogous data reported hitherto for Si(3p²(³P_J)) and with those for the other np²(¹S₀) states of the group IV atoms C, Ge, Sn and Pb. The rate data for the silicon atoms are considered in terms of the nature of the potential surfaces arising from symmetry arguments based on the weak spin orbit coupling approximation.     

Die metall-kohlenstoff-bindung in carben- und carbin-komplexen. aussagen der 183W13C-kopplungen

The nuclear spin coupling constants¹J(¹⁸³W¹³C) and in some cases ²J(¹⁸³W¹³C) and ³J(¹⁸³W¹³C) are determined for 10 tungsten carbene and 9 tungsten carbyne complexes. ¹J is of analytical importance, being characteristically greater for WC than for WC bonds. This is due to different hybridisation at the carbon atom, and provides information about bond angles and polarities of WC and WCR units.Substituents R and R' in (CO)₅WCRR' and X(CO)₄WCR as well as the halogens X lead to minor changes in ¹J. These changes are comparable to those of ¹J(¹³C¹H) in correspondingly substituted methanes. Unexpectedly ¹J in_ creases with X = Cl, Br, I. ²J(¹⁸³W¹³C) though being much smaller than ¹J reflects different hydridisation at the β carbon atom.     

1H,13C and 199Hg NMR study on the spin-spin coupling constants and Rα-structure of CF3HgCH3 in isotropic and nematic phases

The C-H, C-F, Hg-C, Hg-H and Hg-F spin-spin coupling constants of CF₃HgCH₃ in hexadeuterobenzene have been determined. The last two of these coupling constants have been also measured in nematic Merck ZLI 1167, ZLI 1132 and Phase IV liquid crystals heated to isotropic states. It appears that these coupling constants are solvent and temperature dependent; J(Hg-F), m particular, varies from 942.7 Hz to 955.1 Hz in nematic solvents and has a value of 926.4 Hz in a benzene solution.The distance ratios obtained in the aforesaid nematic solvents by using direct dipole-dipole coupling constants corrected for harmonie vibrations agree within the error limits. However, serious trouble arises in determining the positions of the fluorine nuclei. These difficulties arise partly from the low relative precisions of the dipole-dipole coupling constants and partly from the indirect contributions in the experimental values.     

13C, 15N and 29Si nuclear magnetic resonance studies of some aminosilanes and aminodisilanes

¹³C, ¹⁵N (at natural abundance) and ²⁹Si NMR data (chemical shifts and coupling constants) are reported for aminosilanes R₂R′SiNHR¹ (1), bis(silyl)amines Me₂R′SiNHSiMe₃ (2), 1,2-bis(amino)-ethanes (3), bis(amino)silanes RR′Si(NHR¹)₂ (4), 1,2-bis(amino)tetramethyldisilanes (5) and 1,1,2,2-tetrakis(amino)dimethyldisilanes (6). The δ¹⁵N values depend more on the nature of the substituents R¹(H, alkyl, aryl) at the nitrogen atom (in the same way as for other amines) than on different substituents at the silicon atom. A linear correlation between ¹J(²⁹Si¹⁵N) and ¹J(²⁹Si¹³C) is proposed for silanes in which the SiN unit is replaced by the SiCH unit. This correlation comprises all ¹J(²⁹Si¹⁵N) values for aminosilanes R_4-nSi(N)n (n = 1–4) and—most likely—also for aminodisilanes, and it predicts ¹J(²⁹Si¹⁵N)>0 if the corresponding value |¹J(²⁹Si¹³C)|>25 Hz. For the first time a two-bond coupling across Si, ²J(²⁹Si ¹⁵N) = 6.9 Hz, has been observed for 6a. In the case of 6b (R¹ = ^sBu) all resonances for the diastereomers are resolved in the ¹⁵N and ²⁹Si NMR spectra in contrast to the ¹H and ¹³C NMR spectra.     

The preparation and 119Sn and 19F NMR spectra of some trifluoromethylphenyltin(IV) compounds

The preparation of a series of new trifluoromethylphenyltin(IV) compounds, Bu_nSn(C₆H₄CF₃-3)_4-n, (C₆H₄CF₃-3)SnCl₃, (C₆H₄CF₃-2)SnCl₃, and some related adducts with 2,2¹-bipyridyl and 1,10-phenanthroline, is described. ¹¹⁹Sn and ¹⁹F chemical shifts have been determined, together with values of J(¹¹⁹Sn=F) and ³J(¹¹⁹Sn=H_itortho), and the possibility of a “through space” tinfluorine coupling mechanism is also discussed.     

Inductive substituent constants σji from olefinic geminal 1h, 1h nmr coupling constants

Theoretical and experimental arguments are presented supporting the postulate that olefinic NMR coupling constants ²J_HH are insensitive to β-substituent influences on the olefinic π orbital. A new set of substituent constants, σ^J_I, is proposed to measure directly the inductive substituent effect transmitted by σ-bonds. The previously available range of inductive substituent constants can be appreciably extended in this way. Comparisons of σ^J_I with other observables and parameters for selected substituents are made as a test of consistency.