Electron diffraction studies of the molecular structures of iron(II) chloride and iron(II) bromide. Evidence on the structure of dimeric species Fe2Br4

An expression for the extreme values of mean-square amplitudes of vibrations in polyatomic molecules has been derived which permits estimation of the mean-square amplitude without solving the vibrational problem. This expression can be improved for the stretching and scissoring modes when the assignment of frequencies is known. In turn, the corresponding vibrational frequency may be estimated from the experimental value of the mean-square amplitude. The mean-square amplitudes of the butadiene-1,3 molecule are considered as an example.     

Réactions des céténes et du dicéténe avec les germyl- et silylphosphines

Ketenes add to germyl- and silylphosphines R₃MPEt₂ with opening of the carbonyl group and formation of phosphorylated alkenoxygermanes or -silanes

(R′H, Ph). These adducts are thermally stable and only the addition derivative of diphenylketene and Me₃SiPEt₂ exhibits metallotropic isomerization to a C-derivative after prolonged heating. Hydrolysis of these addition compounds is a new approach to the acylphosphines R₂CH-CO-PEt₂. Diketene also reacts with germyl- and silylphosphines with acyloxygen bond cleavage and formation of metallated and phosphorylated ketoenolates of the type

. These derivatives isomerize either partially (MSi) or completely (MGe) into R₃MOC(CH₃)CHCOPEt₂. Their hydrolysis constitutes a new method of synthesis of the phosphorylated β-diketone

. The ketoenolates from the addition reaction of the hydrosilylphosphine, Me₂Si(H)PEt₂, cyclize readily after partial isomerization by the intramolecular addition SiH to CO, to give phosphorylated siladioxane and siladioxene. The conformation of these heterocyclic compounds has been studied.     

Calculation of cross sections for positron-Ar collisions

The three-body classical trajectory Monte-Carlo (CTMC) method is used to investigate positron-argon atom collisions. The total ionization cross sections are presented along with singly and doubly differential cross sections. The existence of the cusp-like peak in the triply differential electron and positron spectra at positron impact is predicted.     

Salting-in of alcohols in aqueous solutions by tetraalkylammonium bromides at the freezing temperature

The freezing-point depression of the ternary systems tetraalkylammonium bromides-t-butanol-water for the first five homologs of R₄NBr was measured. In the case of Bu₄NBr, the effect of size of the alcohol (methahol ton-butanol) was also investigated. From the corresponding freezing-point data for the binary systems the apparent salting constants were calculated. The true salting constantsk _s were obtained by extrapolation to infinite dilution. These are all very close to zero at the freezing temperature. From the corresponding thermochemical data the temperature dependence ofk _s was calculated, and above 5°C all the R₄NBr salts int-butanol; the salting-in increases with temperature and with the size of the hydrophobic cations. The scaled-particle theory is at present the only one which can account semiquantitatively for the temperature dependence of the salting-in effect. On leave of absence from Chemistry Department, The University, Sheffield S3 7HF, England To whom correspondence should be addressed.     

Thermolyse des β-énaminodiesters cycliques: Accès à divers β-énaminoesters, β-énaminothioesters et β-enaminoamides.

A new synthesis of β-enaminoesters, β-enaminothioesters et β-enaminoamides by thermic decomposition of β-enaminodiesters is described.     

Thermodynamic properties of alkali halides. IV. Apparent molal volumes,expansibilities, compressibilities,and heat capacities in urea-water mixtures

The apparent molal volume φ_v, expansibility φ_E, compressibility φ_K, and heat capacity φ_c of NaCl were measured in urea-water mixtures, as a function of salt (<1.5m) and urea (<13m) concentrations at 25°C. At a fixed urea concentration, the transfer functions from H₂O to 3m urea are linear functions of the NaCl aquamolality. At a fixed salt aquamolality, (0.1m), the sign of the transfer functions is in the direction of a decrease in the structure-breaking effect, and the absolute values of the transfer functions tend to level off at high urea concentrations (13m). The functions φ_v, φ_E, φ_K, φ_c, and (?φ_v/?T)_p were measured for the sodium halides and alkali, bromides (chlorides in the case of φ_K) at a fixed salt aquamolality of 0.1m and fixed urea molality of 3m. The corresponding transfer functions from H₂O to 3m urea are opposite those from H₂O to D₂O and similarly are relatively independent of ionic size. This suggests that urea, shows no specific interaction affinity for ions and that the overall number of water molecules influenced by the ions is relatively constant for all alkali halides. The lithium halides are an exception in that Li⁺ seems to have hardly any structure-breaking effect.     

Beitrag zur Kenntnis der Pt(II)-Verbindungen mit Acetoxim

Zusammenfassung Es wurde die thermische Zersetzung dercis-undtrans-Isomeren des [PtAox ₂Cl₂] sowie des [PtAox ₃Cl]Cl mit Hilfe derTG-undTD-Kurven im Falle des reinen Komplexes sowie im Falle einer Mischung mit Al₂O₃ (1:3) geklärt. Dietrans-Form ist stabiler als diecis-Form, die Zersetzung wird durch Al₂O₃ nicht beeinflu\t. [PtAox ₃Cl]Cl wird infolge der Erhitzung in die stabileretrans-Form [PtAox ₂Cl₂] umgewandelt und verhält sich auch weiterhin wie diese.

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A contribution to the study of the compounds of Pt(II) with acetoxime

The thermal decomposition ofcis- andtrans-[PtAox ₂Cl₂] and of [PtAox ₃Cl]Cl was studied by means ofTGA andTDA on pure substances as well as on mixtures with Al₂O₃ (1:3). Thetrans form is more stable then thecis form, the presence of Al₂O₃ has no influence on its decomposition. The [PtAox ₃Cl]Cl is transformed by heating into the more stabletrans-isomer and its further behaviour is identical with that of thetrans isomer.

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Mit 4 Abbildung     

Regiospecifically controlled formation of tetrasubstituted tributyltin ketone enolates catalyzed by a palladium complex

The palladium-catalyzed hydrostannolysis of α-disubstituted allyl β-keto esters yields the corresponding tributyltin β-keto carboxylates which loose carbon dioxide at very moderate temperature, thus leading to the regiospecific formation of tributyltin tetrasubstituted enolates.     

Dramatic changes in geometry after ionization: experimental and theoretical studies on the electronic properties of fluorocarbonyl (mono-, di-, and tri-) sulfur compounds

In this work, we present a complete study on He I photoelectron spectroscopy (PES) for the fluorocarbonyl mono-, di-, and trisulfur compounds FC(O)SCl, FC(O)SSCH(3), and FC(O)SSSC(O)F. After optimizations of the structure for stable conformers at different levels of theory, a complete theoretical study involving the calculation of the ionization energies using orbital valence Green's functional (OVGF) was performed. Calculations of radical-cationic forms were carried out in order to compare their properties with those of the neutral molecules. The first IP values are 10.7, 9.0, and 10.5 eV for FC(O)SCl, FC(O)SSCH(3), and FC(O)SSSC(O)F, respectively. The groups bonded to the S atom mainly influence the ionizations originating from the sulfur lone pairs. A wide electronic delocalization in the FC(O)S moiety can be deduced from experimental and theoretical results, which leads to a strong energetic stabilization of the n' '(S) (sulfur lone pair pi orbital). Other conclusions relate to effects on the substituents attached to the S atom and the importance of the molecular planarity in the orbital stabilization of the FC(O)S moiety for the neutral molecules. It is worthwhile mentioning that FC(O)SCl retains its planar structure after ionization, but drastic changes occur in the geometry of both FC(O)SSCH(3) and FC(O)SSSC(O)F. The FC(O)SSCH(3) molecule adopts a heavy atom planar structure after ionization. The FC(O)SSS moiety becomes a planar form after the ionization of the FC(O)SSSC(O)F molecule, whereas the second C(O)F group maintains its original conformation with respect to the SSS group.