Electron energy loss spectroscopy of liquid glycerol

The inelastic scattering of low energy electrons from liquid glycerol has been studied. For the first time, electron energy loss spectra of liquids are sufficiently well resolved to permit the identification of vibrations corresponding to individual bonds, namely the C–H and O–H stretching vibrations in glycerol. The angular distribution of the specular peak is very broad, indicating the absence of long-range order at the surface of the liquid. The measurement of the loss signals as a function of the primary electron energy suggests a hybrid mechanism of excitation. The excitation mechanism for the O–H vibration has a stronger impact character as compared to the C–H vibration. A negative ion resonance of glycerol is found at a primary energy of 8 eV. The signal intensities measured as a function of the specular angle of the electron beam appear to be influenced by the angular dependence of the dipole and impact scattering cross-section and a possible preferred orientation of the C–H and O–H groups at the surface of the liquid.     

Ene reaction of singlet oxygen,triazolinedione, and nitrosoarene with chiral deuterium-labeled allylic alcohols: the interdependence of diastereoselectivity and regioselectivity discloses mechanistic insights into the hydroxy-group directivity

The ene reaction of singlet oxygen ((1)O(2)), triazolinedione (TAD), and nitrosoarene, specifically 4-nitronitrosobenzene (ArNO), with the tetrasubstituted 1,3-allylically strained, chiral allylic alcohol 3,4-dimethylpent-3-en-2-ol (2) leads to the threo-configured ene products in high diastereoselectivity, a consequence of the hydroxy-group directivity. Hydrogen bonding favors formation of the threo-configured encounter complex threo-EC in the early stage of ene reaction. For the analogous twix deuterium-labeled allylic alcohol Z-2-d(3), a hitherto unrecognized dichotomy between (1)O(2) and the ArNO and TAD enophiles is disclosed in the regioselectivity of the tetrasubstituted alcohol: Whereas for ArNO and TAD, hydrogen bonding with the allylic hydroxy group dictates the regioselectivity (twix selectivity), for (1)O(2), the cis effect dominates (twin/trix selectivity). From the interdependence between the twix/twin regioselectivity and the threo/erythro diastereoselectivity, it has been recognized that the enophile also attacks the allylic alcohol from the erythro pi face without assistance by hydrogen bonding with the allylic hydroxy functionality.     

EXAFS spectroscopic evidence for an Fe=O unit in the Fe(IV) intermediate observed during oxygen activation by taurine:alpha-ketoglutarate dioxygenase

The Fe(II)- and alpha-ketoglutarate-dependent dioxygenases catalyze hydroxylation reactions of considerable biomedical and environmental significance. Recently, the first oxidized iron intermediate in the reaction of a member of this family, taurine:alpha-ketoglutarate dioxygenase (TauD), was detected and shown to be a high-spin Fe(IV) complex. In this study we have used X-ray absorption spectroscopy to demonstrate the presence of a short (1.62 A) interaction between the iron and one of its ligands in the Fe(IV) intermediate but not in the Fe(II) starting complex. The detection of this interaction strongly corroborates the hypothesis that the intermediate contains an Fe=O structural motif.     

1,3-Heterocumulene-to-alkyne

Transition structures and energy barriers of the concerted prototypical cycloaddition reaction of 1,3-heterocumulenes (S=C=S, S=C=NR, RN=C=NR, and heteroanalogs) to acetylene resulting in nucleophilic carbenes were calculated by G2(MP2) and CBS-Q ab initio quantum chemical and by density functional theory (DFT) methods. According to the calculations the activation energies (activation enthalpies) of the homoheteroatomic cumulenes decrease in the order O > S > Se and NH > PH and the reaction energies in the order O > S approximately Se and PH > NH. The reaction of carbon disulfide and acetylene has a lower reaction barrier than that of carbodiimide and acetylene although the first reaction is less exothermic than the second one. The stronger cyclic stabilization of the 1, 3-dithiol-2-ylidene in the transition state is discussed in terms of deformation and stabilization energies and of bond indices. The known reactions of carbon disulfide with ring-strained cycloheptynes were examined by DFT and by DFT:PM3 two-layered hybrid ONIOM methods. In agreement with qualitative experimental findings the activation energy increases and the reaction energy decreases in the sequence S, SO(2), and SiMe(2) if CH(2) in the 5-position of 3,3,7, 7-tetramethyl-1-cycloheptyne is replaced by a heteroatom or heteroatomic group, respectively. The results of these calculations were corroborated by experimental studies with carbon diselenide and isothiocyanates as 1,3-heterocumulenes. The cycloaddition of carbon diselenide to cyclooctyne proceeded faster than with carbon disulfide, the main product being the 1,3-diselenol-2-selone. Under more drastic conditions it was possible to add methyl and phenyl isothiocyanate, respectively, to 3,3,6, 6-tetramethyl-1-thia-4-cycloheptyne. The products are 1:3 adducts (cycloalkyne:isothiocyanate) whose formation is explained by a trapping reaction of the first formed 1,3-thiazol-2-ylidenes.     

Sandwichartige Polyoxowolframate mit Indium(III) als Heteroatom — Synthese und Charakterisierung der ersten Vertreter einer neuen Familie von Anionen

Sandwich‐like Polyoxotungstates with Indium(III) as a Heteroatom — Synthesis and Characterization of the First Examples of a New Type of Anions The syntheses of three novel polyoxometalates containing indium as heteroatom are presented. The compounds are characterized by X‐ray structure analysis and vibrational spectra Na_5nH_2n[(In(H₂O)₂)_{1, 5}(Na(H₂O)₂)_{0, 5}(In(H₂O)₂)₂(SbW₉O₃₃)₂]_n · 28n H₂O ( 1 ) crystallizes in the monoclinic crystal system (C2/c) with a = 19.370(4), b = 17.852(4), c = 30.015(6) Å and β = 97.38(3)°. Na₂K₂H₂[(In(H₂O)₃)₂(In(H₂O)₂)₂(AsW₉O₃₃)₂] · 37 H₂O ( 2 ) crystallizes in the monoclinic crystal system (space group C2/m) with a = 20.323(4), b = 15.269(3), c = 16.014(3) Å and β = 94.06(3)°. Na₁₀H₂[In₄(H₂O)₂(CoW₉O₃₄)₂] · 43 H₂O ( 3 ) shows lattice constants of a = 13.047(3), b = 17.735(4), c = 21.054(4) Å and β = 93.38(3)° in monoclinic crystal system (space group P2₁/n). The heteropolyanions in 1 and 2 are examples of the so called M₂X₂M₂₀‐type. They are built up of two β‐B‐[XW₉O₃₃] fragments, which are derived from defect structures of the Keggin anion. These subunits are connected by four MO₆‐groups (with M = In^III or Na for 1 and In^III for 2 ). The heteropolyanion in 3 belongs to the M₄X₂W₁₈‐type, which contains two α‐B‐[XW₉O₃₃]‐units connected via a belt of four InO₆‐polyhedra.     

Synthese von 4(5)-acyl-5(4)-alkylimidazolen aus symmetrischen 1,3-dicarbonylverbindungen

Synthesis of 4(5)-Acyl-5(4)-alkylimidazoles from Symmetrical 1,3-Diones A new synthesis of 4(5)-acyl-5(4)-alkylimidazoles 1 is described. The symmetrical 1,3-diones 5a and 5b were reacted with N₂O₄ to give the nitro compounds 7a and 7b , respectively; 5c was treated with NaNO₂ to give the nitroso compound 7c (Scheme 2). Hydrogenation of 7a , 7b and 7c over Pd/C in acetic acid/acetic formic anhydride yielded the formamides 9a , 9b and 9c , whose cyclization in formamide/formic acid afforded the 4(5)-acyl-5(4)-alkylimidazoles 1a, 1b and 1c , respectively. Oxazoles 11a and 11b were obtained from the corresponding formamides 9a and 9b with methanesulfonic acid/P₂O₅.     

Li5B7S13 und Li9B19S33: Zwei Lithiumthioborate mit neuen hochpolymeren Anionengerüsten

Li₅B₇S₁₃ and Li₉B₁₉S₃₃: Two Lithium Thioborates with Novel Highly Polymeric Anion Networks Li₅B₇S₁₃ (C2/c; a = 17.304(2) Å, b = 21.922(3) Å, c = 12.233(2) Å, β = 134.91(1)°; Z = 8) and Li₉B₁₉S₃₃ (C2/c; a = 23.669(9) Å, b = 14.361(3) Å, c = 12.237(3) Å, β = 103.77(2)°; Z = 4) were prepared by reaction of stoichiometric amounts of lithium sulfide, boron, and sulfur at 750°C (Li₅B₇S₁₃) and 700°C (Li₉B₁₉S₃₃) with subsequent annealing. The crystal structures consist of interpenetrating, polymeric boron sulfur anion networks which are formed by corner-sharing of B₄S₁₀ and B₁₀S₂₀ units (Li₅B₇S₁₃), or B₁₉S₃₆ units (Li₉B₁₉S₃₃). The lithium cations are situated in between with a strong disorder in Li₉B₁₉S₃₃.     

Li6+2x[B10Se18]Sex (x ≈ 2), ein ionenleitendes Doppelsalz

Li_6+2x[B₁₀Se₁₈]Se_x (x ≈ 2), an Ion‐conducting Double Salt Li_6+2x[B₁₀Se₁₈]Se_x (x ≈ 2) was prepared in a solid state reaction from lithium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 800 °C. Subsequent cooling from 600 °C to 300 °C gave amber colored crystals with the following lattice parameters: space group I2/a (at 173 K); a = 17.411(1) Å, b = 21.900(1) Å, c = 17.820(1) Å, β = 101.6(1)°. The crystal structure contains a well‐defined polymeric selenoborate network of composition ([B₁₀Se₁₆Se_4/2]^6?)_n consisting of a system of edge‐sharing [B₁₀Se₁₆Se_4/2] adamantanoid macro‐tetrahedra forming large channels in which a strongly disorderd system of partial occupied Li⁺ cations and additional disordered Se^2? anions is observed. The crystal structure of the novel selenoborate is isotypic to Li_6+2x[B₁₀S₁₈]S_x (x ≈ 2) [1]. X‐ray and ⁷Li magic‐angle spinning NMR data suggest that the site occupancies of the three crystallographically distinct lithium ions exhibit a significant temperature dependence. The lithium ion mobility has been characterized by detailed temperature dependent NMR lineshape and spin‐lattice relaxation measurements.     

Neue Halogenochalkogen(IV)‐Säuren: [H3O(Benzo‐18‐Krone‐6)]2[Te2Br10] und [H5O2(Dibenzo‐24‐Krone‐8)]2[Te2Br10]

Novel Halogenochalcogeno(IV) Acids: [H₃O(Benzo‐18‐Crown‐6)]₂[Te₂Br₁₀] and [H₅O₂(Dibenzo‐24‐Crown‐8)]₂[Te₂Br₁₀] Systematic studies on halogenochalcogeno(IV) acids containing tellurium and bromine led to the new crystalline phases [H₃O(Benzo‐18‐Crown‐6)]₂[Te₂Br₁₀] ( 1 ) and [H₅O₂(Dibenzo‐24‐Crown‐8)]₂[Te₂Br₁₀] ( 2 ). The [Te₂Br₁₀]^2‐ anions consists of two edge‐sharing distorted TeBr₆ octahedra, the oxonium cations are stabilized by crownether. ( 1 ) crystallizes in the monoclinic space group P2₁/n with a = 14.520(5) Å, b = 22.259(6) Å, c = 16.053(5) Å, β = 97.76(3)° and Z = 4, whereas ( 2 ) crystallizes in the triclinic space group with a = 11.005(4) Å, b = 12.103(5) Å, c = 14.951(6) Å, α = 71.61(3)°, β = 69.17(3)°, γ = 68.40(3)° and Z = 1.