Raman scattering from Pt(CN)42− adsorbed on Pt colloids

Raman scattering from Pt(CN)₄^2? adsorbed on Pt colloids (average diameter of 16 A) is compared with the Raman signal from the same amount of Pt(CN)₄^2? in solution. The wavelength dependence of the adsorbate Raman intensity is measured from 308 to 647 nm and compared with a Lorenz/Mie calculation of the enhancement factor for the electromagnetic field intensity on the surface of a Pt sphere as a function of sphere radius and incident wavelength.     

The electronic structure of molecules by a many-body approach: V. Ionization potentials and one-electron properties of cyclopentadiene and 1-sila-cyclopentadiene-(2,4)

The valence ionization potentials (IP's) of cyclopentadiene and 1-sila-cyclopentadiene-(2,4) are studied by an ab initio many-body approach which includes the effect of electron correlation and reorganization beyond the Hartree-Fock approximation. The Hartree-Fock approximation gives the correct ordering of the IP's for cyclopentadiene but this ordering does not agree with the results of the previous experimental and theoretical studies. The ordering is 1a₂(π), 2b₁(π), 4b₂, 6a₁, 5a₁, 3b₂, 1b₁ (π), 4a₁, 2b₂, 3a₁. For sila-cyclopentadiene the ordering of the IP's is: 1a₂(π), 4b₂, 2b₁(π), 6a₁, 1b₁(π), 5a₁, 3b₂, 4a₁, 3a₁, 2b₂. The Hartree-Fock approximation is found to be incorrect with respect to the ordering of the 4b₂ and 2b₁(π) IP's. A number of one-electron properties are calculated in the one-particle approximation and compared with the available experimental data.     

Conformational preferences of 34 valence electron A2X4 molecules: An ab initio Study of B2F4, B2Cl4, N2O4, and C2O

Ab initio molecular orbital structures and energies of B₂F₄, B₂Cl₄, N₂O₄, and C₂O have been calculated for both perpendicular D_2d and planar D_2h rotamers. The experimental trend toward greater preference for the D_2d forms in going from B₂F₄ to B₂Cl₄ is reproduced. N₂O₄ favors the planar conformation, although the rotation barrier is overestimated at the theoretical levels used. The oxalate dianion is calculated to be more stable in the D_2d conformation; the experimental planar arrangement in the solid may be due to crystal packing forces. The preferences for one conformation over another are small; analysis indicates that different effects may predominate in each case: π stabilization for B₂F₄, hyperconjugation for B₂Cl₄, lone-pair interactions for N₂O₄, and electrostatic repulsions for C₂O.     

On low temperature fluorescence of perylene crystals

At low temperatures, the broad excimer fluorescence band of α-perylene crystals is replaced by a weakly structured emission at higher energy. This emission originates from a new crystal state (Y-state) which is populated independently of the high temperature excimer (E-state). Due to the temperature dependence of its first order decay rate and due to the thermally activated formation of the E-state, the Y-emission grows rapidly at temperatures below 90 K. The Y-emission differs from the fluorescence of the monomeric β-perylene at 5.5 K by its Stokes shift of 1300 cm^?1, the lack of vibronic structure, the long first order decay time of 40 ns and the absence of bimolecular annihilation indicating a localized state. The Y-state is attributed to a less relaxed pair state formed upon contraction of the dimeric crystal lattice.     

The reaction of 2-picoline N-Oxide with o-substituled benzoates and lsatoic anhydrides

The reaction of 2-picoline N-Oxide anion with o-substituted henzoates and isatoic anhydrides to give synthetically useful l-(2-methoxyphenyl)-2-(2-pyridinyl)ethanone N-oxides, I-(2-hydroxy-phenyJ)-2-(2-pyridinyl)ethanone N-oxides and I -(2-arninopheny])-2-(2-pyridinyl)ethanone N-oxides is described.     

Darstellung und Strukturen einiger N-(Tri-t-butoxysilyl)anilin-Derivate

Formation and Structures of N-(tri-t-butoxysilyl)aniline Compounds Para-substituted N-(tri-t-butoxysilyl)anilines (t-BuO)₃SiNRC₄H₄X-p, R = H, CH₃, with substituents of high electron affinity (X = CN, NO₂) were prepared by a one-pot reaction of tri-t-butoxychlorsilane, potassium t-butanolate and substituted anilines. Corresponding compounds with substituents of low electron affinity (X = OMe, H) preferably were prepared by metalation of anilines with sodium amide. Four crystal structures were determined. N-(tri-t-butoxysilyl)-p-nitro-aniline, N-methyl-(N-tri-t-butoxysilyl)-p-nitroaniline and N-(tri-t-butoxysilyl)-p-cyanoaniline crystallize at 298 K monoclinically, N-(tri-t-butoxysilyl)aniline crystallizes orthorhombically.     

Cyclopeptid-Antibiotika aus Aspergillus-Arten. Struktur der Echinocandine C und D

Cyclopeptide antibiotics from Aspergillus species. Structure of echinocandins C and D The echinocandins B, C and D are antifungal antibiotics produced by a strain of Aspergillus rugulosus. All three metabolites are closely related representing cyclic oligopeptides composed of six amino acids and a linolic acid residue in an amide linkage. The complete structure of echinocandin B ( 1 ) has recently been established by X-ray analysis. Structural assignments to the new minor metabolites C and D have now been made by hydrolytic and oxidative cleavage reactions, formation of N-acyl-α-aminoethers as well as by chemical correlations and extensive NMR. examinations. Echinocandin C ( 2 ), C₅₂H₈₁N₇O₁₅, contains 3-hydroxyhomotyrosine in the place of 3, 4-dihydroxyhomotyrosine present in 1 . Echinocandin D ( 3 ), C₅₂H₈₁N₇O₁₃, differs in two amino acids: 3, 4-dihyroxyhomotyrosine and 4, 5-dihydroxyornithine, unusual units of 1 being replaced by 3-hydroxyhomotyrosine and ornithine.     

Über die Temperaturabhängigkeit der 13C-NMR.-Spektren von Tetracarbonyl (η-(Z)-cycloocten)eisen und (Z)-cycloocten

On the Temperature Dependence of the ¹³C-NMR.-Spectra of Tetracarbonyl (η-( Z )-cyclooctene)iron and of ( Z )-Cyclooctene Reaction of (Z)-cyclooctene (1) with Fe₂(CO)₉ in pentane at 0° yielded tetracarbonyl(η-(Z)-cyclooctene)iron (2) as a yellow oil which can be stored over a longer period only at ?78°. It is shown that the title compounds ( 1 and 2 , respectively) are fluxional. The activation parameters for the conformational C-atom site exchange of (Z)-cyclooctene (1) and tetracarbonyl (η-(Z)-cyclooctene)iron (2) (in CCl₂F₂) have been determined between 113 K and 151 K for 1 and between 151 K and 205 K for 2 , respectively, by a complete line shape analysis of the temperature dependent proton noise-decoupled ¹³C-NMR. signals of the olefinic C-atom. The kinetic data and activation parameters are given in Tables 1 and 2.