A new boundary treatment: HF surface potential model applied to solid-state cluster calculations

A new boundary treatment, a Hartree–Fock (HF ) surface potential model, is proposed to deal with the surface effect in the solid-state cluster calculations using the LCAO –MO –SCF ab initio method. The surface potential arises from one or more atoms, which have no basis function and are added to the calculated cluster system. These atoms are placed in such sites so that the HF potential field of the calculated system should possess a point-group symmetry. The surface potential could be found by the corresponding HF potential using a symmetry operator. The fact that a rather symmetric electronic structure of the asymmetric cluster YBa₂CuZn₂O₇ is obtained using the HF surface potential shows that the surface effect in the cluster calculations could be neutralized to a great extent. © 1995 John Wiley & Sons, Inc.     

Chromatographic detection of scandium

Scandium was readily detected by paper chromatography using methyl acetate as the solvent and quinalizarin for the developer. The reddish-violet color formed with scandium resembled the colers obtained with thorium, titanium, zirconium and the rare earths, but the difference in R_F values gave definite separation of these elements. Positive chromatographs were obtained by using 0.01 ml of solution 0.005M respect to scandium.     

The crystal and molecular structure of the cycloadduct from an activated carbodiimide and methyl isothiocyanate

The crystal and molecular structures of the cycloadduct from isopropyl[α-(dimethylthio-carbamoyl)isopropyl]carbodiimide and methyl isothiocyanate were determined by single-crystal X-ray methods. The product was established to be 2-(1-isopropyl-3,5-dimethyl-4,6-dithioxo-hexahydro-1,3,5-triazine-2-ylidenamino)-N,N-dimethylthioisoburyramide, in which contrary to expectations based on hybridisation the heterocyclic ring adopts a boat conformation.     

Dimerer Zimtalkohol

Zusammenfassung Die Stammsubstanzen des Lignins gehören der Gruppe der p-Hydroxyzimtalkohole an. Sie werden durch wäßrige Mineralsäure polymerisiert. Um das Wesen dieser Reaktion kennenzulernen, wurde der Zimtalkohol selbst in verdünnter wäßriger Lösung der Wirkung von Säure ausgesetzt. Er bildet ein Dimeres der Konstitution VIII, die durch Abbau und Synthese bewiesen wurde. Es ist anzynehmen, daß die Polymerisation der p-Hydroxyzimtalkohole nacl, einem Schema verläuft, von dem die Dimerisation des Zimtalkohols die erste Stufe ist.Institut für die Chemie dei Holzes und der PolysaccharideKollegenA. Wacek in alter Freundschaft zum 60. Geburtstag gewidmet.K. Freudenberg.     

Conformations of the ten-membered ring in 5,10-secosteroids I. X-ray and NMR. Analysis of (E)-3 β-hydroxy-5,10-seco-1(10)-cholesten-5-one esters

X-ray structure determination of the p-bromobenzoate 2b of one of the (E/Z)-isomeric 3β-hydroxy-5,10-seco-1(10)-cholesten-5-ones confirmed the (E)-configuration proposed previously and showed the cyclodecenone ring to adopt an extended crown conformation of type A ₁ (Fig. 9). Analysis of the ¹H- and ¹³C-NMR. spectra of acetate 2a revealed that in solution the ten-membered ring of this steroid exists in at least two distinct forms, the predominant (about 85%) corresponding to the solid-state conformation of 2b (= A ₁), and the minor most likely to B ₂ (Fig. 9). From NMR. data the energy difference between the two species and the relevant activation energy were estimated. A number of conformational force field calculations using a simplified partial structural model was performed; but the computed energy differences between the various possible conformations do not reproduce the effective situation, neither in solution nor in the crystal lattice, indicating that additional effects such as the transannular interaction of the double bond with the carbonyl group may strongly influence the thermodynamic stability of the system. The conformations deduced were used to rationalize the stereochemical course of different chemical reactions of 2a .     

Simple instrument for titrimetry without visual indicators. gasometric titrations: Cerimetry,chlorometry, nitrate,nitrite, hydroxide and carbonate determination

It was shown in previous papers, that many titrimetric problems can be solved by observing the pressure change of a closed system above the solution titrated at the equivalence point. This principle was made the basis of a gasometric titration method in which the end-point is found graphically. The titrant is added to the sample solution in measured increments at fixed intervals of time and the corresponding gas pressure or volume of the system is recorded and then plotted against the volume of added titrant. Half a dozen readings are sufficient to establish the end-point of a titration, which is found at the intersection of two straight lines. This graphical method was applied to cerimetry and chlorometry, as well as to some other analytical reactions (determination of nitrite, nitrate, hydroxide and carbonate) already described in previous papers on the gas pressure end-point technique. The results are comparable in precision and accuracy to the values obtained by the conventional visual end-point titrations. A gasometric titration takes about 10 minutes. The presence of other substances in the sample capable of reacting with the titrant does not necessarily cause interference.     

13 C 183W-Kopplungen als sonde für metall—carbin-, —carbenund—alkyl-bindungen

Carbon-13 NMR data are reported for trimethyltin derivatives containing ER_n groups where E  C, Si, Ge, Sn, N, O and S including a series of cyclic amines with ring sizes from three to seven. Coupling constant values for the homologous series of fourth group derivatives give goood correlations with the electronegativity of E. The observation of the two-bond, ¦ ²J(¹¹⁹SnE¹³C) ¦ couplings only in the derivatives containing bulky R groups is rationalized by a bimolecular exchange of ER_n groups in the concentrated solutions studied.     

Vertical proton affinities of CH2O and CH2OH+ in their ground singlet,excited triplet and ionized doublet states

Vertical proton affinities were calculated with closed and open shell direct SCF-MO methods for the ground, excited triplet and ionized doublet states of CH₂O and CH₂OH⁺.The computed gas phase basicity of CH₂O follows the order: CH₂O(¹ A ₁) > CH₂O*(³ A ₁ or ³ A ₂) > CH₂O⁺(² B ₂ or ² B ₁).     

Emission,Emissionslebensdauer und Absorption von [Cr urea6]X3-Einkristallen

Emission and absorption polarization spectra as well as emission lifetimes between room temperature and 5 °K have been measured of [Cr urea₆]X₃ single crystals, where X stands for ClO ₄ ^– , J^–, NO ₃ ^– , Br^–, Cl^–, F^–, and X₃ for JSO ₄ ^3– . The strong temperature dependence of the fluorescence/phosphorescence-ratios, and of the emission lifetimes is discussed. The differences between the spectra as well as the emission lifetimes of the various salts can be attributed to an anion dependent trigonal perturbation.

Die Autoren danken dem Verband der Chemischen Industrie für finanzielle Unterstützung dieser Arbeit.     

Veronicosid,ein neues Iridoidglucosid aus Veronica officinalisL.(Scrophulariaceae)

Veronicoside, a new iridoid glucoside from Veronica officinalis L. (Scrophulariaceae) A new iridoid glucoside, Veronicoside ( 1 ) has been isolated from Veronica officinalis L. The structure of 1 has been determined by chromatographic and spectroscopic analysis as 6-benzoylcatalpol.