L3/L2 white-line intensity ratios in the electron energy-loss spectra of 3d transition-metal oxides

The L₃/L₂ white-line intensity ratio in transition-metal oxides deviates widely from the statistical value of 2 : 1 but shows interesting systematics. In a series of oxides of a given metal, the ratio reaches a maximum for the d⁵ configuration (e.g. MnO) and a minimum for the d⁰ configuration (e.g. KMnO₄). In a series of monoxides, sesquioxides and dioxides of different metals, the ratio is again a maximum at the d⁵ configuration and decreases as the configuration changes towards d⁰ or d¹⁰. Our results, obtained by electron energy-loss spectroscopy, carried out in an electron microscope, are interpreted on an atomic mechanism involving spin-spin coupling. According to this model, the L₂ transition probability decreases in the progression d⁰ to d⁵ whereas the L₃ transition probability decreases beyond d⁵.     

Lime,soda and selenium: An early example of chemical process automation

The automatic control of certain physical phenomena, such as temperature and speed of rotation, has long been commonplace. However, the means by which this form of control can be applied to a chemical process are not so obvious. A sensing system must be found to monitor the status of the particular chemical system.     

The arylation of nitroalkanes and nitronate salts with aryllead triacetates

Nitroalkanes and their nitronate salts undergo α-arylation in good yield when treated with an aryllead triacetate in dimethyl sulfoxide.     

Physico-chemical properties of iron-tin mixed oxide catalysts in cyclohexane oxidation

The state of mixed iron-tin oxide catalysts with a variable ratio of their metallic components has been studied by Mössbauer and ESCA spectroscopy. The results are compared with the activity of these catalysts in cyclohexane oxidation.

---

- . .

     

Analytical aspects of absorption spectroelectrochemistry at a platinum electrode-I Study of metal ions

An apparatus has been built with which the intensity of a light-beam passing at grazing incidence over a platinum electrode can be monitored. The absorption of light which occurs during the electrolysis of dilute aqueous metal ion solutions has been studied as a function of a number of parameters including wavelength, potential difference and concentration. The theories of metal deposition and processes occurring at the electrode surface and in the diffusion layer have been examined and a mechanism for the production of the absorbing species in terms of increase in pH of the catholyte is proposed. The analytical potential of the technique is discussed.     

Prediction of chromatographic parameters for some anilines by molecular connectivity

Summary The possible relation existing between R_F values obtained by thin-layer chromatography for a group of anilines with connectivity indices proposed by Kier and Hall has been studied. Using multivariable regression the corresponding connectivity functions, selected for their respective correlation coefficients, standard deviations, Snedecor's F and Student's t were obtained. Regression analysis of the connectivity functions gives a correct prediction of the experimental elution sequence for this group of substances on silica gel stationary phases and various mobile phases of different polarity. The corresponding random and stability studies of the different prediction models selected were carried out, showing good stability and null randomness in all cases.     

Addition dipolaire-1,3 aux olefines portant une substitution captodative: reactivite comparee des α et des β amino acrylnitriles vis a vis des arylazides.

Arylazides reacted with α amino-acrylonitriles $\text{1}$ to produce 1-aryl-5-amino-triazoles, and with β amino-acrylonitriles $\text{2}$ to give 1-aryl-4-cyanotriazoles. Kinetics showed the Hammett ρ to be > o and therefore, these reactions are controlled by LUMOazide-HOMOolefin interaction. Despite the captodative substitution in $\text{1}$ and $\text{2}$ (ΔΔ E^≠～ 500 cal.M^?1) does'nt agree with a diradical intermediate.     

The photochemical reactions of α,β,γ,δ -unsaturated diazo compounds at low temperature

The α,β:γ,δ-unsaturated tosylhydrazone lithium salts (4) undergo photolysis at ?60°C to give vinylcyclopropenes (10) and [l,2]diazeto[l,4-a] pyrroles (11) and/or (12). The formation of (11, X=H) establishes the intermediacy of (8, X=H) in the formation of the 3$\text{H}$-1,2-diazepine (9). The diazoalkene (5, X=Me) showed opposite electrocyclisation periselectivity to its thermal cyclisation and gave (11, X=Me) $\text{via}$ (8, X=Me), rather than the pyrazoles (2) and (3).     

High-performance liquid chromatographic analysis of dianhydrogalactitol in plasma by derivatization with sodium diethyldithiocarbamate.

A high-performance liquid chromatographic method is described for measuring submicrogram quantities of dianhydrogalactitol, a promising anti-neoplastic agent, in plasma. The drug is derivatized directly in plasma with sodium diethyldithiocarbamate to form a bis(dithiocarbamoyl) ester which absorbs UV light at 254 nm (am 17,000). The derivatized product is then extracted quantitatively into chloroform and separated by normal phase chromatography (muBondpak CN column). Dianhydrogalactitol concentration below 50 ng/ml of plasma can be detected in the eluent.     

Massenspektren neuer Phloroglucide,insbesondere solcher mit Valerylseitenketten

Mass spectra of phloroglucinol derivatives recently isolated from African Dryopteris species are presented. Phloroglucides with n-valeryl side chain were found in these ferns for the first time. In the mass spectra they show strong peaks corresponding to loss of propene (C₃H₆) produced by McLafferty rearrangement, as shown in model compounds. Aside of the rottleron change (discussed formerly) this must be considered in order to avoid wrong interpretation, particularly when mass spectra are used to analyse mixtures of homologues, as usually present in the plants. If valeryl side chains are present other methods must be used therefore to measure the amount or show the absence of lower homologues with acetyl side chains.