Laser induced fluorencence matrix study of 1,3-difluorobenzene radical cation

Laser induced fluorescence excitation and resolved emission spectra of 1,3-C₆H₄F⁺₂ are obtained in a Ne matrix with high signal/noise despite the ion's low emission quantum yield. The ground state vibrational structure is mostly regular but that of the upper is very irregular suggesting nearly degenerate, mutually perturbing, excited states.     

Polarographic reduction of pyridinium ion in pyridine tetraethylammonium perchlorate as background electrolyte

Tetraethylammonium perchlorate, compared to lithium perchlorate as background electrolyte for the reduction of pyridinium ion in pyridine, is effective over a wider potential range, but is more difficult to obtain in a pure state; slight amounts of impurities do not, however, affect the pyridinium wave. The pyridinium wave produced in 0.1 M Et₄NClO₄ may occur at a more negative potential than the main pyridinium wave in 0.1 M LiClO₄, depending on the source of the pyridinium ion, but still appears to be due to a diffusion-controlled reduction, whose limiting current is linearly proportional to concentration; the prewave observed in LiCl0₄ background generally does not appear in Et₄NClO₄ background. Specific differences in the effect of Li(I), Na(I) and Et₄N(I) background cation appear to be due to electrocapillary phenomena and perhaps to the extent of solvation of the ions. The constancy of current for solutions containing acetic acid with added acetate, pyridinium nitrate with added nitrate, and benzoic acid with added benzoate indicate that the pyridinium reduction is independent of anion concentration.     

Studies on the ozone depletion hypothesis by chlorofluorocarbons : two-dimensional stratospheric modelling and implications for stratospheric chemistry.

A two-dimensional (2-D) model of the atmosphere including photochemistry as complete as that in advanced 1-D models, parameterized transport, diurnal effects and rayleigh scattering has been used to calculate present day altitude profiles of trace species mixing ratios.The structure and content of the model will be described and a comparison of model results with atmospheric measurements will be presented.In particular, while there had been some expectation that inclusion of latitudinal and seasonal effects would resolve certain major discrepancies for atmospheric chlorine species, the current profiles for 30 degrees latitude are qualitatively similar to 1-D model results and seasonal variations are relatively small. The principle discrepancies between 1-D model results and measurements including overstimation by the model of ClO concentrations below 30 km and understimation of HCl above 30 km are still present in the 2-D model results.The absence of change in HCl also imploies that over-estimation of HF/HCl ratio above 20 km remains a problem.The implications for model validation and ozone depletion calculations, in the view of the effect of chlorofluorocarbons, will be discussed.     

Condensed thiolane 1,1-dioxide systems. 3. Two modes of cyclization of N-substituted trans-3-chloro-4-thioureidothiolane 1,1-dioxides

Reaction of trans-3-chloro-A-aminothiolane 1,1-dioxide hydrochloride with aryl isothiocyanates gives, according to the base involved, cis-perhydrothieno[3,4-d]imidazole-2-thione 5,5-dioxides or the hitherto undescribed cis-2-aryliminoperhydrothieno 3,4-d] thiazole 5,5-dioxides.For Part 2, see [1].Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1420–1423, October, 1988.     

13C-NMR. Spectroscopy of naturally occurring substances. XXXII. Vincaleucoblastine and related alkaloids.

The total assignment of the ¹³C-shifts of the complex Vinica rosea L. alkaloids vincaleucoblastine, leurosidine and leurosine and of a synthetic isomer of the latter is presented. The structure of leurosidine is corrected and a tentative structure for the acid-catalyzed product of isomerization of leurosine is proposed.     

A convenient oxazole C-2 protecting group: the synthesis of 4- and 5-substituted oxazoles via metalation of 2-triisopropylsilyloxazoles

[reaction: see text] Metalation of oxazoles at the 4 and 5 position was achieved after regioselective C-2 silyl protection. Removal of the protecting group was then accomplished under mild conditions allowing for a straightforward preparation of C-5 monosubstituted and C-4,5 disubstituted oxazoles. The first practical C-2 protecting group of oxazoles has been demonstrated.     

Beschreibung der Ad- und Desorptionsvorgänge bei der Kompression von löslichen Tensidadsorptionsschichten

Relations are given describing the compression of adsorption layers of soluble surfactants, using models of pure diffusion, pure kinetic, and mixed diffusion-kinetic-controlled adsorption. For the compression of the adsorption layer of a mixture of soluble surfactants all models predict a relativ enrichment of the most surface active substance.     

Infrared and Raman spectral interpretations of the ferroelectric phases of NaH3(SeO3)2 and NaD3(SeO3)2

The infrared and Raman spectra of NaH₃(SeO₃)₂ and NaD₃(SeO₃)₂ have been recorded from 24 to 300°K. The interpretation, assignments, and analysis of the spectral studies are presented on the paraelectric α phase (proton disordered), ferroelectric β phase (proton ordered) and ferroelectric γ phase (proton ordered). A discussion of a newly proposed proton-triggered phase transition mechanism and a possible origin of the hydrogen-bonded OH stretching region of KH₂PO₄-type ferroelectrics is given.