Calculations of hydrogen—fluorine and fluorine—fluorine nuclear magnetic spinspin coupling anisotropies for fluorinated ethenes and benzenes oriented in liqiud crystal solvents

Spinspin coupling tensors are calculated using self-consistent perturbation theory and INDO wavefunctions, in order to estimate whether neglect of their anisotropy influences molecular dimensions deduced from the NMR spectra of partially oriented solutes. It is found that anisotropy of cis and trans and many aromatic HF couplings can be neglected but that trans FF couplings are markedly anisotropic. Comparisons are made with the limited experimental results.     

Spektralphotometrische Bestimmung des Thioharnstoffs im Mikrogrammbereich

Zusammenfassung Eine spektralphotometrische Methode zur Bestimmung von Mikrogrammengen Thioharnstoff in Gegenwart von Biuret, Cyanat, Cyanursäure, Dicyandiamid, Harnstoff, Melamin und Rhodanid wird beschrieben. Sie beruht auf der Umsetzung des Thioharnstoffs mit salpetriger Säure zu Rhodanwasserstoffsäure, die mit Brom in Bromcyan übergeführt wird. Letzteres wird mit Pyridin und Barbitursäure zu einem intensiv gefärbten, stabilen Polymethinfarbstoff umgesetzt. Störungen durch andere Cyanamidderivate und -folgeprodukte werden untersucht.

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Summary A spectrophotometric method is described for the determination of micro amounts of thiourea in presence of biuret, cyanates, cyanuric acid, dicyanodiamide, urea, melamine and thiocyanates. The method bases on the reaction of thiourea with nitrous acid to thiocyanic acid, which is converted with bromine to cyanogen bromide. The latter forms with pyridine and barbituric acid an intensively coloured, stable polymethine dye. The interferences by other cyanamide derivatives and resultant products have been investigated.

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3. Mitteilune über die Analyse der Cyanamidderivate. 2. Mitteilung siehe ¹⁴.

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Frau S. Mohs möchten wir an dieser Stelle für ihre gewissenhafte Mitarbeit unseren Dank aussprechen.     

Determination of hexamethylene-based isocyanates in spray-painting operations. Part 1. Evaluation of a polyurethane foam sponge sampler

A polyurethane foam (PUF) sponge was mounted in a cassette sampler and evaluated as a sorbent for the collection of hexamethylene diisocyanate (HDI) monomer and HDI-based oligomers. Recovery studies indicated 112 +/- 34% average recovery of HDI monomer and 92 +/- 9% and 97 +/- 25% average recovery of HDI-based oligomers when using impregnated PUF sponges. The PUF sponge was also evaluated during actual spray-painting operations. In a series of side-by-side sampling events, an impinger filled with 1-(2-methoxyphenyl)piperazine (MOP) in toluene was compared directly with a cassette sampler containing a PUF sponge impregnated with MOP or 1-(9-anthracenylmethyl)piperazine (MAP) in dimethyl sulfoxide (DMSO). For the analysis of HDI-based oligomer, there is no significant difference (p < 0.05, n = 7) in the air concentration when sampling with either the PUF sponge cassette or the impinger. The results are significant because they indicate that a PUF sponge, which is more convenient than an impinger, may be used for the collection of HDI-based oligomer generated during spray-painting operations.     

Synthesis of some pyrrolobenzothiazepines via N-aryl-2-thiocyanatopyrroles

Pyrrolo[1,2-a[3,1]benzothiazepines were successfully synthesized from alkylthiopyrroles. The latter compounds were prepared from the appropriate N-aryl-2-thiocyanopyrroles. 2,3-Dihydro-3-oxo-4-phenylthieno[3,2-b]pyrrole ( 29 ) was obtained from acid treatment of the 2-pyrrolylthioacetic acid 28 .     

Dual fluorescence (S1, S2) in chrysene and 3,4-benzophenanthrene

S₂ and S₁ fluorescence of chrysene and 3,4 benzophenanthrene has been observed in the vapour phase under collision free conditions. It is shown that the intermediate strong couplinng model can be applied to these molecules. The efficiency of the transfer of the excess energy to collision partners is given for different gases.     

Time-weighted average sampling of airborne n-valeraldehyde by a solid-phase microextration device

A solid-phase microextraction (SPME) device was used as a time-weighted average sampler for n-valeraldehyde. The SPME device was first modified to improve the wearer's acceptance as a passive sampler. Then a poly(dimethylsiloxane)-divinylbenzene fiber was used and O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) was loaded onto the fiber. Vapors of known concentrations around the threshold limit values time-weighted average of n-valeraldehyde and specific relative humidities (RHs) were generated by syringe pumps in a dynamic generation system. n-Valeraldehyde vapors in gas bags were also generated. An exposure chamber was designed to allow measurement of face velocities, temperatures, exposing vapor concentrations, and RHs. Gas chromatography with flame ionization detection was used for sample analysis. The appropriate adsorption time for SPME coating PFBHA was determined to be 2 min and the desorption time for oxime formed after sampling was optimized to be 2 min. The experimental sampling constant was found to be (3.86+/-0.13) x 10(-2) cm3/min and face velocity was not expect to have effect on the sampler.     

Die Massenspektren der Pyrrolidide einiger aliphatisch-alicyclischer Carbonsäuren

The mass spectra of the pyrrolidides of some long-chain carboxylic acids with alicyclic residues attached to their ω-end are discussed and compared with the spectra of the corresponding esters. Fragmentation triggered by the pyrrolidide group generates a series of peaks, which clearly exhibits the size and the structure of the carbon chain.     

Infrared laser induced energy transfer studies in S18O2

Vibrational energy transfer has been studied in S¹⁸O₂, following pumping of the symmetric stretch (ν₁) by a Q-switched CO₂ laser. Fluorescence from the asymmetric stretch (ν₃) is monitored as a function of time following the laser pulse. This fluorescence rises with a rate constant of 74 ± 10 ms^?1 torr^?1, and then decays with a rate constant of 3.6 ± 0.1 ms^?1 torr^?1 for the S¹⁸O₂ itself. The effect of rare gases on the rise and fall rates was also studied. The results agree well with those on S¹⁶O₂ and are consistent with a double V-V picture in which the excitation is distributed rapidly between the stretches, but is shared with the bend much more slowly. This produces molecules in which the stretches are much “hotter” than the bend, giving rise to possibilities of laser action on the stretch-to-bend transitions and mode-selective vibrational enhancement of chemical reactions. Also, new results have been derived on the kinetics of V-V processes in mixtures. V-V transfer in various isotopic mixtures of SO₂ has been studied and the kinetic analysis indicates that S¹⁸O₂ and S¹⁶O₂ exhibit the same V-V rates.     

Theoretical results for the excited states of ozone

On the basis of ab initio calculations (configuration interaction and generalized valence bond), we find eight excited states of ozone with vertical excitation energies less than 7 eV. Using these results the various experimental transitions are assigned. One state has an equilateral triangle as the minimum energy geometry (1.5 eV above the ground state).     

Zur Automatisierung der Auswertung bei der quantitativen Spektralanalyse

Zusammenfassung Die Eigenschaften der photoelektrischen und photographischen Registrierung von Spektren werden besprochen und die Bedeutung der photographischen Registrierung für die Verfahrensentwicklung und Routineanalyse von Proben wechselnder Zusammensetzung hervorgehoben. Das Programmsystem für den elektronischen Digitalrechner und verschiedene Möglichkeiten der Datenerfassung werden beschrieben. Durch diese Automatisierung der Auswertung wird gegenüber dem herkömmlichen Rechenbrettverfahren eine Beschleunigung um den Faktor 200 erreicht.

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Summary The characteristics of the photoelectric and photographic registration of spectra are discussed and the importance of the photographic registration for the development of methods and the routine analysis of samples of changing composition is emphasized. The program system for the electronic digitalcomputer and different possibilities of data collecting are described. Automating the evaluation has resulted in a speeding-up factor of 200 compared with the traditional computing board method.

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Die obige Arbeit wurde erwähnt von Herrn Dr. Pohl am 6. 10. 1964 in Düsseldorf in seinem Vortrag Erfassen und Verwerten von chemischen Daten. [Diese Z. 209, 19 (1965).]

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Außerdem wurde uns die Arbeit von Tunnicliff und Weaver, Analytical Chemistry 36, 2318 (1964), erst nach Abschluß unserer Arbeit bekannt. Die Autoren befassen sich mit einer ähnlichen Aufgabe, wobei allerdings das Problem der Linienauswahl eingehender behandelt wird als bei uns.