A molecular beam Fourier transform microwave study of 2-methylpyridine and its complex with argon: structure,methyl internal rotation and 14N nuclear quadrupole coupling

The rotational spectrum of 2-methylpyridine (α-picoline, CH₃C₅H₄N) in the two lowest levels of methyl internal rotation (m=0, ±1) has been recorded in the frequency range from 2 to 15 GHz using a molecular beam Fourier transform microwave spectrometer. The high resolution and sensitivity of this spectroscopic technique allowed resolution of hyperfine structures due to ^l4N nuclear quadrupole coupling with high accuracy and detection of the spectra of the ¹⁵N- and all ¹³C-isotopomers. These investigations considerably extend the results from an earlier study on the normal species (Dreizler, H., Rudolph, H. D., and Mader, H., 1970, Z. Naturforsch., 25a, 25); improved rotational and centrifugal distortion constants as well as all components of the ¹⁴N quadrupole coupling tensor have been obtained. Analysis of the spectra of the isotopomers yielded the ^I4N quadrupole coupling constants χ _cc and χ _aa – χ _bb (for the ¹³C species), the potential parameter V ₃ for the barrier hindering the internal rotation of the methyl group, and, in particular, r_o, r_s r _m ⁽¹⁾ and r _m ⁽²⁾ structural parameters for the molecule. In addition to the microwave studies on the monomer, we have also investigated the rotational spectrum of the weakly bound dimer of normal 2-methylpyridine with Ar. The results obtained for the quadrupole coupling constants and the hindering potential for the internal methyl rotation show that the corresponding parameters are not significantly, or only slightly, changed in the complex.     

Editorial announcement

Editorial announcement     

Envy-free rights assignments and self-oriented preferences

Very recently a new solution to Sen's “Impossibility of a Paretian liberal” has been suggested where the focus is on the rights assignments per se (Austen-Smith, 1979). It was shown that the concept of fairness, when applied to rights, admits the existence of social decision functions which satisfy Sen's original conditions. Unfortunately this result collapses when individuals have rights over more than one pair of alternatives.In order to obtain possibility results for this more general case the present paper proposes to restrict individuals' preference orderings. It is proved that envy-free collective choice rules exist if individual preferences are self-oriented and if, in addition, people attach primary importance to their own private sphere alternatives. These restrictions are quite severe, but they may be justified if one values the absence of envy in rights allocations very highly.     

Gas chromatographic-mass spectrometric investigations on lipophilic anthropogenic substances in marine organisms

Summary Methods are needed for the trace analytical identification of anthropogenic substances in marine matrices. Here we are mainly concerned with lipophilic compounds which may be enriched through food chains and, thus, represent a potential danger. Their investigation by capillary gas chromatography-mass spectrometry is difficult as it requires a very efficient previous separation from the matrix of lipids which accompany them due to their similar chemical nature. — Clean-up methods which are usual for the determination of the classical organohalogen compounds were insufficient. The ECD detector discriminates large excesses of lipids from the matrix. But the latter falsifies the mass spectra of the relevant substances completely.Several combinations of clean-up methods were checked. One of them proved to be extraordinarily effective. It consists of a liquid-liquid partitioning between dimethylformamide (DMF) and hexane followed by a reversed phase (octadecyl) partitioning. By its application, organohalogenides from commercial cod-liver oil could be separated in a capillary gas chromatograph and identified by mass spectrometry. Remarkable is that more -HCH is present than -HCH as the latter is a pesticide and the former merely its (more toxic) by-product. Similarly, DDT's are only present in minute amounts, whereas p,pDDE, the main degradation product, produced the main peak. Furthermore, various PCB's, toxaphenes and chlordanes were present in significant amounts.

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Gas-chromatographisch-massenspektrometrische Untersuchung lipophiler anthropogener Stoffe in marinen OrganismenI. Ein Verfahren zur Probenvorbereitung durch Flüssig-flüssig- und Umkehrphasen (Octadecyl)-Verteilung

Zusammenfassung Benötigt werden Methoden zur spurenanalytischen Identifizierung anthropogener Substanzen in marinen Matrices. Hier geht es vor allem um lipophile Stoffe, die im Verlauf der Nahrungsketten angereichert werden und so ein Gefahrenpotential darstellen. Ihre Untersuchung durch Capillar-Gas-Chromatographie-Massenspektrometrie ist schwierig, da sie eine vorangehende weitgehende Abtrennung von den sie aufgrund ihrer ähnlichen Eigenschaften begleitenden Lipiden voraussetzt. Die bei der gas-chromatographischen Bestimmung der klassischen Organohalogenide üblichen clean-up-Verfahren erwiesen sich als unzureichend. Der ECD-Detektor diskriminiert zwar große Lipidüberschüsse aus der Matrix. Jene verfälschen jedoch die zu gewinnenden Massenspektren völlig.Bei der Überprüfung verschiedener miteinander kombinierter clean-up-Verfahren erwies sich schließlich eine Kombination als außerordentlich erfolgreich. Sie besteht aus einer Flüssig-flüssig-Verteilung zwischen DMF und Hexan und einer Reversed-Phase-Verteilung an einer Octadecylphase. Damit konnten in handelsüblichem Lebertran vorhandene Organohalogenide chromatographisch getrennt und massenspektrometrisch untersucht werden. Bemerkenswert sind die relativ großen Mengen -HCH, einem besonders toxischen Nebenprodukt des Pesticides -HCH. (Von letzterem hingegen sind wesentlich kleinere Mengen vorhanden.) DDT's sind nur in unbedeutenden Mengen zugegen. Dafür stellt p,p-DDE, das hauptsächliche Abbauprodukt, den größten Peak überhaupt. Bemerkenswert ist ferner die deutliche Präsenz von PCB's, Chlordanen und Toxaphenen.

     

Preparation of beryllium hydride by an improved pyrolysis technique

Beryllium hydride has been produced in purities of 90–98 wt% by the controlled pyrolysis of di-t-butylberyllium etherate in hot oil. It was obtained as an amorphous solid, remarkably stable at elevated temperatures and resistant to attack by water and common organic solvents. The source of residual impurities was shown by deuterium labeling to be derived largely from incomplete pyrolysis and ether cleavage. A series of alkylberyllium homologs was subjected to the pyrolysis reaction; of these t-Bu₂Be · Et₂O gave the highest purity BeH₂.     

A proposed mechanisms for the transient suppression of bacterial luminescence by hydrogen peroxide

It has been shown previously that bacterial luminescence is reversibly suppressed in vivo and in vitro by both X-rays and hydrogen peroxide. The data presented here show that the mechanisms for this phenomenon is based on the transient oxidation of reduced flavin mononucleotide.     

When is the pseudo-best estimator blue?

Summary Linear unbiased estimation of the mean of a random variable in Hilbert space is treated in the typical case where the mean belongs to a known subspace. The best linear estimate depends on the underlying covariance operatorB ₀ of the random variable. This operatorB ₀, however, is rarely completely known, so that an auxiliary operatorB is used to compute a “pseudo-best” estimate. It is shown that the best and the pseudo-best estimates coincide, if and only ifB ₀ B ⁻¹ leavesM invariant. Applications to linear regression are to be found in the references.