Identification of alkyl-5H-6,7-dihydrocyclopenta[b]pyrazines in roasted meat flavor. Model reaction used as basis for natural product formation and new synthesis (author's transl)]

Identification of alkyl-5H-6,7-dihydrococyclopenta[b]pyrazines in roasted meat flavor. Model reaction used as basis for natural product formation and new synthesis. Seven alkyl-5H-6,7-dihydrocyclopenta[b]pyrazines have been identified in a roasted meat aroma obtained by thermolysis of the hydrosoluble flavor precursors of raw meat. Formation of these heterocyclics by condensation of hydroxycyclopentenones with aliphatic α-dicarbonyl compounds in the presence of ammonia has been confirmed by a model reaction. Alkyl-5H-cyclopenta[b]pyrazines and dicyclopenta [b,e]pyrazines are also obtained from this reaction, but have not yet been identified in roasted flavors. Preparation of the intermediates of the model reaction enabled development of an economical synthesis of 2,3,5-trimethyl-5H-6,7-dihydrocyclopenta[b]pyrazine.     

Pyrazines. 1re communication. I. Synthèse de méthyl-2-pyrazines alcoylées en 3, par condensation de l'éthylènediamine avec les dioxo-2,3-alcanes

The synthesis of eight 2-methyl 3-alkyl pyrazines by catalytic dehydrogenation of condensation products of ethylenediamine with 2,3-diketoalkanes is described.     

Pyrazines. 2ème communication [1]. II. Synthèse de dihydro-6,7-5H-cyclopenta[b]pyrazines alkylées

Alkyl-5H-6,7-dihydrocyclopenta[b]pyrazines are prepared by condensation of cyclopentenolones with alkylenediamines or of aliphatic α-diketones with 1,2-diaminocyclo pentanes. Products so obtained were dehydrogenated using palladium on activated charcoal, or copper chromite. NMR. and mass spectra are given for 21 bicyclic pyrazines and intermediates, and their IR. spectra are compared.     

Arbres minimaux d'un graphe preordonne

We study the minimal spanning trees of a connected graph G = (X,U) where U is partially preordered (or quasi-ordered). We characterize several kinds of optimal spanning trees and give conditions for existence of strongly optimal trees. Generalizations to bases of matroids (binary matroïds in part 2) are immediate. Sone of our results are given in terms of Krugdahl's dependence graphs. They imply previous results of Rosenstiehl and Gale in the case of linear orders or preorders.     

ChemInform Abstract: An ab initio Theoretical Study of the Electronic Structure of UO2+ and [UO2(CO3)3]5‐.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Conductivity of irradiated Kapton in relation to energy loss of ions and electrons

Abstract

We have studied the effects of 2.5 MeV electron irradiation and ion (C, N, F, Si and Kr) bombardment on the electrical conductivity of a polyimide (Kapton-H) with ion energies ranging between 320 keV (N) and 1.25 GeV (Kr). In this wide range of situations we have tried to sort out the respective effects of nuclear and electronic excitation energy losses.

For all ion irradiation the conductivity is found to scale with the electronic excitation absorbed dose: i.e. a power law of conductivity versus absorbed dose with an exponent around 9 is observed. At a given absorbed dose (in Gray units) the efficiency of each ion to enhance conductivity is found to be proportional to the electronic energy loss; electrons are much less efficient than ions and thus collective excitations are required to achieve this process.

The nuclear energy loss can perhaps play some role at conductivities higher than 100 Ω^?1 m^?1, but its effects are negligible in the range explored here.     

Ab initio study of a Bi3+ impurity in Cs2NaYCl6 and Y2O3: comparison of perturbative and variational electron correlation methods

Ab initio study of excitation energies and oscillator strengths for absorption towards the (3)P(1) and (1)P(1) states of the Bi(3+) ion has been performed for the Bi(3+) ion in gas phase and as a dopant of the cubic elpasolite Cs(2)NaYCl(6) and the yttria Y(2)O(3) crystal using the ab initio embedded-cluster method. The ground and excited states were computed with a relativistic spin-orbit configuration interaction approach suited for heavy elements. Electron correlation was treated in the scalar relativistic scheme with perturbative, variational, and coupled-cluster methods. Intermediate coupling is included via an effective-Hamiltonian based spin-orbit configuration interaction approach. Small-core (60 electrons) and large-core (78 electrons) relativistic effective core potentials (ECPs) have been used to describe the bismuth ion. The best match with experiment was obtained with the small-core ECP. The accuracy of excitation energies strongly depends on the electron correlation method used. The agreement between experimental data and the results obtained using second-order multiconfigurational perturbation theory is greatly improved with the shifted zeroth-order Hamiltonian proposed by Ghido et al. [Chem. Phys. Lett. 396, 142 (2004)]. Although quite time consuming, coupled-cluster and variational methods yield good agreement with experimental data. The first absorption band recorded for the doped elpasolite crystal is positioned with an excellent accuracy while the computed energy of the second absorbing manifold is in poorer agreement with experimental data. This suggests that interactions with neglected close-lying excited states with a ligand-to-metal charge transfer character may be significant. Calculations of the spectrum of Bi(3+) doping yttria in both the S(6) and C(2) site symmetries indicate that the absorbing manifold arises from electronic excitations localized on the Bi(3+) doping ion with main triplet 6s6p character. Our results predict the first absorbing peak to lie about 0.5 eV lower for the S(6) sites than for the C(2) site, thus attributing the violet and the green emission wavelengths to the S(6) and C(2) sites, respectively. A subsequent study of Stokes shift and emission wavelength should hopefully lead to a final assignment of the measured excitation spectra.     

Ab initio CI study and vibronic analysis of the photoelectron spectra of formaldoxime

The photoelectron spectrum of formaldoximie, CH₂NOH, has been re-investigated with higher resolution and interpreted by, means of ab initio SCF Cl calculations. Calculations have confirmed that the states increase in energy as π₁ < n₁ < π₂ < n₂ and have shown the existence of a shake-up peak at ≈15 eV. The calculation of Franck-Condon factors allowed the interpretation of the observed vibrational structure.