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21.
22.
Peter Ettmayer Johann Waldhart Alfred Vendl 《Monatshefte für Chemie / Chemical Monthly》1979,110(5):1109-1112
X-Ray studies of the mixed nitride phases indicate complete miscibility in all cases. Lattice parameters generally showed negative deviations from the additivity rule.
Teilauszug aus der Dissertation des Dipl.-Ing.J. Waldhart an der Technischen Universität Wien, Österreich. 相似文献
23.
A new photoaldol route to alpha-amino-beta-hydroxy carboxylic acid esters is initiated by the photocycloaddition of aromatic or aliphatic aldehydes to 5-methoxyoxazoles. The 4-unsubstituted 5-methyloxazole 1 gave the cycloadducts 8a-f in high yields and excellent exo-diastereoselectivities. Hydrolysis of 8a-f gives the N-acetyl alpha-amino-beta-hydroxy esters 9a-f, which could be subsequently converted into the corresponding Z-didehydro alpha-amino acids 10a-f. Quartenary alpha-amino-beta-hydroxy esters 12, 14, 16, 18, and 20, which are stable against dehydration, were obtained from the 4-alkylated 5-methoxyoxazoles 2-6, in most cases highly erythro-selective due to the high degree of stereocontrol (exo) at the photocycloaddition (to give 11, 13, 15, 17, and 19) level. The relative configurations of the N-acetyl alpha-amino-beta-hydroxy esters were determined by NMR spectroscopy and comparison with chiral pool-derived compounds as well as by X-ray structure determination of the ester 23, formed by hydrolysis of the cycloadduct 22, derived from photocycloaddition of propionaldehyde to the isoleucine-derived oxazole 21. 相似文献
24.
Will S Lex J Vogel E Adamian VA Van Caemelbecke E Kadish KM 《Inorganic chemistry》1996,35(19):5577-5583
The synthesis, electrochemistry, spectroscopy, and structural characterization of two high-valent phenyl sigma-bonded cobalt corroles containing a central cobalt ion in formal +IV and +V oxidation states is presented. The characterized compounds are represented as phenyl sigma-bonded cobalt corroles, (OEC)Co(C(6)H(5)) and [(OEC)Co(C(6)H(5))]ClO(4), where OEC is the trianion of 2,3,7,8,12,13,17,18-octaethylcorrole. The electronic distribution in both molecules is discussed in terms of their NMR and EPR spectroscopic data, magnetic susceptibility, and electrochemistry. 相似文献
25.
Hans-Joachim Schulz Jürgen Liebscher Peter Luger Minxie Quian Johann Mulzer 《Journal of heterocyclic chemistry》1992,29(5):1125-1132
2,4,6-Trialkyl-1,3,5-triazines 1 can selectively be mono, bis or trisiminoformylated by reaction with trismorpholinomethane 2 or chloromethylene iminium salts 3 (Vilsmeier reagents), with each alkyl substituent reacting with only one molecule of the electrophile. The resulting aminoalkenyltriazines 4, 5 and 6 are partially or fully hydrolysed to corresponding formylation products. The latter exist either in enol or in unusual acylenamine tautomeric structures 10, 12 , and 13 , depending on the number of enamine or enol units found in the molecule. Reaction of triazines 1 with chlorobenzylidene iminium salts 16 gives monoiminobenzoylation to enaminotriazines 17 . 相似文献
26.
Dr. J. Dembczyński W. Ertmer U. Johann P. Stinner 《Zeitschrift für Physik A Hadrons and Nuclei》1980,294(4):313-317
The hyperfine structure of the metastable atomic states (3d 74s)5 F 2,3,4,5 and (3d 7 4s)3 F 2,3,4 of57Fe has been measured using theABMR- LIRF method (atomic beam magnetic resonance detected by laser induced resonance fluorescence). From these measurements the following hfs constantsA of the magnetic dipole interaction have been obtained (corrected for second order effects):A(5 F 2)=55.994(7) MHzA(5 F 3)=69.632(5) MHzA(5 F 4)=78.435(4) MHzA(5 F 5)=87.246(3) MHzA(3 F 2)=143.328(4) MHzA(3 F 3)=50.602(10) MHzA(3 F 4)=13.456(5) MHz 相似文献
27.
Fazil O. Gülaar Franois Mermound F. Johann Winkler Armand Vuchs 《Helvetica chimica acta》1984,67(2):488-501
Ammonia chemical ionization (CI) mass spectra of various open-chain, cyclic and unsaturated C5- to C10-alcohols were obtained at source temperatures ranging from 60° to 250°C. The reactivity of the ammonia adduct ion MNH and its fragmentation channels are characteristic for substrate structure. Although strongly temperature-dependent, the spectra give nevertheless information on the OH-group environment as well as on the C-skeleton at any source temperature. Primary, secondary and tertiary alcohols as well as allylic and simple olefinic alcohols can be distinguished by their spectra, which show ammonium adduct ions [MNH4]+, adduct dehydrogenation ions [MNH4-H2], ammonium substitution ions [MNH4-H2O]+ and [M-OH]+-ions as the main characteristic peaks. Moreover, konfigurational assignments of stereoisomeric alcohols are possible for larger substrate-size and source-temperature ranges than with isobutane CI mass spectrometry. Homologous M NH-ions show molecular-size control of fragmentation and linear MNH-ions are less stable than branched isomers due to incomplete energy randomization. 相似文献
28.
Josef Scharf Karl Schlögl Michael Widhalm Johann Lex Werner Tückmantel Emanuel Vogel Franz Pertlik 《Monatshefte für Chemie / Chemical Monthly》1986,117(2):255-267
2,7-Dibromo-1,6-methano[10]anulene (3) and 2,9-Dibromo-syn-1,6:8,13-diimino[14]anulene (9) were quantitatively separated into their enantiomers by chromatography on triacetylcellulose (TAC) in ethanol. X-ray structure analysis (Bijvoet technique) established the chiralities (+)(R)-3 and (+)(S)-9 for the dextrorotatory enantiomers.Comparison of the CD spectra allowed the configurational assignment to further optically active [10] and [14] anulenes which were also accessible by chromatography onTAC. Conversion of (+)(R)-2-bromo-1,6-methano[10]anulene (2) into the corresponding methylester (–)-4 confirmed its previously proposed chirality (–)(R).2,7-Dibromo-1,6-oxido[10]anulene (7) and 2,9-dibromo-syn-diimino[14]anulene (9) are in contrast to the 2,9-dibromo-syn-dioxido[14]anulene (10) optically stable until 250°C. Consequently their inversion barriers are higher than 42 kcal (176 kJ) mol–1.The CD spectra of mono and disubstituted anulenes (with C1 and C2 symmetry, resp.) are compared: For the [10]anulenes theCotton effect around 330 nm seems to be specific for their configuration with a positive effect indicating (S)-chirality and vice versa. Some regularities concerning the chromatographic resolutions are discussed.
Stereochemie planar chialer Verbindungen, 10. Mitt.: Röntgenkristallstruktur und absolute Chiralität überbrückter [10]- und [14] Anulene
Zusammenfassung 2,7-Dibrom-1,6-methano[10]anulen (3) und 2,9-Dibrom-syn-1,6:8,13-diimino[14]anulen (9) wurden durch Chromatographie an Triacetylcellulose (TAC) in Ethanol quantitativ in ihre Enantiomeren getrennt. Röntgenstruktur-analyse (Bijvoet-Technik) bewies für die rechtsdrehenden Enantiomeren die Chiralität (+)(R)-3 bzw. (+)(S)-9.Ein Vergleich der CD-Spektren ermöglichte die Konfigurationszuordnung weiterer optisch aktiver [10]- und [14]Anulene, die gleichfalls durch Chromato-graphie anTAC erhalten worden waren. Umwandlung von (+)(R)-2-Brom-1,6-methano[10]anulen (2) in den entsprechenden Methylester (–)-4 bestätigte dessen schon früher vorgeschlagene Chiralität (–)(R).Dibrom-1,6-oxido[10]anulen (7) und Dibrom-diimino[14]anulen (9) sind im Gegensatz zum Dioxido[14]anulen (10) bis 250°C optisch stabil. Ihre Inver-sionsbarrieren liegen somit über 42 kcal (176kJ) mol–1.Die CD-Spektren von mono- und disubstituierten Anulenen (mit C1 bzw. C2-Symmetrie) werden verglichen: Für die [10]Anulene scheint derCottoneffekt um 330 nm konfigurationsspezifisch zu sein, wobei ein positiver Effekt (S)-Chiralität anzeigt — und vice versa. Einige Regelmäßigkeiten bezüglich der chromatographischen Enantiomerentrennung werden diskutiert.相似文献
29.
Ana Cristina Gmez-Herrero Carlos Snchez-Snchez Frdric Chrioux Jose Ignacio Martínez Jos Abad Luca Floreano Alberto Verdini Albano Cossaro Estelle Mazaleyrat Valrie Guisset Philippe David Simone Lisi Jos Angel Martín Gago Johann Coraux 《Chemical science》2021,12(6):2257
Catechols are ubiquitous substances often acting as antioxidants, thus of importance in a variety of biological processes. The Fenton and Haber–Weiss processes are thought to transform these molecules into aggressive reactive oxygen species (ROS), a source of oxidative stress and possibly inducing degenerative diseases. Here, using model conditions (ultrahigh vacuum and single crystals), we unveil another process capable of converting catechols into ROSs, namely an intramolecular redox reaction catalysed by a Cu surface. We focus on a tri-catechol, the hexahydroxytriphenylene molecule, and show that this antioxidant is thereby transformed into a semiquinone, as an intermediate product, and then into an even stronger oxidant, a quinone, as final product. We argue that the transformations occur via two intramolecular redox reactions: since the Cu surface cannot oxidise the molecules, the starting catechol and the semiquinone forms each are, at the same time, self-oxidised and self-reduced. Thanks to these reactions, the quinone and semiquinone are able to interact with the substrate by readily accepting electrons donated by the substrate. Our combined experimental surface science and ab initio analysis highlights the key role played by metal nanoparticles in the development of degenerative diseases.An antioxidant catechol transforms following intramolecular redox reactions into highly reactive oxygen species, a semiquinone and a quinone, on copper. 相似文献
30.
Kronenburg CM Rijnberg E Jastrzebski JT Kooijman H Lutz M Spek AL Gossage RA van Koten G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,11(1):253-261
(R)-[1-(Dimethylamino)ethyl]benzene reacts with nBuLi in a 1:1 molar ratio in pentane to quantitatively yield a unique hetero-aggregate (2 a) containing the lithiated arene, unreacted nBuLi, and the complexed parent arene in a 1:1:1 ratio. As a model compound, [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)] (2 b) was prepared from the quantitative redistribution reaction of the parent lithiated arene Li(C(6)H(4)CH(Me)NMe(2)-2) with nBuLi in a 1:1 molar ratio. The mono-Et(2)O adduct [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)(OEt(2))] (2 c) and the bis-Et(2)O adduct [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)(OEt(2))(2)] (2 d) were obtained by re-crystallization of 2 b from pentane/Et(2)O and pure Et(2)O, respectively. The single-crystal X-ray structure determinations of 2 b-d show that the overall structural motifs of all three derivatives are closely related. They are all tetranuclear Li aggregates in which the four Li atoms are arranged in an almost regular tetrahedron. These structures can be described as consisting of two linked dimeric units: one Li(2)Ar(2) dimer and a hypothetical Li(2)nBu(2) dimer. The stereochemical aspects of the chiral Li(2)Ar(2) fragment are discussed. The structures as observed in the solid state are apparently retained in solution as revealed by a combination of cryoscopy and (1)H, (13)C, and (6)Li NMR spectroscopy. 相似文献