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  • 1
    Electronic Resource
    Electronic Resource
    Separation of Positional Isomers on A, C- and A,D-Bridged Calix[6]arene as Stationary Phases in Capillary GC (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 679-682 
    Details
    ISSN: 0935-6304
    Keywords: A,C- and A,D-bridged calix[6]arene ; stationary phase ; capillary gas chromatography ; geometric and positional isomer separation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A,C-Bridged (ACCX) and A,D-bridged isopropyldimethylsilylcalix[6]arene (ADCX) dissolved in OV-1701 were used as stationary phases in isothermal capillary gas chromatographic separation of some positional isomers. Retention factors and separation factors for the isomers were measured. The isomers investigated are well resolved on the two phases. Retention of all the solutes investigated is longer on ACCX than on ADCX. The longer retention on A,C-bridged calix[6]arene is probably due to extra inductive interactions of the solute molecule with the carbonyl moieties in the phase. Separation factors for closely eluting isomer pairs are similar on the two phases. This seems to indicate that the carbonyl moieties do not play an appreciable role in discriminating the isomer molecules on entering the cavity of the calixarene if the solute is retained by the inclusion process.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Proton-transfer reactions within ionized methanol clusters: Mass spectrometric and molecular orbital studies (1995)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 30 (1995), S. 969-976 
    Details
    ISSN: 1076-5174
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Proton-transfer reactions that proceed within methanol cluster ions were studied using an electron impact time-of-flight mass spectrometer. When CH3OH seeded in helium is expanded and ionized by electron impact, the protonated species, (CH3OH)nH+, are the predominant cluster ions in the low-mass region. In CH3OD clusters, both (CH3OD)nH+ and (CH3OD)nD+ ions are observed. The ion abundance ratios, (CH3OD)nH+/(CH3OD)nD+, show a tendency to decrease as the methanol concentration increases, which is apparently related to the cluster structure and reaction energetics. The results suggest that the effective formation of (CH3OD)nH+ ions at low concentration of CH3OD in the expansion is the result of the relatively facile rotation of methanol molecules within the smaller clusters that tend to form at low CH3OD concentration. Ab initio molecular orbital calculations were carried out to investigate the rearrangement and dissociative pathways of ionized methanol dimer. Ion-neutral complexes, [CH3OH2+…O(H)CH2] and [CH3OH2+…OCH3], are found to play an important role in the low-energy pathways for production of CH3OH2+ + CH2OH (and OCH3) from ionized methanol dimer.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jms.1190300706
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  • 3
    Electronic Resource
    Electronic Resource
    Electron impact ionization of ethylene-methanol heteroclusters: Stable configurations and mechanisms in intracluster ion-molecule reactions (1993)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 28 (1993), S. 931-939 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions that proceed within mixed ethylene-methanol cluster ions were studied using an electron impact time-of-flight mass spectrometer. The ion abundance ratio, [(C2H4)n(CH3OH)mH+]/[(C2H4)n(CH3OH)m+], shows a propensity to increase as the ethylene/methanol mixing ratio increases, indicating that the proton is preferentially bound to a methanol molecule in the heterocluster ions. The results from isotope-labelling experiments indicate that the effective formation of a protonated heterocluster is responsible for ethylene molecules in the clusters. The observed (C2H4)n(CH3OH)m+ and (C2H4)n(CH3OH)m-1CH3O+ ions are interpreted as a consequence of the ion-neutral complex and intracluster ion-molecule reaction, respectively. Experimental evidence for the stable configurations of heterocluster species is found from the distinct abundance distributions of these ions and also from the observation of fragment peaks in the mass spectra. Investigations on the relative cluster ion distribution under various conditions suggest that (C2H4)n(CH3OH)mH+ ions with n + m ≤ 3 have particularly stable structures. The result is understood on the basis of ion-molecule condensation reactions, leading to the formation of fragment ions, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_2=\!=\mathop {\rm O}\limits^ + {\rm CH}_3 $\end{document} and (CH3OH)H3O+, and the effective stabilization by a polar molecule. The reaction energies of proposed mechanisms are presented for (C2H4)n(CH3OH)mH+(n + m ≤ 3) using semi-empirical molecular orbital calculations.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210280902
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  • 4
    Electronic Resource
    Electronic Resource
    Über die Darstellung symmetrischer Tetraaryläthane und deren Fähigkeit zur Dissoziation in Radikale (1964)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 97 (1964), S. 349-362 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: symm. Tetra-pyrenyl-(3)-äthan (III), symm. Di-pyrenyl-(3)-diphenyl-äthan (VII), 2.3-Di-[pyrenyl-(3)]-butan (IX), 2.2.5.5-Tetramethyl-3.4-diphenyl-3.4-di-[pyrenyl-(3)]-hexan (X) und Hexa-pyrenyl-(3)-äthan (XI) wurden dargestellt und ihre Fähigkeit zur Dissoziation in Radikale bei Raumtemperatur mit Hilfe der Elektronenspinreasonanz -Method (ESR) untersucht. Mit Ausnahme von 2.3-Di-[pyrenyl-(3)]-butan sind sämtliche der untersuchten Verbindungen bei Raumtemperatur partiell, das Hexa-[pyrenyl-(3)]-äthan erwartungsgemäß quantitativ dissoziiert. Beim symm. Tetra-α-naphthyl-äthan (VIII) ist dagegen keine Radikaldissoziation nachweisbar. - Das von Pyren ausgehend in guter Ausbeute in zweistufiger Synthese darstellbare symm. Tetra-pyrenyl-(3)-äthan ist im organischen Solvens bei Raumtemperatur unlöslich. Es ist im festen Zustand zu 0.0025% in Radikale dissoziiert. - Die Abhängigkeit der Carbonylfrequenz im IR-Spektrum von Mono- und Diarylderivaten des Formaldehyds vom Kondensationsgrad des Arylrestes wurde untersucht.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19640970207
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  • 5
    Electronic Resource
    Electronic Resource
    Konfigurations-, Konformations- und Substituenteneinflüsse auf die (1971)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 104 (1971), S. 1147-1154 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Influences of Configuration, Conformation, and Subtituents on the 13C Chemical Shifts in Glycosides 6. Mitteil. über Fourier-Transform-13C-NMR-Spektroskopie: 5. Mitteil.: W. Voelter, G. Jung, E. Breitmaier und E. Bayer, Z. Naturforsch. 1971, im Druck.The pulse Fourier transform 13C n.m.r. spectra of 20 methyl and aryl glycosides are discussed. Configurational and conformational assignments can be made using the 13C chemical shifts of these compounds. Anomeric glycosides can be easily distinguished following this method.
    Notes: Die Impuls-Fourier-Transform-13C-NMR-Spektren von 20 Methyl- und Arylglykosiden werden diskutiert. Ihre Konfiguration und Konformation kann aus den 13C-chemischen Verschiebungen zugeordnet werden. Auch anomere Glykoside lassen sich auf diese Weise leicht unterscheiden.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19711040418
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  • 6
    Electronic Resource
    Electronic Resource
    Vier Synthesewege zu (2-Pyrimidinylamino)-n-alkansäuren (1975)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 108 (1975), S. 862-874 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Four Routes for the Synthesis of (2-Pyrimidinylamino)-n-alkanoic AcidsNucleotide analogues of amino acids with variously substituted 2-pyrimidinyl side chains are available by four synthetic routes. 1) The cyclocondensation of 2-alkyl-3-aminoacroleins (4) with amino acids containing guanidino functions (5b) gives Nδ-(5-alkyl-2-pyrimidinyl)ornithine derivatives (7). 2) Cyclocondensations of 1,3-diketones of (9) with C-(guanidino)amino acids or N-(amidino)amino acids (5a-d) yield (4,6-dialkyl-2-pyrimidinylamino)-n-alkanoic acids (10). 3) (4-Alkyl-6-oxo-1,6-dihydro-2-pyrimidinylamino)-n-alkanoic acids (13) are obtained by way of cyclocondensation of ethyl acetoacetate (12) with 5a-c. 4) The nucleophilic substitution of 2-ethylthio-6-oxo-1,6-dihydropyrimidines (14, 17) by mono- and diamino acids (15) yields (5-alkyl-6-oxo-1,6-dihydro-2-pyrimidinylamino)- and (4-alkyl-6-oxo-1,6-dihydro-2-pyrimidinylamino)-n-alkanoic acids (16, 18).
    Notes: Nucleotid-analoge Aminosäuren mit verschieden substituierten 2-Pyrimidinyl-Seitenketten sind auf vier Wegen zugänglich: Die Cyclokondensation von 2-Alkyl-3-aminoacroleinen (4) mit Aminosäuren mit Guanidinofunktion (5b) führt zu Nδ-(5-Alkyl-2-pyrimidinyl)ornithin-Derivaten (7). Cyclokondensationen von 1,3-Diketonen (9) mit C-(Guanidino)aminosäuren bzw. N-(Amidino)aminosäuren (5a-d) liefern (4,6-Dialkyl-2-pyrimidinyiamino)-n-alkansäuren (10). Durch Cyclokondensationen von Acetessigester (12) mit 5a-c sind (4-Alkyl-6-oxo-1,6-dihydro-2-pyrimidinylamino)-n-alkansäuren (13) darstellbar. Aus 2-Äthylthio-6-oxo-1,6-dihydropyrimidinen (14, 17) lassen sich durch nucleophile Substitution mit Mono- und Diaminosäuren (15) (5-Alkyl-6-oxo-1,6-dihydro-2-pyrimidinylamino)- sowie (4-Alkyl-6-oxo-1,6-dihydro-2-pyrimidinylamino)-n-alkansäuren (16, 18) erhalten.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19751080319
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  • 7
    Electronic Resource
    Electronic Resource
    Synthese von 6-(Pyrido[2,3-d]pyrimidin-8-yl)hexansäuren (1974)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 107 (1974), S. 2537-2543 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis of 6-(Pyrido[2,3-d]pyrimidin-8-yl)hexanoic AcidsBy way of nucleophilic substitution, 4-chlorouracil (8) reacts with 6-aminohexanoic acids (9,10) to yield 6-(4-pyrimidinylamino)hexanoic acids (4,5). These undergo cyclocondensation with 3-amonoacroleins and 2-(hydroxymethylene)cycloalkanones (2), respectively, to yield 6-(pyrido[2,3-d]pyrimidin-8-yl)hexanoic acids (6,7). The 1H and 13C n. m. r. spectra of these carboxylic acids substituted with heterocycles are discussed.
    Notes: Aus 4-Chloruracil (8) und 6-Aminohexansäuren (9,10) entstehen durch nucleophile Substitution 6-(4-Pyrimidinylamino)hexansäuren (4,5). Diese cyclokondensieren mit 3-Aminoacroleinen bzw. 2-(Hydroxymethylen)cycloalkanonen (2) zu 6-(Pyrido[2,3-d]pyrimidin-8-yl)-hexansäuren (6,7). Die 1H- und 13C-NMR-Spektren dieser heterocyclisch substituierten Carbonsäuren werden diskutiert.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19741070812
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  • 8
    Electronic Resource
    Electronic Resource
    Synthese optisch aktiver α-Aminosäuren mit 8-Azapurinyl-Seitenkette (1975)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 108 (1975), S. 1111-1117 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis of Optically Active α-Amino Acids Substituted in the Side Chain with an 8-Azapurinyl Residue4-Amino-6-chloro-5-nitropyrimidine (1) or 4-chloro-5-nitro-6-oxo-1,6-dihydropyrimidine (4) react with Nα-benzyloxycarbonyl-L-lysine (2a) or 6-aminohexanoic acid (2b) to give 6-(4-pyrimidinyl-amino)hexanoic acids (3a, b, 5a, b). Reduction of their nitro group and subsequent cyclization with sodium nitrite in acidic medium yields the corresponding (triazolo[4,5-d]pyrimidine-3-yl)hexanoic acid derivatives (7a, b, 9a, b). The amino acid derivatives 7a and 9a are hydrogenated to optically active 8-azapurinyl substituted α-amino acids (10, 11).
    Notes: Durch Umsetzung von 4-Amino-6-chlor-5-nitropyrimidin (1) bzw. 4-Chlor-5-nitro-6-oxo-1,6-dihydropyrimidin (4) mit Nα-Benzyloxycarbonyl-L-lysin (2a) bzw. 6-Aminohexansäure (2b) lassen sich 6-(5-Nitro-4-pyrimidinylamino)hexansäuren (3a, b, 5a, b) darstellen. Nach Reduktion der Nitrogruppe mit Natriumdithionit werden diese mit Natriumnitrit in essigsaurem Medium zu (Triazolo[4,5-d]pyrimidin-3-yl)hexansäure-Derivaten (7a, b, 9a, b) cyclisiert. Die Aminosäure-derivate 7a und 9a können zu optisch aktiven, 8-azapurinyl-substituierten α-Aminosäuren (10, 11) hydriert werden.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19751080416
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  • 9
    Electronic Resource
    Electronic Resource
    Aciditätsbestimmung mit Hilfe aliphatischer Diazoverbindungen, III. Die dynamische Acidität sehr starker Säuren (1966)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 99 (1966), S. 1704-1711 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In Ergänzung der II. Mitteilung wurden mit Hilfe säurestabiler Diazoverbindungen die Protonenaktivitäten starker und sehr starker Säuren (bis zur Chlorsulfonsäure) bestimmt, sowie diese Säuren nach Ermittlung der Säureempfindlichkeitskonstanten der Diazoverbindungen an die früher aufgestellte dynamische Aciditätsreihe nach oben angeschlossen. Dadurch konnte der der Messung zugängliche lückenlose Aciditätsbereich auf nunmehr ca. 16 pk-Einheiten erweitert werden.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19660990538
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  • 10
    Electronic Resource
    Electronic Resource
    NMR- und IR-Spektren von Oxoniumsalzen (1965)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 98 (1965), S. 3748-3756 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die NMR- und IR-Spektren einer Reihe von sekundären und tertiären Oxoniumsalzen (sowie einiger Vergleichsverbindungen) werden im Hinblick auf die chemische Verschiebung der verschiedenen Protonensignale und auf den Nachweis sehr stabiler Protonenbrücken in den Ätheraddukten der sekundären Oxoniumsalze diskutiert.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19650981142
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