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  • 1
    ISSN: 1434-4475
    Keywords: Conformational analysis ; Lanthanide induced shift ; NMR, coalescence ; Optical activity ; Rotational barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Complexation of methyl 3-nitro-2-(o-tolyl)-benzoate (2, ano-trisubstituted biphenyl) with hexacarbonyl chromium gave the isomeric Cr(CO)3 complexes3 and4 both existing as two torsional isomersa andb, as seen by nmr. For the main product3 the preferred conformations of the two torsional isomersa andb were deduced by the lanthanide induced shift (LIS) technique. The activation energy for the interconversion process could be determined from kinetic measurements and especially from1H-nmr coalescence temperature of the methylsignals. The barrier of 91±1.5 kJ/mol (21.7±0.3 kcal/mol) in3 reflects the interaction of theo-H-atom of the benzene ring passing the Cr(CO)3 moiety of the benchrotrene ring during the interconversion. A partial optical resolution of3 was achieved by asymmetric reduction with a chiral lithium-aluminium hydride yielding (+)-3 with [α] D 20 +30° (benzene) and the levorotatory alcohol (−)-7.
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  • 2
    ISSN: 1434-4475
    Keywords: Configurational correlation ; 5-Ethylindanes ; 1 H-nmr spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Starting from (+) (2R) methyl 5′-ethyl-2,2′-spirobiindane-5-carboxylate of known enantiomeric purity 79 optically active, configurationally correlated 5,5′,6′-trisubstituted 2,2′-spirobiindanes (2–7) were prepared for the purpose of testing a “shortened polynomal Ansatz” for chirality functions. Their optical rotations and1H-nmr spectra are reported. In this context several 6-substituted 5-ethylindanes (1) were prepared as model compounds for synthetic transformations.
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  • 3
    ISSN: 1434-4475
    Keywords: Ligand parameters ; chirality function ; 2,2′-Spirobiindanes ; 5,5′-disubstituted
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In order to test the semiempirical value of chirality functions in their mathematically most simple form 23 new optically active 5,5′-disubstituted 2,2′-spirobiindanes1 of known chirality and enantiomeric purity were prepared. Thus a set of about hundred compounds is now available with altogether sixteen types of ligands (i.e. substituents including hydrogen); the experimental molar rotation of fifteen compounds is used to determine the value of a ligandspecific parameter occuring in the used chirality polynomial. According to theory this polynomial is an approximation for the total rotation of derivatives with ligands of three different types and it approximates an experimentally separable part of the rotation as far as compounds with four different ligands are concerned. The additional chirality component, occurring exclusively in the case of derivatives with four different types of ligands turns out to be relatively small but not vanishing. Accordingly, the molar rotation predicted by our method is very good for disubstituted spirobiindanes of type1 and rather good for others with three different types of ligands but is distinctly worse for those with four different ligands. The numerical trend, however, is clearly represented even in cases where our calculation in principle refers to a part of the phenomenon only and the predicted absolute configuration is in call cases in agreement with the experiment. An adequate criterion to judge the quality of our approximation is introduced.
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  • 4
    ISSN: 1434-4475
    Keywords: Benchrotrenes ; Hydrogen bridges, intramolecular ; Lactone of 2′-hydroxymethyl-biphenyl-2-carboxylic acid, mono and bis tricarbonylchromium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Mono and bis tricarbonylchromium complexes of diphenic acid and its monomethylester (3, 4, 15, 16) were prepared by treating the corresponding methyl and trimethylsilylesters (e.g.12) with Cr(CO)6 and subsequent hydrolysis of the complexes1, 2, 13, and14. Diborane reduction of the carboxylic acids gave hydroxymethyl derivatives, amongst which the diol8 a is a key substance for configurational analyses by1H-nmr and ir spectroscopy. In this context monosubstituted biphenyl complexes (9–11) were prepared as reference substances. Complexation of the lactone23 of 2′-hydroxymethyl biphenyl-2-carboxylic acid afforded (besides two isomeric monocomplexes) mainly thetrans-biscomplex26 b, a key intermediate for ring opening and cyclization reactions. The stereochemical possibilities of the biscomplexes are discussed. The “racemate” configuration is preliminarily assigned to diphenic acid bistricarbonylchromium and its derivatives.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Monatshefte für Chemie 112 (1981), S. 91-104 
    ISSN: 1434-4475
    Keywords: Chromatographic Resolution on Acetylcellulose ; Circular Dichroism ; 1,3-Diferrocenylbutadienes ; 1,3-Diferrocenylpropanes ; 1,3-Diferrocenylpropenes ; 1,3-Diferrocenylpropenols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The title compound 2 was prepared by thermal dehydration of 1,3-diferrocenyl-1,3-diphenyl-propenol (24) with 70% yield.24 was accessible from 1,3-diferrocenyl-propanedione-1,3 (25) in two steps with 10% overall yield: Treatment of25 with phenyllithium gave 1,3-diferrocenyl-3-phenyl-propenone (8) which after repeated reaction with phenyllithium afforded24. Partial optical resolution of2 was achieved by chromatography on triacetyl cellulose in ethanol, whereby both (+)- and (−)-2 were obtained with different enantiomeric purities as could be deduced from the CD-spectra with Δε-values of +0.18 and −1.64, resp., at 480 nm. Attempts to prepare 1,3-diferrocenyl-allene and 1,3-diferrocenyl-1-phenyl-allene failed. In this context several 1,3-diferrocenyl-propenols,-propenones,-propenes,-propanones,-propanes and-butadienes were obtained.
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  • 6
    ISSN: 1434-4475
    Keywords: 1,2-Diferrocenylbutane (racemic and meso) ; 1,2-Diferrocenyl-1,2-diphenylethane (racemic and meso) ; Tetraferrocenylethane ; Conformations ; 13C-nmr spectroscopy ; X-ray crystal structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract X-ray crystal structure analyses of stereoisomeric 1,2-dimethyl and diphenyl 1,2-diferrocenyl ethanes (1,2) as well as of 1,1,2,2-tetraferrocenyl ethane (3) showed that racemic (threo) and meso (erythro)2 adopt conformations with antiperiplanar arrangement of the ethane H-atoms (andC 2 andC i symmetry, resp.), whereas1 and3 prefer the synclinal (skew) conformations. In3 the torsional angle between the ethane H-atoms is increased to appr. 90°;3 represents a chiral structure withC 2 symmetry. For the conformation of tetraferrocenyl ethane (3) in solutionC 2 symmetry could be deduced from the13C-nmr. spectra. The conformations of the diferrocenyl ethanes are discussed and compared with those of corresponding alkyl and aryl ethanes.
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  • 7
    ISSN: 1434-4475
    Keywords: Triacetylcellulose ; Recycling technique ; Enantiomeric purity ; Metallocene chirality ; Axial chirality ; Conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Chiral title compounds have been resolved by medium pressure liquid chromatography (MPLC) on triacetylcellulose in ethanol. Whereas a quantitative separation was achieved for16 and20, a recycling technique had to be applied to1,4,6,10 and15 leading to a 100% e.e. for1,6 and15 and to ca. 60% e.e. for4 and10. An unambiguous assignment of the chirality (+)-(R) a -(S) m for tricarbonylchromium-6,6′-dimethyl-diphenicacid dimethylester (4) was deduced both from the photochemical decomplexation to (-)-5 with the known chirality (R) a (whose e.e. was determined by MPLC on triacetylcellulose) and by comparison of the1H-n.m.r. spectra of4 and5 thereby proving the structure 4 for the former. Other chiralities both for mono and bis(tricarbonylchromium)biphenyl complexes were established by chemical correlations and comparison of the CD spectra with those of key compounds.
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  • 8
    ISSN: 1434-4475
    Keywords: Bijvoet method, Chemical and chiroptical correlation ; Circular dichroism ; Enantioselective chromatography ; 10,10′-Dibromo-2,2′-bi(1,6-methano[10]annulenyl) ; Torsional isomers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die absolute Chiralität des rechtsdrehenden (als Hauptmenge im Gemisch vorliegenden) Rotamers von 10,10′-Dibrom-2,2′-bi(1,6-methano[10]annulenyl) (1 b) (erhältlich durch Tieftemperatur-Chromatographie oder Kristallisation des (+)-Enantiomers von1 b) wurde durch Röntgenstrukturanalyse (Bijvoet-Methode) als (+)-(R) p (R) a (R) p ermittelt. Dieses Ergebnis konnte durch Reduktion von (+)-1 b bestätigt werden: Sie führte zu einem rechtsdrehenden 2,2′-Bi(1,6-methano[10]annulenyl) (1 a), das seinerseits durch Kupplung von (−)-2-Brom-1,6-methano[10]annulen (3) bekannter Chiralität (S) p erhalten wurde (und auch durch enantioselektive Chromatographie von1 a an Triacetylcellulose in Ethanol zugänglich ist). Diese Korrelation legt auch die Chiralität des (+)-Enantiomers von racem.1 a als (S) p (S) p fest. Nach den Röntgenstrukturanalysen des (Haupt)-Rotationsisomers von (+)-1 b und der Mesoform (2 b) liegen im Kristall Konformere vor, in denen die Bromatome den CH2-Brücken nahekommen. Die Torsionswinkel um die 2,2′-Bindung variieren von 33° über 53° bis 65° für (+)-1 b, racem.1 b und meso2 b.
    Notes: Summary The absolute chirality of the dextrorotatory main rotamer of 10,10′-dibromo-2,2′-bi(1,6-methano[10]annulenyl) (1 b), obtained by low temperature chromatography or by crystallisation of the (+)-enantiomer of1 b, was established by observation of anomalous X-ray diffraction as (+)-(R) p (R) a (R) p -1b. This result was confirmed by reduction of (+)-1 b to a dextrorotatory 2,2′-bi(1,6-methano[10]annulenyl) (1 a), which in turn was accessible by coupling of (−)-2-Bromo-1,6-methano[10]annulene (3) of known chirality (S) p and, moreover, by enantioselective chromatography of1 a on triacetyl cellulose in ethanol. This correlation determines also the chirality of (+)-1 a as (S) p (S) p . According to the X-ray analyses the main rotamer of (+)-1 b and the meso-form (2 b) adopt crystal structures in which the bromine atoms come close to the CH2-bridges. The torsional angles around the 2,2′-bonds vary between 33°, 53° and 65° for (+)-1 b, racem.1 b and the mesoform2 b, respectively.
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  • 9
    ISSN: 1434-4475
    Keywords: Circular dichroism ; Chemical and chiroptical correlation ; Enantioselective chromatography ; Torsional isomers and barriers ; X-ray crystal structures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Titelverbindung2 wurde durch Hochdruckreaktion von 1,1′-Bianthryl mit Ethylen oder durch Kupplung von 1-Brom-9,10-dihydro-9,10-ethano-anthracen (4) als Mischung der Diastereomeren (Mesoform2a und Racemat2b) im Verhältnis von 1.5:1 bzw. 2.3:1 erhalten. Die konfigurative Zuordnung erfolgte sowohl aus den1H- und13C-NMR-Spektren als auch durch Kupplung von linksdrehendem4 zu (−)-2 b. Optisch aktives4 war durch enantioselektive Chromatographie an Triacetylcellulose in Ethanol optisch rein zugänglich. Seine Konfiguration wurde durch Umwandlung in die entsprechende Carbonsäure5 (bekannter Chiralität) als (+)(9R) [bzw. (−)(9S)] bestimmt. Damit war auch die Zentrochiralität im erwähnten Kupplungsprodukt (−)-(2b) als (9S)(9′S) festgelegt. Das Racemat2b ist eine Mischung von Rotameren im Verhältnis von 1.8:1. Die Rotationsbarriere wurde (in Abhängigkeit von der Temperatur) als ΔG#=92−95 kJ mol−1 sowohl durch1H-NMR-als auch CD-Kinetik (basierend auf der Äquilibrierung der getrennten optisch aktiven Rotameren vonracem.2) ermittelt. Für die letzteren können aufgrund der Annahme bevorzugter Konformationen auch die Symbole für die Axialchiralität vorgeschlagen werden. Für (−)-2b: (9S)(R)a(9′S) für das überpopulierte bzw. (−)-(9S)(S)a(9′S) für das unterpopulierte Rotamer. Diese Annahmen wurden durch Röntgenstrukturanalysen von2a und des Hauptrotamers von2b (mit Torsionswinkeln von −111.1 bzw. −121.2°) bestätigt.
    Notes: Summary The title compound2 was prepared either by highpressure reaction of 1,1′-bianthryl with ethylene or by coupling of 1-bromo-9,10-dihydro-9,10-ethanoanthracene (4). Both syntheses afforded a mixture of diastereoisomers (meso2a and racemate2b) in a ratio of 1.5:1 and 2.3:1, respectively. Configurational assignment was possible both from the1H- and13C-NMR spectra and by coupling of laevorotatory4 (accessibly by enantioselective chromatography on triacetyl cellulose in ethanol) to laevorotatory2b. (+)-4 was tranformed into the dextrorotatory carboxylic acid (+)-5 of known configuration (9R) thus establishing the configuration of (+)-4 as (9R) too and hence the centrochirality in (−)-2b as (9S)(9′S). The racemic form2b is a conformational (appr. 1.8:1) mixture of two rotamers. The rotational barrier was established as ΔG #=92−95 kJ mol−1 (depending on the temperature) both by1H-NMR and CD kinetics (based on equilibration of the separated optically active rotamers ofracem.2). For the latter preferred conformations were assumed allowing the assignment of the axial chirality: e.g. (−)-(9S)(R)a(9′S) for the main rotamer of (−)-2 b [and (−)(9S)(S)a(9′S) for the underpopulated one]. All assumptions were confirmed by X-ray crystal structure analyses of2 a and the main rotamer of2b with torsional angles around the 1,1′-bonds of −111.1 and −121.2°, respectively.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Monatshefte für Chemie 106 (1975), S. 229-259 
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Reduction (both catalytically and with complex hydrides) of the diphenyl diketones1 (a, b, c andd withn=0, 2, 3 and 4) was investigated mainly with regard to the diastereomeric ratio of the diols2. For2 a and2 b exact results were obtained by NMR spectroscopy (without or with shift reagents) of the diol mixture (2 a) or after stereoselective cyclization to the cyclic ethers (3 b). AlsoGC andLLC were employed for the analysis of2 a (GC of the trimethylsilyl derivatives) and for the ethers3, resp. (GC for3 a and3 d;LLC for3 b and3 c). The reduction of1 a, 1 b (and in part1 c) proceeds with high stereoselectivity; themeso-diol preponderates in the case of2 a, therac.-diol for2 b and2 c; with increasingn the diastereomeric ratio approaches the statistical ratio of 1∶1. Preparations of the stereoisomeric diols (2 b, c andd via acetylenic precursors) and of the cyclic diphenyl ethers (by stereoselective cyclization and/or chromatographic separation;3 c and3 d for the first time) as well as the determination of their configurations are described. The latter was achieved by NMR and for the ethers3 also by hydrogenation of the corresponding heteroaromatics.
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