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  • 1
    Electronic Resource
    Electronic Resource
    Ringdeformationen und rotameres Verhalten des Phenylrestes in 2,2-disubstituierten 1,3-Dioxanen (1976)
    Springer
    Monatshefte für Chemie 107 (1976), S. 1-17 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Introduction of substituents in position 2 of 1,3-dioxanes decreases the torsional angles of the OCH2CH2CH2O moiety (∅4, 5, ∅5, 6) indicating an enhanced flattening in this part of the molecule. In geminally substituted 2-alkyl-2-phenyl-1,3-dioxanes the phenyl group isaxial, andgonal with respect to the rotameric state, while in ortho substituted derivatives, e.g. 2-methyl-2-(o-methylphenyl)-1,3-dioxane theaxial phenyl ligand assumes an intermediate rotameric position. Theaxial preference is not influenced by intramolecular dipole—dipole interaction generated by a p-substituent in the phenyl group as is shown for various 2-methyl-2-(p-substitutedphenyl)-1,3-dioxanes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00909077
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  • 2
    Electronic Resource
    Electronic Resource
    Darstellung, chiroptische eigenschaften und absolute Konfiguration von 4,14-disubstituierten [2.2]Metacyclophanen (1976)
    Springer
    Monatshefte für Chemie 107 (1976), S. 195-208 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Resolution of [2.2]metacyclophane-4,14-dicarboxylic acid (2) was achieved by crystallization of its (+)- and (−)-α-phenylethylamine salts. Chemical correlation with (−)-(S)p-[2.2]metacyclophane-4-caboxylic acid (−)-11 via its monobromo derivative (−)-8 established the absolute configuration of the dicarboxylic acid as (−)-(S)p-2. The key compound (−)-8 was prepared by partial lithiation and subsequent carboxylation of 4,14-dibromo[2.2]metacyclophane (1) and resolution with (−)-phenylethylamine. Recently proposed rules correlating the absolute configurations of planarchiral compounds with theirCD-spectra are discussed and a comparison of the chiroptical properties of 4,14-di- and 4-mono-substituted [2.2]metacyclophanes is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00909095
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  • 3
    Electronic Resource
    Electronic Resource
    Wannen- und Sesselformen des Benzolringes (1976)
    Springer
    Monatshefte für Chemie 107 (1976), S. 565-579 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A comparison of structural data of bent aromatic molecules demonstrates the existence of two discernible boat forms of the benzene ring, which can be described formally in terms of 1–4 or 2–6/3–5 foldings, resp. While in 3-[1,3],6°-[1,3,4,6],9°-[1,3]tribenzaspiro[5.5]undecaphane (triple layered [2.2]metacyclophane) (7) the peripheral benzene rings adopt a boat conformation, the shape of the central ring is chairlike. This was concluded by NMR-spectroscopical methods from the constancy of the torsional angles of the bridges compared with the isomer6 together with structural considerations. Therefore the isomer ratio6∶7 should reflect to a significant extent the relative stabilities of boat and chair shaped benzene rings. By means of these conclusions a stability sequence for the isomers of multi layered [2.2]metacyclophanes can be deduced. In connection with this study a synthesis of triple layered [2.2]metacyclophanes is offered, which opens the door to substituted derivatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00906887
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  • 4
    Electronic Resource
    Electronic Resource
    Concerning the applicability of a chirality function to different chirality observables (1979)
    Springer
    Monatshefte für Chemie 110 (1979), S. 1003-1009 
    Details
    ISSN: 1434-4475
    Keywords: Circulardichroism ; Chirality function ; 2,2′-Spirobiindanes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Anwendbarkeit einer Chiralitätsfunktion zur Beschreibung einer bestimmten chiroptischen Eigenschaft einer Molekülklasse impliziert keineswegs auch deren Gültigkeit für andere Chiralitätsbeobachtungen. Ungeachtet der Tatsache, daß Molrotationen ([M]λ) aus Einzelbeiträgen elektronischer Übergänge zusammengesetzt sind, kann es vorkommen, daß eine Chiralitätsfunktion, die den optischen Drehwerten einer Molekülklasse genügt, für den Circulardichroismus (CD) ungeeignet ist. Dies läßt sich anhand von [M] und CD-Daten optisch aktiver 5,5′-disubstituierter 2,2′-Spirobiindane zeigen.
    Notes: Abstract The applicability of a chirality function for the description of a special chiroptical property of a class of compounds does not imply its sufficiency for other observables of optical activity. Notwithstanding the fact, that molar rotations ([M]λ) can be understood in terms of contributions from electronic transitions, a chirality function consistent with the optical rotations of a kind of molecules may turn out inadequate for the circular dichroism (ed). This is demonstrated by means of [M] and ed data of optically active 5,5′-disubstituted 2,2′-spirobiindanes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00906695
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  • 5
    Electronic Resource
    Electronic Resource
    Restricted helix inversion in chiral 2,18-bridged biliverdins (1989)
    Springer
    Monatshefte für Chemie 120 (1989), S. 789-795 
    Details
    ISSN: 1434-4475
    Keywords: Helix inversion ; Bridged biliverdins ; Interconversion barrier ; Circular dichroism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Energiebarriere für die Helixinversion von Biliverdinen läßt sich durch Überbrücken der Pyrrolinonringe mit einer C-4 Einheit auf das Doppelte erhöhen. Derartige Verhältnisse liegen in den chiralen Diastereomeren des 2,18-(1′,4′-Dimethoxybutan-1′,4′-diyl)-8,12-bis(2″-methoxycarbonylethyl)-3,7,13,17-tetramethyl-1,19-(21H,24H)-bilindions1 und seines Hydroxyabkömmlings2 vor. Die dadurch bedingten Torsionsrestriktionen im Bilatrienteil stellen die Grundlage für eine Spaltung durch asymmetrische Umwandlung erster Art mit optisch aktiver Mandelsäure dar. Die Barrieren liegen zwischen 85 und 90 kJ mol−1 (293 K) und wurden aus der Geschwindigkeit der Isomerisierungsprozesse (M-RR)-1 b⇌(P-RR)-1 a, (P-SS)-1 b⇌(M-SS)-1 a, sowie des Razemisierungsprozesses (P-RS)-1 c⇌(M-RS)-1 c mittels Circulardichroismus bestimmt. Ähnliche Ergebnisse wurden für die Isomeren von2 erhalten.
    Notes: Summary The energy barrier to helix inversion in biliverdin is doubled if the pyrrolinone rings are bonded by a four-link chain as present in the chiral diastereoisomers of 2,18-(1′,4′-dimethoxybutane-1′,4′-diyl)-8,12-bis(2″-methoxycarbonylethyl)-3,7,13,17-tetramethyl-1,19-(21H,24H)-bilindion1 and its hydroxy derivative2. The torsional restrictions thus imposed on the bilatriene moiety provide the basis for resolution by first-order asymmetric transformation with optically active mandelic acid. Interconversion barriers at 293 K range from 85 to 90 kJ mol−1 and were determined monitoring the rate of isomerization processes (M-RR)-1 b⇌(P-RR)-1 a, (P-SS)-1 b⇌(M-SS)-1 a, and the racemization process (P-RS)-1 c⇌(M-RS)-1 c by c.d. spectroscopy. Similar results were obtained with the bridged biliverdins2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00809973
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  • 6
    Electronic Resource
    Electronic Resource
    Gezielte Konformationsänderungen an cyclischen Systemen, 2. Mitt.: Konformere 2-Phenyl-1,3-dithiane (1975)
    Springer
    Monatshefte für Chemie 106 (1975), S. 175-185 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In 2-phenyl-1.3-dithiane (1) and its p-methyl derivative (2) theequatorial phenyl adopts a conformation coinciding with the symmetry plane of the molecule. For 2-(2′-methylphenyl)-1.3-dithiane (4) acisoid relation of theaxial hydrogen on C-2 and the aromatic methyl group was established. This conformation can be changed by substitution of position 2 by methyl: in this geminally substituted compound (3), phenyl no longer assumes theequatorial position, and the plane of the phenyl group isperpendicular to the symmetry plane of the molecule. These deductions depend on the deshielding effect of sulphur and the diamagnetic anisotropy of the aromatic ring in the NMR spectra influencing the chemical shifts of the orthoprotons and of the protons of the dithiane ring respectively. The influence of the conformation on both of these effects is taken into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00914511
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  • 7
    Electronic Resource
    Electronic Resource
    Zur Theorie der Chiralitätsfunktionen (1978)
    Springer
    Theoretical chemistry accounts 49 (1978), S. 93-100 
    Details
    ISSN: 1432-2234
    Keywords: Theory of chirality functions ; First and second approximation procedure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The Algebraic Theory of Chirality Functions is derived by means of exclusively qualitative considerations. Hence, the significance of quantitative results is questionable. Moreover the construction of “Näherungsansätze” (”Approximation-Ansatz”), which may be interpreted as semiempirical methods, is achieved on the basis of plausibility and mathematical simplicity. Since physical arguments are not included, the consistency or inconsistency of “Näherungsansätze” with experimental results do not justify direct physical conclusions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00553787
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  • 8
    Electronic Resource
    Electronic Resource
    Zur Theorie der Chiralitätsfunktionen (1978)
    Springer
    Theoretical chemistry accounts 49 (1978), S. 93-100 
    Details
    ISSN: 1432-2234
    Keywords: Theory of chirality functions ; First and second approximation procedure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The Algebraic Theory of Chirality Functions is derived by means of exclusively qualitative considerations. Hence, the significance of quantitative results is questionable. Moreover the construction of “Näherungsansätze” (”Approximation-Ansatz”), which may be interpreted as semiempirical methods, is achieved on the basis of plausibility and mathematical simplicity. Since physical arguments are not included, the consistency or inconsistency of “Näherungsansätze” with experimental results do not justify direct physical conclusions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02399056
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  • 9
    Electronic Resource
    Electronic Resource
    Conformation control of bilatrienes by peptides: A survey (1991)
    Springer
    Monatshefte für Chemie 122 (1991), S. 89-100 
    Details
    ISSN: 1434-4475
    Keywords: Bilipeptides ; Conformation control ; Chiral discrimination ; Bilatrienes, non-helical
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Eine gezielte Auswahl von Bilipeptiden wurde dargestellt; ihre UV-VIS und CD-Spektren wurden bezüglich einer konformativen Einflußnahme auf die kovalent gebundenen Tetrapyrrol-Einheiten untersucht und die Ergebnise durch kürzlich veröffentlichte ergänzt. Aus den so zugänglichen umfangreichen Daten lassen sich einige Charakteristika in der Bauweise der Peptidketten herleiten, die die Wechselwirkung mit dem Bilatrienteil bestimmen. Es zeigt sich, daß der Ligand zumindest drei Amidbindungen aufweisen muß, um ausgeprägte Konformationsänderungen hervorzurufen. Diese Einflußnahme äußert sich entweder in einem vollständigen Übergang vonM inP helikale Bilatrien-Spezies und kommt durch gleichzeitige Inversion aller Torsionswinkel zustande, oder aber sie bewirkt eine Streckung des Bilatrienteils. Die Art der Konformationsänderung läßt sich durch Variation der Position einer Prolyleinheit innerhalb eines vorgegebenen Peptides lenken.
    Notes: Summary A variety of bilipeptides has been synthesized and investigated by UV-VIS and CD spectroscopy to explore the conformational influence of peptide ligands on the covalently bound tetrapyrrol moiety. The results obtained are complemented by those reported previously. From the comprehensive data thus available several features of the peptidic chain regulating interactions with the bilatriene moiety have been elucidated. Accordingly, the presence of three amide linkages at the ligand is prerequiste for induction of pronounced conformational changes consisting either in a complete transition ofM intoP helical bilatriene species by inversion of all torsional angles, or in a stretching of the chromophore. The kind of conformational influence can be controlled by varying the position of the prolyl entity within a given peptide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00815170
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  • 10
    Electronic Resource
    Electronic Resource
    Zur Anwendbarkeit von Ringstrommodellen in der Konformationsanalyse (1977)
    Springer
    Monatshefte für Chemie 108 (1977), S. 1371-1378 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The classical (Johnson-Bovey) and quantum mechanical (Haigh-Mallion) approach accounting for the shielding contribution to protons in the proximity of aromatic nuclei are compared with respect to their applicability in conformational analysis. This is accomplished by means of the1H-NMR spectra of various cyclophanes their geometries being fairly well known from X-ray data or other independent methods. The chemical shifts of the monitor protons (all of them being situated above or below the plane of the benzene ring considered) are consistent with shielding effects predicted by the classical theory notwithstanding the fact that the benzene hexagons are not strictly planar in any of these systems. In contrast, the quantum mechanical treatment considerably underestimates the shielding of protons in those regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01046451
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