Search results for "conformation"
showing 10 items of 1414 documents
9‐Oxabicyclo[6.1.0]nonine
1989
Semiempirische quantenmechanische Rechnungen (MNDO) und Kraftfeldrechnungen (MM2) zeigen, das fur die drei konstitutionsisomeren cis-9-Oxabicyclo[6.1.0]nonine 1–3 jeweils zwei energiearme, zueinander diastereomere Konformere a und b existieren. Der synthetische Zugang zu den hoch gespannten Verbindungen 1–3 gelingt mit der Selenadiazolmethode oder durch Dehydrobromierung (Schemata 3, 4 und 6). Die NMR-spektroskopische Konformationsanalyse bestatigt bei 2 das vorhergesagte Konformerengleichgewicht; bei 1 gehen selbst bei –60°C die beiden Konformeren durch Umklappen des Achtrings schnell ineinander uber, und bei 3 ist praktisch nur eine Konformation populiert. 9-Oxabicyclo[6.1.0]nonynes Semie…
Bis(dichlorosilyl)methylamine - Synthesis, Crystal Structure, and Conformational Analysis in the Gas Phase
1999
A straightforward preparation has been found for bis(dichlorosilyl)methylamine, (SiHCl2)2NMe (1), involving reaction between H2NMe and an excess of SiHCl3, dissolved either in pentane or THF at 253 K. 1 and a side-product, 1,3,5-trichloro-2,4,6-trimethylcyclotrisilazane, (–SiHCl–NMe–)3 (2), were identified by elemental analysis, mass spectrometry and 1H-NMR-spectroscopy. Some physical, NMR- and IR spectroscopical properties of 1 were determined. The molecular and crystal structure of 1 was investigated by single crystal X-ray diffraction. Selected structural parameters: r(Si–N) 169.7(5), r(Si–Cl) 203.1(2)–204.4(2), r(C–N) 150.0(8) pm; a(SiNSi) 123.6(3), a(SiNC) 118.3(4)/118.0(4)°. Ab initio…
First Crystallographic Investigation of Complexes of cis-VO2+, cis-MoO22+, and trans-UO22+ Species with Schiff-Base Molecules Derived from 4,6-O-Ethy…
2001
The interaction of Schiff-base ligands derived from 4,6-O-ethylidene-β-D-glucopyranosylamine with cis-VO 2 + , cis-MoO 2 2+ , and trans-UO 2 2+ species have been studied by isolating and characterizing the corresponding products. The structures of one complex of each type of species have been established by single-crystal X-ray diffraction analysis. In all the complexes, the saccharide moiety adopts a chair conformation and has a β-anomeric form. A gradual increase in coordination number (5, 6, and 7) and a gradual variation in the geometry (distorted trigonal-bipyramidal, distorted octahedral, and pentagonal-bipyramidal) are observed on going from the complexes of cis-VO 2 + (mononuclear) …
First Annelated Azaphosphole-Ferrocenes: Synthetic Pathways and Structures
2012
The first annelated bis- and mono-3H-1,3-azaphosphole ferrocene sandwich compounds have been synthesized from aminoferrocenes, and their X-ray structures are compared to those of their selenide-protected P═Se analogues, showing net discrepancies both in metallocene backbone conformation and in fused-ring planarity.
syn ‐[2.2](1,3)Cyclophane durch doppelte Photocyclodimerisierung
1988
Durch doppelte Cyclodimerisierung wird in einer Photolyse in Losung aus dem 1,3-disubstituierten Benzol 3 das syn[2.2](1,3)Cyclophan 4 erhalten. Eine kombinierte Belichtung Festkorper/Losung ergibt bei 5 das analoge System 6 mit Estergruppen. Beide Reaktionen erfolgen streng regiospezifisch durch Kopf-Kopf-Verknupfung und stereospezifisch bezuglich der syn-Geometrie im Cyclophan und der trans-Konfiguration der Vierringsubstituenten. Die einzige stereochemische Freiheit besteht in der Anordnung der Vierringe, wobei die Isomeren 4/6a,b,c, den drei moglichen Rotameren in 3 und 5 entsprechen. Wahrend das Gerust von 4 starr ist, zeigt 6 bei Raumtemp. eine langsame Inversion des zentralen 10-Ring…
The Role of C–H···H–B Interactions in Establishing Rotamer Configurations in Metallabis(dicarbollide) Systems
2010
The aim of this work is to explore the self-interaction capability of the anion [3,3′-Co(1,2-C2B9H11)2]– through Ccluster–H···H–B (Cc–H···H–B) dihydrogen bonds. A set of theoretical and empirical data aiming to establish the main rules that account for the binding mode between the negatively charged borane framework made by [3,3′-Co(1,2-C2B9H11)2]– and the [NMe4]+ ions have been compiled. The interaction between cation and anion is mainly electrostatic but the covalent contribution is also proven and quantified. The existing intermolecular H···H short contacts have been studied and are compared with available data from the Cambridge Structural Database. The results show that the electronic …
Conformational Analysis of beta-Lactam-Containing Ferrocene Peptides
2009
The homochiral 3-amino-1-(4-methoxyphenyl)-4-phenyl-beta-lactam (≡ Alm) was conjugated with Boc-Ala giving Ala-Alm (9) after Boc-deprotection (Boc = tert-butoxycarbonyl, Ala = alanine). Coupling of FcCOOH (1) and Boc-Fca (10) with “ dipeptide” 9 resulted in the formation of FcCO-Ala-Alm (12) and the trisamide Boc-Fca-Ala-Alm (13), respectively (Fc = ferrocenyl, Fca = 1’ -aminoferrocene-1-carboxylic acid). The reactions were accomplished by the HOBt/EDC procedure and the products were obtained in good yields (HOBt = 1-hydroxybenzotriazole, EDC = N-(3-dimethylaminopropyl)-N’ -ethylcarbodiimide hydrochloride). Symmetrically 1, 1’ -disubstituted “ tetrapeptide” Fn(CO-Ala-Alm)2 (14) was prepared…
Bicyclo[6.1.0]nonine
1988
MNDO-Rechnungen zeigen, das fur die drei konstitutionsisomeren cis-Bicyclo[6.1.0]nonine (1–3) jeweils zwei energiearme, zueinander diastereomere Konformere a und b existieren. Zur experimentellen Uberprufung werden die mit der Selenadiazol-Methode oder durch Dehydrobromierung hergestellten, hoch gespannten Bicyclen mit Hilfe von 1H- und 13C-NMR-Messungen auf die Population der Konformeren und auf deren wechselseitige Umwandlung durch Inversion der Achtringe untersucht. Bicyclo[6.1.0]nonine MNDO calculations reveal that two diastereomeric conformations a and b of low energy exist for each of the three isomeric cis-bicyclo[6.1.0]nonynes (1–3). For the experimental proof, the highly strained b…
Über Germanium‐haltige Heterocyclen, I. Darstellung und Charakterisierung der 8‐Ring‐Verbindungen 2,2‐Dichlor‐1,3,6,2‐trithiagermocan und 5,5‐Dichlor…
1975
Die Darstellung der Titelverbindungen 3 und 4 wird beschrieben. 1H-NMR-, IR-, Raman- und Massenspektren werden zusammen mit den entsprechenden Spektren der analogen Zinnverbindungen 1 und 2 diskutiert. In Losungen der 8-Ringe 1 - 4 besteht ein Gleichgewicht zwischen zwei chiralen Wanne-Sessel-Konformeren uber eine achirale Sessel-Sessel-Konformation. Fur 1 wird ferner eine Berry-Pseudoration am trigonal-bipyramidal koordinierten Sn-Atom angenommen. Versuche zur Darstellung von analogen Si-Verbindungen werden erwahnt. On Heterocyclic Systems Containing Germanium, I. Synthesis and Investigation of the Eighy-membered Rings 2,2-Dichloro-1,3,6,2-trithiagermocane and 5,5-Dichloro-1,4,6,5-oxadithi…
Acid Titrations of poly(dG-dC).poly(dG-dC) in Aqueous Solution and in a w/o Microemulsion
2005
The model polynucleotide poly(dG-dC).poly(dG-dC) (polyGC) was titrated with a strong acid (HCl) in aqueous unbuffered solutions and in the quaternary w/o microemulsion CTAB/n-pentanol/n-hexane/water. The titrations, performed at several concentrations of NaCl in the range 0.005 to 0.600 M, were followed by recording the modifications of the electronic absorption and of the CD spectra (210or = lambdaor =350 nm) upon addition of the acid. In solution, the polynucleotide undergoes two acid-induced transitions, neither of which corresponds to denaturation of the duplex to single coil. The first transition leads to the Hoogsteen type synG.C+ duplex, while the second leads to the C+.C duplex. The…