Search results for "Intramolecular force"
showing 10 items of 599 documents
Combination of single-molecule magnet behaviour and luminescence properties in a new series of lanthanide complexes with tris(pyrazolyl)borate and ol…
2020
A series of tris(pyrazolyl)borate mono-, di- and trinuclear complexes, [Tp2Ln]nX (Ln = Eu, Tb, Gd, Dy, Xn− = various mono-, bis- and tris(β-diketonates) has been prepared. The Tb3+ and Dy3+ complexes are luminescent single molecular magnets (SMM) and exhibit luminescence quantum efficiencies up to 73% for the Tb3+ and 4.4% for the Dy3+ compounds. Similar Eu3+ complexes display bright emission only at lower temperatures. The Dy3+ and Tb3+ complexes possess SMM behavior in a non-zero dc field at low temperatures, while the polynuclear Dy3+ complexes also show slow magnetic relaxation even in zero dc field up to 8 K. Ueff-values determined from dynamic magnetic measurements were up to 31 and 6…
Darstellung einiger oligomerer Cyclo{oligo[(2-hydroxy-1,3-phenylen)methylen]}e. Spektroskopische Untersuchung ihrer Pseudorotation
1978
Es wird die Darstellung von Cyclo{tris[(2-hydroxy-5-methyl-1,3-phenylen)methylen]-(2-hydroxy-5-tert-butyl-1,3-phenylen)methylen} (4a), Cyclo{bis[(2-hydroxy-5-methyl-1,3-phenylen)methylen]-bis[(2-hydroxy-5-tert-butyl-1,3-phenylen)methylen]}(4b) und Cyclo-{pentakis[(2-hydroxy-5-methyl-1,3-phenylen)methylen]} (4c) beschrieben. Die IR-Spektren zeigen, das die phenolischen Hydroxygruppen der Vierringverbindungen 4a und 4b intramolekulare, vom Losungs(CCl4)- oder Zerteilungsmittel (KBr) weitgehend unabhangige Wasserstoffbrucken bilden, die bei der pentameren Ringverbindung 4c schwacher sind. Anhand der 1H-NMR-Spektren last sich bei diesen Verbindungen eine Pseudorotation nachweisen. Die Massenspe…
An Efficient Synthesis of Rubin’s Aldehyde and its Precursor 1,3,5-Tribromo-2,4,6-tris(dichloromethyl)benzene
2011
2,4,6-Tribromobenzene-1,3,5-tricarboxaldehyde (4) can be efficiently prepared in two reaction steps from 1,3,5-tribromobenzene. The intermediate 1,3,5-tribromo-2,4,6-tris(dichloromethyl)benzene (3) crystallizes from petroleum ether in its C3h structure. However, in CDCl3 solution it exists at room temperature in two isomeric forms: 3a (C3h) and 3b (Cs) (1:1.15).The intramolecular Br・・・Cldistances are much smaller than the sum of the van der Waals radii. Therefore, the exocyclic C-C bonds show a hindered rotation.
Bis-, Tris-, and Tetrakis(squaraines) Linked by Stilbenoid Scaffolds
2001
The oligosquaraines 1−5, with stilbenoid scaffolds, were prepared by multistep syntheses in which the final steps consisted of condensation reactions between the semisquaric acid 21 and multiple resorcinols 12b−15b and 17b. The target compounds exhibit intense (ϵ > 250000 L·mol−1·cm−1) and sharp absorption bands with maxima between 687 to 778 nm, depending on the conjugation in the stilbenoid scaffold. Comparison with the monosquaraine 6 as a model compound reveals intramolecular interactions between different donor−acceptor−donor moieties, which give rise to increased absorption intensities.
ChemInform Abstract: Bis-, Tris-, and Tetrakis(squaraines) Linked by Stilbenoid Scaffolds.
2010
The oligosquaraines 1−5, with stilbenoid scaffolds, were prepared by multistep syntheses in which the final steps consisted of condensation reactions between the semisquaric acid 21 and multiple resorcinols 12b−15b and 17b. The target compounds exhibit intense (ϵ > 250000 L·mol−1·cm−1) and sharp absorption bands with maxima between 687 to 778 nm, depending on the conjugation in the stilbenoid scaffold. Comparison with the monosquaraine 6 as a model compound reveals intramolecular interactions between different donor−acceptor−donor moieties, which give rise to increased absorption intensities.
Double asymmetric intramolecular aza-Michael reaction: a convenient strategy for the synthesis of quinolizidine alkaloids.
2021
A new methodology to access the quinolizidine skeleton in an asymmetric fashion was devised. It involves two consecutive intramolecular aza-Michael reactions of sulfinyl amines bearing a bis-enone moiety, in turn generated by a monodirectional cross metathesis reaction. The sequence, which takes place with excellent yields and diastereocontrol, was applied to the total synthesis of alkaloids lasubine I and myrtine.
Die Dissoziationskonstanten von 2,2?-Dihydroxydiphenylmethanderivaten
1973
The pK-values of the first and second degree of dissociation of 2.2′-dihydroxy-5-methyl-3′.5′-dinitro-diphenylmethane, 2.2′-dihydroxy-5-methyl-5′-nitro-diphenylmethane and 2.2′-dihydroxy-5.5′-dimethyl-3′-nitro-diphenylmethane were determined in aqueous solution at 25°C spectrophotometrically. Comparing the observed pK-values with those of 2-methyl-4.6-dinitrophenol, 2-methyl-4-nitrophenol, 2.4-dimethyl-6-nitro-phenol and 2.4-dimethylphenol, we found a decrease of the values of pK1 and an increase of pK2. We explain this by the formation of an intramolecular hydrogen bridge which stabilizes the anion of the half dissociated form. This assumption is supported by the UV spectra.
Mixed‐valence trinuclear manganese clusters : Influence of the electronic transfer on the magnetic properties
1990
The magnetic behavior of mixed‐valence trinuclear clusters d4‐d4‐d5 is discussed on the basis of a model which takes into account valence delocalization and Heisenberg exchange. This model considers the competing effect between the electronic transfer and the localization of the extra electron due to an asymmetry of the triangular entity. The magnetic properties of the mixed‐valence oxo‐centered Mn(II)‐Mn(III)‐Mn(III) complexes formulated as Mn3O(O2CR)6L3 (R=Me, L=pyridine) are discussed on the basis of the developed model, supporting a significant intramolecular electron transfer. A comparison of these results to those previously reported by assuming a valence‐trapped model is given. Carlo…
New alkoxo-bridged mixed-valence cobalt clusters: Synthesis, crystal structures and magnetic properties
2008
Two new Co II /Co III complexes, [{Co II Co III (mea) 3 } 2 (bpe) 3 ](ClO 4 ) 4 · 1.5CH 3 OH · 1.5H 2 O ( 1 ) and [ Co 4 II Co 3 III ( dea ) 6 ( CH 3 COO ) 3 ] ( ClO 4 ) 0.75 ( CH 3 COO ) 1.25 · 0.5 H 2 O ( 2 ) [Hmea = monoethanolamine H 2 dea = diethanolamine and bpe = 1,2-bis(4-pyridyl)ethane], have been obtained by reacting cobalt(II) perchlorate ( 1 and 2 ), Hmea ( 1 )/H 2 dea ( 2 ), bpe ( 1 ) and sodium acetate ( 2 ). The crystal structures of 1 and 2 have been solved by single crystal X-ray diffraction. Crystal 1 contains “Chinese lantern”-like shaped cations, resulting by connecting two {Co II Co III (mea) 3 } moieties with three flexible bpe ligands. The coordination sphere of the …
Solvent-Enhanced Diastereo- and Regioselectivity in the PdII-Catalyzed Synthesis of Six- and Eight-Membered Heterocycles viacis-Aminopalladation
2009
The Pd(II)-catalyzed intramolecular oxidative cyclization of tosyl-protected cis- and trans-N-allyl-2-aminocyclohexanecarboxamides was examined, and efficient syntheses of cyclohexane-fused pyrimidin-4-ones and 1,5-diazocin-6-ones were developed. In the course of the research, a marked solvent effect was observed on both the regio- and diastereoselectivity. Additionally, a novel Pd(II)-mediated domino oxidation, oxidative amination reaction was discovered. Our experimental and theoretical findings suggest that the reactions proceed via a cis-aminopalladation mechanism.