Search results for "PIP"
showing 10 items of 1156 documents
Complete in-plane elastic characterisation under tensile tests of angle-ply laminates composed of polymer-matrix layers
2002
In this paper we present a new strategy to completely characterise the in-plane elastic properties of a large range of angle-ply laminates using only unidirectional tests. We consider laminates having the same number of identical plies in the α and – α directions. This new method uses some preceding results found by Verchery for orthotropic laminates, namely the conditions of existence of a specific direction ω, in which the shear-extension coupling is null. The characterisation of the laminate is then made using the results of three tensile tests: two in the orthotropy axes, and the third one in the ω direction, in order to have always a pure one-dimensional state of stress. We show that …
Macrocyclic (1,3)- and (1,4)-benzena-(1,4)-piperazinacyclophanes
1995
New large, up to 45-membered macrocycles were synthesised from piperazine and m- and p-2,6-bis(bromomethyl)xylene under high dilution conditions. X-ray structures of compounds 3a, 4a, 5a, and 8b were determined. Surprisingly, none of the macrocycles prepared showed any inclusion properties towards small guest molecules. Instead, the compounds were found to self-organize during the packing process into larger structures due to the complementary of the molecular skeletons. In the crystalline state 3a forms nets, where the macrocycles are bound by HCH…N interactions to each other. 4a exits in a dimeric structure, which, in turn, further extends to a sheet structure. The positively charged phan…
Chiral synthetic pseudopeptidic derivatives as triplet excited state quenchers
2009
The behavior of 6 pseudopeptidic models, synthesized by connecting different protected amino acids (Trp, Tyr, Phe, and Lys) with various diamino spacers, as quenchers of the triplet excited state of tiaprofenic acid (and its methyl ester), has been investigated. A series of quenching constants have been determined, which depend on the nature of the quencher and on the stereochemistry of the excited drug. A significant degree of stereodifferentiation has been found for the peptidomimetic synthesized with Phe and Tyr linked by a piperazine bridge. The obtained results support the utility of laser flash photolysis (LFP) as a tool to investigate the interactions between photoexcited drugs and s…
On the Dichotomic Behavior of the Z-2,4-Dinitrophenylhydrazone of 5-Amino-3-benzoyl-1,2,4-oxadiazole with Acids in Toluene and in Dioxane/Water: Rea…
2004
The mononuclear rearrangement (MRH) of the Z-2,4-dinitrophenylhydrazone (4a) and of the Z-phenylhydrazone (4b) of 5-amino-3-benzoyl-1,2,4-oxadiazole into the relevant triazoles 5a and 5b in toluene has been quantitatively investigated in the presence of trichloroacetic acid (TCA) and of piperidine at 313.1 K. While the behavior in the presence of piperidine recalls the one previously evidenced for some Z-hydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole, the study of the reactivity in the presence of TCA has most interestingly evidenced a general-acid-catalyzed rearrangement for “both” 4a and 4b. Thus, 4a offers the first example of a solvent-dependent dichotomic behavior in MRH processes o…
Tri- and tetraurea piperazine cyclophanes: synthesis and complexation studies of preorganized and folded receptor molecules.
2010
A series of symmetrical tri- and tetrameric N-ethyl- and N-phenylurea-functionalized cyclophanes have been prepared in nearly quantitative yields (86-99 %) from the corresponding tri- and tetraamino-functionalized piperazine cyclophanes and ethyl or phenyl isocyanates. Their conformational and complexation properties have been studied by single-crystal X-ray diffraction, variable-temperature NMR spectroscopy, and ESI-MS analysis. The rigid 27-membered trimeric cyclophane skeleton assisted by a seam of intramolecular hydrogen bonds results in a preorganized ditopic recognition site with an all-syn conformation of the urea moieties that, complemented by a lipophilic cavity of the cyclophane, …
Synthesis of a tetradentate piperazine ligand and a structural study of its coordination compounds
1999
Abstract A tetradentate ligand N,N′-bis(2-pyridylmethyl)piperazine (L1) and seven structures of its transition metal coordination compounds are described. Most of the compounds are of the general formula [M(L1)(NO3)2], with M=Cu2+, Co2+, Mn2+and Cd2+. In addition, a dimeric copper(II) compound, [Cu2(L1)(Ac)4](H2O)3, and polymeric silver(I) compounds, [Ag(L1)]n(NO3)n(EtOH)n and [Ag(L1)]n(SO3CF3)n, were formed. The overall structure of L1 in the metal complexes A–G varies with the size and electronic properties of the metal ions. Mononuclear complex A is a five-coordinated, B is a six-coordinated, and C and D are eight-coordinated metal complexes. The dinuclear Cu complex, E, is four-coordina…
Arabinosylamine in Asymmetric Syntheses of Chiral Piperidine Alkaloids.
2004
The stereodifferentiating potential of arabinosyl aldimines was utilized in stereoselective syntheses of 2-substituted dehydropiperidinones and their further transformation to 2,6-cis-substituted piperidinones. The absolute configuration was proven by X-ray analysis and by the synthesis of the enantiomerically pure alkaloid (+)-dihydropinidine. The presented method offers the possibility to synthesize piperidine derivatives enantiomeric to those obtained by the application of the corresponding galactosylamine auxiliary.
C−C versus C−N Annulation Reactions of 2-Alkyl-2-oxazolines and 2-Alkyl-2-thiazolines: A Simple Synthesis of Novel 3-Aminoindene, Phthalimidine, Pyrr…
2001
The effect of various aromatic and aliphatic dielectrophiles on the lithium azaenolates of 2-alkyl-2-oxazolines and 2-alkyl-2-thiazolines has been examined. This effect varies greatly, depending on the nature of the dielectrophile used. 3-Aminoindene (3) and 3-alkylidenephthalimidine (4−5) derivatives were formed as a result of the reactions with dielectrophiles derived from ortho-substituted benzonitriles. Similarly, 2-alkylidenepyrrolidine (7) and 2-alkylidenepiperidine (8) derivatives were obtained in high yields from 2-alkyl-2-oxazolines or 2-alkyl-2-thiazolines and aliphatic dielectrophiles derived from ω-haloalkyldiphenylacetonitrile. C−C versus C−N annulation reactions are discussed.
ChemInform Abstract: C-C versus C-N Annulation Reactions of 2-Alkyl-2-oxazolines and 2-Alkyl-2-thiazolines: A Simple Synthesis of Novel 3-Aminoindene…
2010
The effect of various aromatic and aliphatic dielectrophiles on the lithium azaenolates of 2-alkyl-2-oxazolines and 2-alkyl-2-thiazolines has been examined. This effect varies greatly, depending on the nature of the dielectrophile used. 3-Aminoindene (3) and 3-alkylidenephthalimidine (4−5) derivatives were formed as a result of the reactions with dielectrophiles derived from ortho-substituted benzonitriles. Similarly, 2-alkylidenepyrrolidine (7) and 2-alkylidenepiperidine (8) derivatives were obtained in high yields from 2-alkyl-2-oxazolines or 2-alkyl-2-thiazolines and aliphatic dielectrophiles derived from ω-haloalkyldiphenylacetonitrile. C−C versus C−N annulation reactions are discussed.
Über die cyclopolymerisation einiger bis-(N-vinyl)-verbindungen
1966
Durch Umsetzung von Vinylisocyanat mitAthylenglykol, Butandiol-1,4, Hexandiol-1,6, Octandiol-1,8, Brenzcatechin, Resorcin, Hydrochinon, cis- und trans-Chinit sowie Piperazin wurden die entsprechenden Bis-(N-vinyl)-Verbindungen hergestellt. Diese Monomeren werden unter gleichen Bedingungen radikalisch polymerisiert. Der Gehalt an seitenstandigen N-Vinylgruppen ergibt sich aus der bei saurer Hydrolyse gebildeten Menge Acetaldehyd. Der auf 0% Umsatz berechnete Doppelbindungsgehalt und damit der Cyclisierungsgrad hangt von der Struktur der Monomeren ab. Die Ergebnisse stimmen uberein mit der Ringbildungstendenz bei niedermolekularen Verbindungen (z. B. Ansaverbindungen) und werden an Hand von M…