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Convenient regioselective functionalization at the upper-rim of p-tert-butylcalix[8]arene through a protection-deprotection procedure
No full textA viable method to obtain calix[8]arenes selectively functionalized at the upper rim of 1,5-aromatic rings is reported. The procedure relies on protected, readily accessible 1,5-xylylene-bridged derivatives, which are easily deprotected by hydrogenolysis. The method allowed the synthesis of the first examples of calix[8]arenes partially substituted with p-nitro, p-amino, quinone and hydroquinone functionalitie
Regioselective O-substitution of p-tert-butylcalix[7]arene
No full textThe first examples of selectively functionalized calix[7]arenes have been obtained by weak-base promoted O-alkylation or O-benzoylation of p-tert-butylcallx[7]arene. Mono-, 1,3- and 1,4-disubstituted calix[7]arenes have been obtained in workable yields, while the 1,2,4,6-tetrasubstitution was achieved with surprisingly high selectivity (50-88% yield) by using K2CO3 as base. A rationale for this finding is propose
Molecular assembly of distal p-H-calix[4]dihydroquinone units
No full textThe solid-state self-assembly properties of distal dimethoxy-p-H-calix[4]dihydroquinone, 3, are described. Three
different crystalline forms were obtained under different crystallization conditions. The cone conformation is maintained in all three crystalline forms, being favored by lower rim hydrogen bond formation. The first crystal, 3A, is constituted by mutual-inclusion calixarene trimers connected to each other by water molecules. The second and third ones (3B and 3C) are formed by alternate layers of crystallographically independent calixarene molecules
Regioselective intramolecular bridging of p-tert-butylcalix[7]arene
No full textThe first examples of singly bridged calix[7]arenes 2-4 have been obtained by base-promoted direct O-alkylation of p-tert-butylcalix[7]arene with a variety of bis-electrophiles including BrCH2Cl, oligoethylene glycol ditosylates, and 1,4-bis(bromomethyl)benzene. 1,2-Bridging was favored with 'short bite' spanning elements, while the 1,4-isomer predominated with the others (yields up to 72% in the presence Of Cs2CO3). Assignment of bridging pattern was mainly based on chemical shift of OH groups, in some cases confirmed by 2D NMR experiments. A hampered conformiational mobility, depending on the position and nature of the bridge, was observed for compounds 2-
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Interconnected water channels and isolated hydrophobic cavities in a calixarene-based, nanoporous supramolecular architecture
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