Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 24, Issue 17, Pages 4436-4444Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201705955
Keywords
calix[4]arenes; conformational analysis; kinetics; molecular switching; NMR spectroscopy
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Funding
- University of East Anglia
- University Claude Bernard Lyon 1
- CNRS
- Region Rhone-Alpes (Cluster de Recherche Chimie)
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Calix[4]arenes are unique macrocycles that through judicious functionalisation at the lower rim can be either fixed in one of four conformations or remain conformationally flexible. Introduction of propynyl or propenyl groups unexpectedly provides a new possibility; a unidirectional conformational switch, with the 1,3-alternate and 1,2-alternate conformers switching to the partial cone conformation, whilst the cone conformation is unchanged, under standard experimental conditions. Using (HNMR)-H-1 kinetic studies, rates of switching have been shown to be dependent on the starting conformation, upper-rim substituent, where reduction in bulk enables faster switching, solvent and temperature with 1,2-alternate conformations switching fastest. Ab initio calculations (DFT) confirmed the relative stabilities of the conformations and point towards the partial cone conformer being the most stable of the four. The potential impact on synthesis through the click reaction has been investigated and found not to be significant.
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