Conformational isomerism and self-association of calixarene building blocks in non-polar solution studied by Fourier transform infrared spectrometry

Bert T.G. Lutz, Gonzalo Astarloa, John H. van der Maas, R.G. Janssen, Rob G. Janssen, Willem Verboom, David Reinhoudt

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Abstract

In order to establish the conformational equilibrium of calix[6]arene derivatives, a series of phenolic building blocks differing in chain length (oligomers) have been studied in solution by Fourier transform infrared spectrometry (FT-IR). Different intramolecular OH ¿ X interactions have been established in the calixarene building blocks, i.e. OH ¿ ¿, OH ¿ OH, OH ¿ OCH3 and a bifurcated OH ¿ OH/OCH3 or OH ¿ OH/OH one. Concentration-dependent measurements show that the ¿biphenol¿ and ¿triphenol¿ oligomers form cyclic dimers even at very low concentration (<10¿5 M). The presence of a molecular conformation where the terminal hydroxyl groups form part of a linear (cooperative) H-bond seems to promote cyclic self-association. Comparing p-tert-butylcalix[4]arene with p-tert-butylcalix[6]arene reveals that fixation of the skeleton strengthens the circular H-bond. Intramolecular OH ¿ OCH3 or OH ¿ ¿ interaction prevents the formation of associates for the building blocks with only one terminal OH group at relatively high concentration (> 10¿2 M). Preliminary MM3 calculations were performed to support conformational assignment.
Original languageUndefined
Pages (from-to)29-40
Number of pages12
JournalVibrational spectroscopy
Volume10
Issue number10
DOIs
Publication statusPublished - 1995

Keywords

  • METIS-106644
  • IR-12399

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