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Issue 6, 1997
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The first acid constant of calix[4]arenes


A series of calix[4]arenes containing a single p-nitrophenol unit (or two p-nitrophenol units) have been synthesized by fragment condensation. Their first acid constant (pKa1) has been determined in 2-methoxyethanol–water (9 : 1) by optical titration. Relative to the corresponding linear trimers with a p-nitrophenol in the middle, a decrease of pKa1 by 2.1 units or more is observed, which can be explained entirely by intramolecular hydrogen bonds stabilising the monoanion. In this way electron-withdrawing p-substituents in the opposite phenolic unit lead to a further decrease in pKa1, while a distortion of the cone conformation by m-methyl groups causes a slight increase. The structure of one calix[4]arene was further confirmed by single crystal X-ray analysis showing the molecule in the usual cone conformation.

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Article information

J. Chem. Soc., Perkin Trans. 2, 1997, 1193-1200
Article type

The first acid constant of calix[4]arenes

M. Backes, V. Böhmer, G. Ferguson, C. Grüttner, C. Schmidt, W. Vogt and K. Ziat, J. Chem. Soc., Perkin Trans. 2, 1997, 1193
DOI: 10.1039/A607259C

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