Protonation of Tetrapropoxy-4-tert-butylcalix[4]arene: NMR Study of Interaction and Probable Structures of the Product
Using 1 H and 13 C NMR spectroscopy, the interaction of tetrapropoxy-p-tert-butyl-calix[4]arene (1) with H 3 O + ions produced by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and traces of water was studied in nitrobenzene-d 5 . It was shown that 1 readily forms an equimolecular complex with H 3 O...
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Published in | Supramolecular chemistry Vol. 20; no. 5; pp. 487 - 494 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
Taylor & Francis Group
01.07.2008
Taylor & Francis: STM, Behavioural Science and Public Health Titles |
Subjects | |
Online Access | Get full text |
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Summary: | Using
1
H and
13
C NMR spectroscopy, the interaction of tetrapropoxy-p-tert-butyl-calix[4]arene (1) with H
3
O
+
ions produced by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and traces of water was studied in nitrobenzene-d
5
. It was shown that 1 readily forms an equimolecular complex with H
3
O
+
. The equilibrium constant K of its formation is 2.6 at 296 K. Exchange between bound and free 1 is fast even under mild excess of HDCC, the correlation time τ
ex
being about 0.13 ms. NMR shows that H
3
O
+
is bound to the aryl-oxygen atoms and this binding forces the calixarene cup to adopt a more open and symmetrical conformation. This conclusion is in full accord with high precision quantum DFT calculations which find one structure of the complex corresponding to a global energy minimum, in which the H
3
O
+
ion is bound to three of the oxygen atoms by strong hydrogen bonds and to the remaining oxygen by two weaker hydrogen bonds. The calixarene part is forced into a C
4
symmetrical opened form.
When stored for weeks, the complex gradually transforms into other forms, most probably its hydrates, according to spectral evidence and DFT calculations. |
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ISSN: | 1061-0278 1029-0478 |
DOI: | 10.1080/10610270701422065 |