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Vibrational spectra, co-operative intramolecular hydrogen bonding and conformations of calix[4]arene and thiacalix[4]arene molecules and their para-tert-butyl derivatives
Authors
Antipin I.
Chernova A.
+8 more
Katsyuba S.
Konovalov A.
Kovalenko V.
Shagidullin R.
Solovieva S.
Stoikov I.
Vandyukova E.
Zverev V.
Publication date
1 January 2005
Publisher
Abstract
The IR and Raman spectra and conformations of calix[4]arene, thiacalix[4]arene and their p-rerf-butyl derivatives have been analysed within the framework of scaled quantum mechanics (SQM). It is shown that the introduction of four p-tert-Bu groups into the calixarene molecules influences the relative energies of their conformers and the enthalpy of the cooperative intramolecular H-bonding (ΔHintra) almost negligibly. ΔHintra, evaluated from Iogansen's rule, amounts to ∼ 26-28 kcal mol-1 for the calixarenes and ∼20-21 kcal mol -1 for the thiacalixarenes, which essentially exceeds the enthalpies of non-cooperative H-bonds formed by related phenols. As a result of this strong bonding, bands of stretching, bending and torsion vibrations of an eight-membered cyclic system (OH ⋯)4 arise, e.g., two δ(OH)4 bands are observed in the IR spectra of the most highly symmetric C4 cone conformations of calix[4]arene and thiacalix[4]arene. The "duplication" of the number of OH infrared bands is a good new indicator of cooperativity of intramolecular H-bonding of the calixarenes. © The Royal Society of Chemistry 2005
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Last time updated on 07/05/2019