Vibrational spectra, co-operative intramolecular hydrogen bonding and conformations of calix[4]arene and thiacalix[4]arene molecules and their para-tert-butyl derivatives

Abstract

The IR and Raman spectra and conformations of calix[4]arene, thiacalix[4]arene and their p-tert-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 (DeltaH(intra)) almost negligibly. DeltaH(intra), evaluated from Iogansen's rule, amounts to approximately 26-28 kcal mol(-1) for the calixarenes and approximately 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 delta(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.

Hydrogen Bond Energies and Cooperativity in Substituted Calix[n]arenes (n= 4, 5)

“…38 The interconnected network of hydrogen bonds leads to a phenomenon termed "cooperativity", 39,40 which can be gauged indirectly from the geometry, dipole moments, and IR spectral frequencies and band intensities. 40 45,46 A series of NMR relaxation measurements in nonpolar solvents were applied for studying the dynamics of the circular hydrogen bond array in CX [4]. 29 Subsequently, cooperative intramolecular hydrogen bonding in CX [4] and S-CX [4] and their t-Bu derivatives has further been investigated.…”

Intramolecular co-operative hydrogen bond in calix[n]arenes (n = 4, 6, 8) bearing bulky substituents

“…The band contour is virtually symmetrical, the observed low frequency narrow bands were assigned to the ν(СН) stretching vibrations of the macrocycle fragments, the stretching vibrations of the СН groups in aromatic rings having the highest frequencies among them. [17][18][19] Calixarene 6 is of particular interest, since, apart from the ОН groups at the lower rim of the molecule, it has six СООН groups at the upper one. In the IR spectrum of this derivative, the absorption bands in the region 3540 cm -1 , which are responsible for the non bonding hydroxy fragments of the carboxy groups, are absent.…”

Synthesis and complexation properties of carbonyl-containing thiacalix[4]arenes

“…8,31,32 These regularities are the same in the classical analogs of compounds 1 and 2. 31, 32 The aforesaid indicates that the steric arrangement of substituents at the lower rim of thiacalixarenes unsubsti tuted at the upper rim or bearing the tert butyl group at this rim should substantially be different; therefore, their complexation ability will also differ. This is indicated by the data on extraction of alkaline metal cations by tet raesters of the classical calix [4]arenes with both the sub stituted and free upper rim, 33 and the macrocycles bear ing the tert butyl groups at the upper rim exhibit the better extraction properties.…”