The conformational behaviour of thiacalix[4]arenes: the pinched cone–pinched cone transition

Abstract

This work is focused on the dynamics and thermodynamics of the pinched cone ↔ pinched cone interconversion of calix[4]arenes. The behaviour of methylene bridged non-substituted tetraalkoxycalix[4]arene and its tetraalkoxythiacalix[4]arene analogue is compared. Energetic and structural changes during this interconversion have been closely studied by HF and DFT quantum chemistry methods in combination with temperature -dependent 1 H NMR spectroscopy. The most important stationary points-minima and transition states-on the potential energy surface have been identified and their symmetry and other structural properties have been determined.

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

“…2), which has previously been found for similar structures. 21 The low temperature NMR experiments completely confirmed this hypothesis. With a temperature decrease compound 7 exhibits the strong broadening and then splitting of the signals (Fig.…”

“…For instance, for the tetra O propyl calix [4]arene derivative under the comparable con ditions, ΔG ≠ 303 is lower than 9.8 kcal mol -1 . 21 The higher activation energies of the interconversion for the larger macrocyclic ring of the thiacalix [4]arene derivatives com pared to the activation energies of the calix [4]arenes are possibly caused by the stabilization of the С 2v forms in the case of the thiacalixarenes due to the conjugation of the bridging sulfur atoms with the aromatic rings. The higher stability of the pinched cone conformation in the case of the unsubstituted at the upper rim thiacalix [4]arenes is indirectly specified by the fact that starting thiacalix [4]arene 2 in the crystalline state also has the С 2v symmetry according to the IR spectroscopic 31,32 and X ray diffraction 8 data.…”

Experimental Evidence for Unusual Protonation of Tetraethyl p-tert-Butylcalix[4]arene Tetraacetate and the Most Probable Structure of the Resulting Complex

“…The average spectral shape is caused by an interconversion between two identical structures (pinched cone) which is fast on the NMR time scale at normal temperature [19]. This spectral behavior is quite analogous to that of the dimethylthioamide derivative of the same calixarene.…”

“…NMR spectra [18,19]. The average spectral shape is caused by an interconversion between two identical structures (pinched cone) which is fast on the NMR time scale at normal temperature [19].…”

Direct C–H azidation of calix[4]arene as a novel method to access meta substituted derivatives

“…3) which is well known in calix[4]arene chemistry. 1,13 This process can be clearly illustrated in the 1 H NMR temperature-dependent spectra of bis-triazole 5a (Fig. 2).…”