Cyclic Hydrogen-Bonded System with Large Proton Polarizability in CalixarenesAn FT-IR Study

Abstract

In calixarenes hydrogen-bonded rings are present. One proton was removed from the four-and six-membered rings, respectively, by such strong bases as 1,3,4,6,7,8-hexahydro-1-methyl-2H-pyrimido[1,2-a]pyrimidine (MTBD) and phosphazene (P 2 Et), respectively. In the FT-IR spectra of acetonitrile solutions in which these deprotonated molecules are present, intense continua are observed, demonstrating that these negatively charged rings show large proton polarizability due to collective proton fluctuation. These proton polarizabilities increase with increasing size of the rings. This latter result is in good agreement with our earlier theoretical treatments.

GIAO-DFT calculated and experimentally derived complexation-induced chemical shifts of calix[4]arene–solvent inclusion complexesElectronic supplementary information (ESI) available: calculated and observed NMR data and geometrical details for complexes 1–3, 1–4 and 1–5. See http://www.rsc.org/suppdata/p2/b1/b110078p/

“…However, this methodology strongly depends on the accessibility of single-crystalline material. In cases where such crystalline material is not available, 13 C CP-MAS NMR, 7-16 vibrational spectroscopy, [17][18][19][20][21][22][23][24] or thermochemical methods 25-28 are applicable. In solution, NMR titration experiments have found widespread use for the characterisation of inclusion processes.…”

The influence of protonation on molecular structure and physico-chemical properties of gossypol Schiff bases

“…The presence of these bands is related to the C-H stretching vibrations of the C-H bonds in the trans-arrangement to the lone electron pair at the N atom. [38][39][40][41] The Bohlmann bands of the propyl-morpholine moieties in the spectrum of S2 are found at 2818 cm -1 and 2779 cm -1 (Fig. 3b).…”

A vibrational spectroscopic study of clathrates of resorcarene‐based cavitands

“…Theoretically, one should expect a band splitting into four components in accordance with the different orientations of the four toluene molecules in the crystal lattice. This can only be observed for the strongest IR bands of toluene (bands 4 , 11 and 16a ; see Supporting information). Furthermore, the relative intensities of the components should be similar.…”

“…In the beginning of the calixarene-related chemistry, Fourier transform infrared (FTIR) spectroscopy was important to unravel the cyclic hydrogen bonding system at the lower rim fixing the cone conformation of these compounds. 1 Examples for the use of vibrational spectroscopy as an efficient tool to characterize host-guest complexes of calixarenes and resorcarene-based cavitands in the solid state and in solution are still scarce, [4][5][6][7][8][9] and still mainly limited to the investigation of hydrogen-bonded, [10][11][12][13] or surface-bound systems. 14,15 Acid-induced cyclocondensation of 2-methylresorcinol with para-substituted benzaldehydes gives rise to the corresponding chair methylresorc [4]arenes 1a, b in fair to excellent yields.…”