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

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-2 H -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.