PROTON POLARIZABILITY DUE TO COLLECTIVE PROTON MOTION IN INTRAMOLECULAR HYDROGEN-BONDED SYSTEMS IN MONOPERCHLORATES OF 2,6-BIS((DIETHYLAMINO)METHYL)-4-R-PHENOL DI-N-OXIDES AS A FUNCTION OF THE PKA OF THE PHENOLIC GROUP

2,6-Disubstituted Mannich base di-N-oxides (2,6-DNO) and their mono- and diperchlorates were studied in CH2Cl2 solutions by FTIR and NMR spectroscopy. These compounds were investigated as a function of the acidity of the phenolic OH group. In the case of 2,6-disubstituted Mannich base di-N-oxides, the protons transfer to a large extent into intramolecular structurally symmetrical NO+H⋯ON ⇌ NO⋯H+ON hydrogen bonds with large proton polarizability. Thus with the system with a weakly acidic phenolic group the proton fluctuates probably between the two NO and the phenolate group. In the case of the monopercxhlorates of 2,6-disubstituted Mannich base di-N-oxides, intramolecular NO+H⋯OH⋯ON ⇌ NO⋯HO⋯H+ON hydrogen-bonded systems are observed which show large proton polarizability due to collective proton motion. The proton polarizability increases with increasing acidity of the phenolic OH group. Only with the system with the most acidic phenolic OH group the proton limiting structures have changed to a structure NO+H⋯O-⋯H+ON with which the two minima of the proton potentials are shifted toward the NO groups. These two wells are, however, very broad and the hydrogen-bonded system shows still weak proton polarizability. The behavior of the systems studied is compared with the behavior of the respective 2,6-disubstituted Mannich base system (2,6-D). © 1990 American Chemical Society.