Spectroscopic studies of N-methylpiperidine betaine complexes with phenols

Ten 1:1 crystalline complexes of N-methylpiperidine betaine with phenols (pKa from 9.55 to 0.33) were synthesised and analysed by UV– vis, 1H and 13C NMR and FTIR spectroscopies. The UV–vis spectra of complexes of moderately strong phenols show separate bands for A– H· · ·B and A2· · ·HBþ species. Sigmoidal plots of proton and carbon chemical shifts of the NþCH2 group versus pKa values of phenols and changes of absorption in FTIR spectra in the 3200–1800 and 1500–400 cm21 regions additionally confirmed the A–H· · ·B O A2· · ·H–Bþ equilibrium in the complexes investigated. q 2004 Elsevier B.V. All rights reserved.