Spectroscopic studies of N-methylpiperidine betaine complexes with phenols

Ten 1:1 crystalline complexes of N-methylpiperidine betaine with phenols (pK(a) from 9.55 to 0.33) were synthesised and analysed by UV-vis, H-1 and C-13 NMR and FTIR spectroscopies. The UV-vis spectra of complexes of moderately strong phenols show separate bands for A-H...B and A(-)...HB+ species. Sigmoidal plots of proton and carbon chemical shifts of the N+CH2 group versus pK(a) values of phenols and changes of absorption in FTIR spectra in the 3200-1800 and 1500-400 cm(-1) regions additionally confirmed the A-H...B reversible arrow A(-)...H-B+ equilibrium in the complexes investigated. (C) 2004 Elsevier B.V. All rights reserved.