Acidity of the N~+CH_2 Protons in N-Phenacyl-R-pyridinium Bromides

摘要

UV-Vis,FUR,~1H and ~(13)C NMR and MS spectra of 19 N-phenacyl-R-pyridinium bromides and their ylides were measured and analysed.In crystals the investigated salts appear as keto-tautomer,but in water solutions in a keto-enol tautomeric equilibrium.In most salts,the N~+CH_2 hydrogens,undergo fast hydrogen-deuterium exchange in neutral D_2O at room temperature,which confirms the presence of some amount of enolic tautomers in aqueous solutions.The intensity of the ylide bands in the 385-480 nm region is substituent and time dependent and reflects the rates of their formation and decomposition.The ylides with electron-withdrawing substituents form and decompose much faster than those with electron-donating ones.