Protonation sequence of linear aliphatic polyamines by 13C NMR spectroscopy

The13C NMR spectra are reported as a function of pH for 4,7-diazadecane-1,10-diamine, 4,8-diazaundecane-1,11-diamine and 3,6,9-triazaundecane-1,11 -diamine. The previously reported amine shift parameters π and π+ are used to determine the protonation sites in the partially protonated intermediate forms of these and a further five polyamines whose 13C–pH profiles have been published. The use of this simple method for determining protonation sequences is examined critically.