13C nuclear magnetic resonance study of the protonation of 2,2,4-trimethyl-1,5,9-triazacyclododecane

13 C N.m.r. spectroscopy has been used to investigate the protonation of 2,2,4-trimethyl-1,5,9-triazacyclododecane. The chemical shifts which occur upon protonation are interpreted as indicating that each protonation step results in the protonation of only one nitrogen atom, and that the sequence is probably N-5, N-9, and then N-1. There is some evidence indicating that a hydrogen bond is formed between N-1 and N-9 during the second protonation step. Chemical shifts observed are due to protonation of the nitrogen atom and to conformational changes within the molecule. The significance of these results for the determination of the protonation sequence of aliphatic polyamines is discussed.