The imine protons of nitrogen-15 labeled ketimines exhibit temperature-dependent nuclear magnetic resonances. Analysis of the effect of concentration of substrate on the mean lifetime indicates that the spectral changes result from a bimolecular exchange of protons between imines. The activation energy of this process in diphenylketimine-^(15)N was determined to be 13.8 ± 2 kcal./mole, whereas in sec-butylphenylketimine-^(15)N the activation energy was about 6 kcal./mole. In the latter case, separate resonances were observed for the distinct syn and anti isomers.
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Lambert et al. (1965) studied this question.