Positive Charge Distribution of Secondary Alkylamines and Its Correlation with the Bond-Scission Probability Appearing in Their Mass Spectra

概要

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With respect to the correlation between scission probabilities and positive charge distributions on the skeletal bonds of amines appearing in their mass spectra, further research is reported on four secondary amines (diethylamine, dipropylamine, dibutylamine and methylbutylamine). In each secondary alkylamine the fragment ions formed by the scission of α–CC bond are the most abundant experimentally, <I>i.e.</I>, the scission probability of α–CC bond is the largest in monoamines as well. Agreement between experiments and LCBO-MO calculations on four secondary alkylamines is found to be satisfactory as in the case of propylamine, using the same semi-empirical parameters as those of monoamines in the calculation. It is shown that from detailed calculations of diethylamine by CNDO method the scission of α–CC bond is also easy due to concentration of the positive charge at the bond, theoretically in accordance with the semi-empirical calculation. Change of mass spectra <I>vs.</I> ionizing voltage is explained on a generalized scheme, which combines two existing theories of fragmentation (QET and MOT).
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