Abstract: In this article, based on the traditional theory of mass spectra, the inductive effect index of substitutes of both styles nitrogen atoms(N_a and N_b) in indole alkaloids are calculated, respectively, utilizing the formula proposed by Jiang Ming-qian. And then, the charge sites in ionization source and mass spectral cha-racteristic are predicted by comparing the inductive effect index of N_a with that of N_b in same molecule. The results show that all predictive mass spectral characteristic(base peak) are correct. So the conclusion is gained that the charges localize on the nitrogen atom with lower inductive effect index. In addition, a facile approach to predict the mass spectral characteristic of the corresponding compounds is proposed based on the above conclusion.

Key words: Inductive effect index, Mass spectra, Indole alkaloids, Prediction of mass spectral characteristics