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Structural and substituent effects on [M] +. vs. [MH] + formation in fast atom bombardment mass spectra of simple organic compounds
Author(s) -
Nakata Hisao,
Tanaka Katsunori
Publication year - 1994
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210290604
Subject(s) - chemistry , substituent , ion , mass spectrum , ionization , hydrogen atom , spectral line , fast atom bombardment , molecule , atom (system on chip) , ionization energy , analytical chemistry (journal) , medicinal chemistry , organic chemistry , group (periodic table) , physics , astronomy , computer science , embedded system
The peak intensity ratios of [M] +. vs. [MH] + were measured in the fast atom bombardment (FAB) mass spectra of readily available test compounds with 3‐nitrobenzyl alcohol as the matrix. For simple aromatic amines, the ratio increases as the ionization energy of the substrate decreases. 4‐Substituted benzophenones showed preferential formation of [MH] + ions, regardless of the nature of the substituents. This is probably due to the fact that the benzophenoes have carbonyl groups which can form hydrogen bonds with the matrix molecule. The peak intensity ratio is roughly proportional to the Hammett σ +. Among 4‐substituted biphenyls, both bromo and chloro substituents afforded abnormally high peak intensity ratios. The effects of the substituents in these compounds are discussed semi‐quantitatively in terms of the Hammett correlation and the hard and soft acids and bases principle. The mechanism of ion formation in FAB and chemical ionization (CI) ion sources appeared to be different because some of the compounds studied showed an intense [M] +. peak with a relatively weak [MH] + peak in FAB spectra but exhibited a strong [MH] + peak in ordinary CI spectra.