Structural and substituent effects on [M]+.vs. [MH]+ formation in fast atom bombardment mass spectra of simple organic compounds
✍ Scribed by Hisao Nakata; Katsunori Tanaka
- Publisher
- John Wiley and Sons
- Year
- 1994
- Tongue
- English
- Weight
- 567 KB
- Volume
- 29
- Category
- Article
- ISSN
- 1076-5174
No coin nor oath required. For personal study only.
✦ Synopsis
The peak intensity ratios of [ M ] +' YS. [ 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. CSubstituted benzophenones showed preferential formation of [MH]' ions, regardless of the nature of the substituents. This is probably due to the fact that the benzophenones have carbonyl groups which can form hydrogen bonds with the matrix molecule. The peak intensity ratio is roughly proportional to the Hammett c r ' . 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 [MI+* peak with a relatively weak [MHI' peak in FAB spectra but exhibited a strong [ MH] + peak in ordinary CI spectra. a Unless stated otherwise, If and PA values were taken from Ref. 25 and pK, values of the conjugate acid of each amine from Ref. 26. 6 Diphenylamine 691 890" 1.1 Ref. 27. Estimated value from PA of 1 and 7.