Behaviour of salts of very strong proton-sponge bases in the gas phase: Extended proximity effects and maintenance of the hydrogen bridge under soft ionization. An electron impact and liquid secondary ion mass spectrometric/collision-induced dissociation tandem mass spectrometric study
✍ Scribed by Marina Rentzea; Fredy Kühn; Heinz A. Staab
- Publisher
- John Wiley and Sons
- Year
- 1993
- Tongue
- English
- Weight
- 331 KB
- Volume
- 28
- Category
- Article
- ISSN
- 1076-5174
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✦ Synopsis
The liquid secondary ion mass spectrometry and electron impact ionization fragmentation pathways of 1,9bis(dimethylamino)-2,8-dimethoxy-dibenzofuran (l), a new proton-sponge base with increased steric compression (buttressing) and much higher basicity (pK, = 14.3), and of its monoprotonated (2) and monodeuterated (3) salts were invetigated in a collision-induced dissociation (CID) tandem mass spectrometric study supported by unimolecular linked scans at constant B/E, CID mass-analysed ion kinetic energy spectra and accurate mass measurements. They show an 'extended' proximity effect, involving the stepwise participation of all the four functional groups, in addition to the 'normal' proximity effect involving loss of Me,NH and H. The behaviour of 1 appears to differ in some ways from that of its protonated (2) or deuterated (3) salts. The unprecedented observation of the maintenance of the hydrogen (or deuterium) bridge under soft ionization in the salts of very strong proton-sponge bases, which show buttressing effects in solution, is strong experimental support for the conservation of these buttressing effects in the gas phase, where the protonated (or deuterated) cations of salts such as 2 (or 3) are very stable, H + (or D+) being completely 'sequestered.'