Gas-phase Protonation of Pyridine. A Variable-time Neutralization-Reionization andAb InitioStudy of Pyridinium Radicals
✍ Scribed by Nguyen, Viet Q.; Tureček, František
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 472 KB
- Volume
- 32
- Category
- Article
- ISSN
- 1076-5174
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✦ Synopsis
Gas-phase protonation of pyridine with and under thermal conditions CH 3 NH 3 ', NH 4 ', t-C 4 H 9 ', H 3 O' CH 5 ' was studied by variable-time neutralization-reionization mass spectrometry and ab initio calculations. N-Protonation was found to occur exclusively for through and predominantly for The CH 3 NH 3 ' H 3 O' CH 5
'. calculated MP2/6-311G(2d,p) energies gave the proton affinities of N, C-2, C-3 and C-4 in pyridine as 924, 658, 686 and 637 kJ mol-1, respectively, which were in good agreement with previous experimental and theoretical results. Vertical neutralization of the N-protonated isomer (1H') was accompanied by moderate Franck-Condon e †ects that deposited 20-21 kJ mol-1 in the 1H-pyridinium radicals formed. was calculated by (1H~) 1 H ŨMP2/6-311G(2d,p) and B3LYP/6-311G(2d,p) to be a bound species in its ground electronic state. A substantial fraction of stable was detected in the spectra, which depended on the precursor ion internal energy. Deuterium 1Hl abeling showed a speciÐc loss of the N-bound hydrogen or deuterium in the radicals. The speciÐcity increased with increasing internal energy in the radicals and decreasing contribution of ion dissociations following reionization. Variable-time measurements established speciÐc loss of the N-bound deuterium also in dissociating low-energy Loss of hydrogen from 1H' cations following reionization was highly endothermic and was accompanied by 1D~. rearrangements that partially scrambled the ring hydrogens.