Decarbonylation of the 2-Hydroxypyridine Radical Cation: A Computational Study

Abstract

The potential energy surface (PES) for the dissociation of the 2-hydroxypyridine (2-HP) radical cation was determined from G3//B3LYP calculations, including the loss of CO, HCN, and HNC. The formation of the 1H-pyrrole radical cation by decarbonylation through a more stable tautomer, the 2-pyridone (2-PY) radical cation, was the most favorable dissociation pathway. Kinetic analysis by the Rice-Ramsperger-Kassel-Marcus model calculations was carried out based on the obtained PES. It is proposed that the dissociation occurs after a rapid tautomerization to 2-PY•+, and that most of the ions generated by ionization of 2-HP have the structure of 2-PY•+ at equilibrium above the tautomerization barrier.

Dissociation Mechanism of the 3-Hydroxypyridine Radical Cation: A Computational Study

“…More interesting routes have been found in the dissociations of aromatic molecular ions containing a heteroatom(s) such as N, O, P, S, As, etc. [4][5][6][7][8][9][10][11][12][13][14][15][16] For example, several dissociation pathways have been proposed for the metastable dissociations of three isomeric methylpyridine molecular ions, which include ring cleavage, expansion, and contraction. 12 The dissociations of three isomeric hydroxypyridine (HP) radical cations (Scheme 1), which are isoelectronic with the toluene cation, have been studied using mass spectrometry (MS) and theoretical means.…”

“…12 The dissociations of three isomeric hydroxypyridine (HP) radical cations (Scheme 1), which are isoelectronic with the toluene cation, have been studied using mass spectrometry (MS) and theoretical means. [13][14][15][16] A striking difference in the electron ionization (EI) mass spectra of the three isomer HPs is the relative abundance of the peaks at m/z 67 and m/z 68, which mainly correspond to the losses of CO and HCN (or HNC), respectively. Their abundance ratios are close to one in the EI mass spectra of both 3-and 4-HP, whereas the peak at m/z 67 is much stronger than the peak at m/z 68 in the EI mass spectrum of 2-HP.…”

“…17 In the collision-induced dissociation (CID) spectra of the three isomeric HP cations, similar patterns are observed for the m/z 67 and m/z 68 peaks. 14 In a computational study, we showed that the main product ion in the metastable dissociation of 2-HP +• is the 1H-pyrrole radical cation (1H-PR +• ) formed by the loss of CO. 16 For the dissociation of 4-HP +• , Jobst et al 15 proposed that the ions with m/z 67 and m/z 68 result from the formation of the acyclic C 4 H 5 N +• and C 4 H 4 O +• ions by the losses of CO and HNC, respectively.…”