Fragmentation reactions in the 1-nitropropane radical cation induced by γ-hydrogen shift: Ab initio study

• Three major fragmentation channels of molecular ion (m/z > 89) of 1-nitropropane were explored.
• Additional support to stepwise manner of McLafferty rearrangement was provided.
• New mechanisms of hydroxyl elimination from 1-nitropropane radical cation were proposed.

Three main primary fragmentation channels of molecular ion (m/z > 89) of 1-nitropropane induced by γ-hydrogen shift: (1) McLafferty rearrangement, (2) formation of nitric oxide and (3) detachment of hydroxyl induced by γ-hydrogen transfer were studied employing ab initio UMP2 level of theory. Gibbs energies for all stationary points were computed using CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVTZ technique. Results obtained in the course of present theoretical study give additional support to stepwise mechanism of McLafferty rearrangement which has recently sparked much argument in the mass spectrometry community. We have performed for the first time, the reaction pathways for hydroxyl loss from ion m/z  89 accompanied by formation of four and five-membered heterocyclic cations with m/z  72. Rice–Ramsperger–Kassel–Marcus (RRKM) theory was employed for calculation of the unimolecular rate constants of fragmentation channels.

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