The unimolecular chemistry of [1,2‐propanediol]+˙: a rationale in terms of hydrogen‐bridged radical cations

By combining results from a variety of mass spectrometric techniques (metastatle ion, collisional activation, collision‐induced dissociative ionization, neutralization–reionization spectrometry and appearance energy measurements) and the classical method of isotopic labelling, a unified mechanism is proposed for the complex unimolecular chemistry of ionized 1,2‐propanediol. The key intermediates involved are the stable hydrogen‐bridged radical cations [CH2C(H)H…︁O…︁O(H)CH3]+˙, which were generated independently from [4‐methoxy, 1‐butanol]+˙ (loss of C2H4) and [1‐methoxyglycerol]+˙ (loss of CH2O), [CH3CO…︁H…︁O(H)CH3]+˙ and the related ion‐dipole complex [CH2C(OH)CH3/H2O]+˙. The latter species serves as the precursor for the loss of CH3˙ and in this reaction the same non‐ergodic behaviour is observed as in the loss of CH3˙ from the ionized enol of acetone.