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

Abstract 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 [CH 2 C(H)H…︁O…︁O(H)CH 3 ] + ˙, which were generated independently from [4‐methoxy, 1‐butanol] + ˙ (loss of C 2 H 4 ) and [1‐methoxyglycerol] + ˙ (loss of CH 2 O), [CH 3 CO…︁H…︁O(H)CH 3 ] + ˙ and the related ion‐dipole complex [CH 2 C(OH)CH 3 /H 2 O] + ˙. The latter species serves as the precursor for the loss of CH 3 ˙ and in this reaction the same non‐ergodic behaviour is observed as in the loss of CH 3 ˙ from the ionized enol of acetone.