Abstract The mass spectra of S-alkyl-β-thiopropionic acids contain skeletal-rearrangement ions which arise by hydroxyl migration to a carbonium-ion centre followed by elimination of a neutral molecule (eg ketene or formaldehyde). In contrast, those of methyl S-alkyl-β- thiopropionates contain peaks which are formed by methoxyl migration to sulphur, followed by loss of ketene.
