Thioglycollates and ß-thiopropionates with SH and/or CO2H groups yield pronounced (M-H)- ions in their negative ion spectra, not molecular negative ions as we previously reported. Compounds containing R1-S-CH2- functionality (R1 = alkyl or aryl) undergo a cleavage to S to yield R1S- and -S-CH2-ions. Hydrogen rearrangements are rare but thioglycollates R1SCH2CO2H characteristically eliminate R1SH to yield CH2CO2-. Fragment negative ions generally do not contain enough excess energy to allow decomposition, so we have studied their collision induced dissociations. Simple cleavage reactions are usual: for example BuSCH2CO2- decomposes to yield both BuS- and BuSCH2-. Group migration to sulfur is also observed; for example, ions -SCH2CO2R2 (R2 = alkyl or aryl) eliminate carbon dioxide to produce R2SCH2- as the major product.
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Bowie et al. (1984) studied this question.