FUNCTIONAL-GROUP INTERACTIONS IN THE FRAGMENTATION OF PROTONATED AND METHYLATED SUCCINIC ACID-DERIVATIVES

The methane chemical ionization (CI) mass spectra of succinic acid mon oamide and monomethyl succinate have been determined. In addition, the unimolecular metastable ion fragmentation reactions and low-energy co llision-induced dissociation reactions of the MH+ and M.CH3+ ions of t hese compounds have been determined. In the CH4 CI mass spectra extens ive fragmentation of the MH+ ions is observed, indicative of functiona l group interactions. An important fragmentation reaction for the prot onated monoamide involves formation of NH4+ and it is suggested that t his occurs through the. intermediacy of a protonated succinic anhydrid e/ammonia ion-neutral complex. The [MH-H2O](+) and [MH-CH3OH](+) fragm ent ions formed in the CH4 CI of monomethyl succinate give collision-i nduced dissociation (CID) spectra which are in agreement with the spec tra obtained for methylated and protonated succinic anhydride, respect ively; these results strongly support the suggestions that the formati on of stable cationated cyclic anhydride structures are one of the fac tors which result in extensive fragmentation of protonated and cationa ted dicarboxylic acid derivatives. The M.CH3+ adduct of succinic acid monoamide gives a CID spectrum which is distinctly different from that obtained for the protonated monomethyl ester of succinic acid monoami de. This result indicates that little addition of CH3+ to the free COO H group of the monoamide occurs. The CID spectrum of the M.CH3+ adduct of monomethyl succinate also shows substantial differences from the C ID mass spectrum of protonated dimethyl succinate. (C) 1998 Elsevier S cience B.V.