Formation and characterization of methoxy isothiocyanate (CH_3ON=C=S) and methyl cyanate N-sulfide (CH_3OC ident to N~+-S~-) as radical cations and neutrals in the gas phase

摘要

Dissociative ionization of heterocyclic precursors has provided a convenient source of isomeric [CH_3O,C,N,S]~(centre dot +) radical cations. Metastable ion (MI), collisional activation (CA), neutralization-reionization (NR) spectra, and ion-molecule reactions, performed in a hybrid tandem mass spectrometer of sectors-quadrupole-sectors configuration, have demonstrated the isothiocyanate, CH_3ON=C=S~(centre dot +) a, and the nitrile N-sulfide, CH_3OC ident to N-S~(centre dot +) b, connectivities. For the sake of comparison, a potential precursor of the isocyanate, CH_3SN=C=O~(centre dot +) c, was also investigated. The gas phase stability of the corresponding neutral molecules is indicated by the NR and NR/CA spectra. In addition, consecutive collisional activation processes (MS/MS/MS spectra) were used to characterize the structures of metastable ions which, in several cases, were found to be different from the corresponding ions generated in the ion source. Calculated ionization energies and enthalpies of reaction with NO~(centre dot) (at the G2(MP2,SVP) level) support the experimental characterization of ions a and b.