Distonic Ion ·CH2CH2SCH+2 and the Isomeric Trimethylene and Propylene Sulfide Radical Cations. Assessment of Structures and Reactivities via Decomposition and Redox Reactions
✍ Scribed by Michael J. Polce; Chrys Wesdemiotis
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 763 KB
- Volume
- 10
- Category
- Article
- ISSN
- 0951-4198
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✦ Synopsis
The distonic radical ion 'CH,CH,SCH,' (l"), generated by dissociative electron ionization of 1,4-dithiane or 1,4-thioxane, is identified in the gas phase by its collisionally activated dissociation (CAD), neutralizationreionization ('NR' ) and charge-reversal ('CR-) mass spectra. The unimolecular chemistry of 1' ' is shown to be substantially different from that of the isomeric, ring-closed, trimethylene sulfide ion (2'7. Hence, a substantial isomerization barrier must separate 1' ' from the thermodynamically more stable 2+*. Charge permutation (i.e. charge-stripping, 'NR' and 'CR-) are far superior, compared to collision-induced fragmentation, for distinguishing 1' ' from 2'*, mainly because the oxidized (1'' and 2" ) and reduced forms (1 and 2 as well as 1-' and 2-7 of these cations have much lower tendencies for isomerization than 1" and 2+' themselves. The diradical 'CH,CH,SCH; (l), formed by neutralization of l'., is found to exist as a bound species, requiring appreciable activation energies for both decomposition to CH2CH2 plus SCH, and ring-closure to 2. The dissociations and redox reactions of the propylene sulfide ion (3+7 are also assessed in this study and clearly indicate that 3'' is a stable C,&S+' isomer. Further, the C3&S'' ions from thiane, 1J-dithiane and 2-methyl-lJ-dithiane are characterized based on their combined CAD, 'NR' and 'CR-spectra. The two 13-dithianes produce ionized trimethylene sulfide, 2' ' . In contrast, thiane gives rise to a C,l&S+' isomer other than 1+'-3+'; the data strongly suggest that this isomer is the 1-propene-1-thiol radical cation, namely CH,CH=CHSH".