Intermediate ion structures in the fragmentation of metastable 3-methylbutan-2-ol radical cations

✍ Scribed by M. George; John L. Holmes

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 434 KB
• Volume: 25
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210251108

✦ Synopsis

Ionized 3-methylbutan-2-01 displays four low-energy fragmentations, loss of CH,' and C,H,' and loss of CH, and C,H, , the latter pair being produced by metastable ion decompositions. The electron-impact, metastableion and collision-induced dissociation mass spectra of I3C and 'H-labelled isotopomers have been recorded, together with appearance energy measurements. It was found that the fast (ion source) losses of CH,' and C,H,' involved only simple bond cleavages between C(l) and C(2) and between C(2) and C(3), respectively, and without any positional interchange of isotopes. The loss of C,H, produces ionized vinyl alcohol containing only C(l) and C(2). The H atoms involved are only those attached to C(l) and C(3). In deuterium-labelled analogues, the deuterium is preferentially located in the propane, e.g. metastable CD,CH(OH)CH(CH,), yields predominantly C,H6D,. On the basis of all the observations, it is proposed that low-energy molecular ions can form a stable proton-bridged molecule-radical complex, [ HOCHCH, -*.H -**&I(CH,),], and that this key intermediate is responsible for the isotope distribution in propane loss and also for the relatively low importance of the lowest energy dissociation, the simple C ( l H ( 2 ) bond cleavage.