Characterization of the C3H 6O (+·) ion from 2-methoxyethanol. Mixture analysis by dissociation and neutralization-reionization

G3(MP2) study of the C3H6O+* isomers fragmented from 1,4-dioxane+*

The fragmentation process of ionized 1,4-dioxane and the reactions between the C3H6O+* ions, one of the major fragments, and various reactants (including acetonitrile, formaldehyde, ethylene, and propene) have been studied experimentally with mass spectrometry. In the present work, G3(MP2) calculations were carried out to investigate these processes theoretically. In agreement with experiment, isomers CH3OCHCH2+* (1) and *CH2CH2OCH2+ (2) were found to be the C3H6O+* ions fragmented from ionized 1,4-dioxane, with 2 being the major product. The mechanisms of the formation of 1 and 2 were successfully established. In addition, the characteristic reactivities, as well as the corresponding reaction mechanisms, of both isomers were rationalized with the aid of calculations. Finally, a minor reaction between isomer 2 and propene was identified, and the presence of the product of this reaction was found to be useful in explaining the aforementioned mass spectrometric data.

The distonic ion (·)CH 2CH 2CH (+)OH, keto ion CH 3CH 2CH=O (+·), enol ion CH 3CH=CHOH (+·), and related C 3H 6O (+·) radical cations. Stabilities and isomerization proclivities studied by dissociation and neutralization-reionization

Metastable ion decompositions, collision-activated dissociation (CAD), and neutralization-reionization mass spectrometry are utilized to study the unimolecular chemistry of distonic ion (·)CH2CH2CH(-)OH (2(+·)) and its enol-keto tautomers CH3CH=CHOH(-·) (1 (+·)) and CH3CH2CH=O (+·) (3(+·)). The major fragmentation of metastable 1(+·)-3(+·) is H(·) loss to yield the propanoyl cation, CH3CH2C≡O(+). This reaction remains dominant upon collisional activation, although now some isomeric CH2=CH-CH(+) OH is coproduced from all three precursors. The CAD and neutralization-reionization ((+)NR(+)) spectra of keto ion 3 (+·) are substantially different from those of tautomers 2(+·) and 1(+·). Hence, 3(+·) without sufficient energy for decomposition (i. e. , "stable" 3(+·)) does not isomerize to the ther-modynamically more stable ions 2(+·) or 1(+·), and the 1,4-H rearrangement H-CH2CH2CH=O(+·)(3 (+·)) → CH2CH2CH(+) O-H (2 (+·)) must require an appreciable critical energy. Although the fragment ion abundances in the (+) NR (+) (and CAD) spectra of 1 (+·) and 2 (+·) are similar, the relative and absolute intensities of the survivor ions (recovered C3H6O(+·) ions in the (+)NR(+) spectra) are markedly distinct and independent of the internal energy of 1 (+·) and 2 (+·). Furthermore, 1 (+·) and 2 (+·) show different MI spectra. Based on these data, distonic ion 2 (+·) does not spontaneously rearrange to enol ion 1 (+·) (which is the most stable C3H6O(+·) of CCCO connectivity) and, therefore, is separated from it by an appreciable barrier. In contrast, the molecular ions of cyclopropanol (4 (+·)) and allyl alcohol (5 (+·)) isomerize readily to 2 (+·), via ring opening and 1,2-H(-) shift, respectively. The sample found to generate the purest 2 (+·) is α-hydroxy-γ-butyrolactone. Several other precursors that would yield 2 (+·) by a least-motion reaction cogenerate detectable quantities of enol ion 1 (+·), or the enol ion of acetone (CH2=C(CH3)OH(+·), 6 (+·)), or methyl vinyl ether ion (CH3OCH=CH 2 (+·) , 7 (+·)). Ion 6 (+·) is coproduced from samples that contain the -CH2-CH(OH)-CH2- substructure, whereas 7 (+·) is coproduced from compounds with methoxy substituents. Compared to CAD, metastable ion characteristics combined with neutralization-reionization allow for a superior differentiation of the ions studied.