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Eur. J. Mass Spectrom. 1, 545 - 559 (1995) |
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The chemistry of ionized ethyl glycolate, HOCH2CO2C2H5·+, and its enol isomer, HOCH=C(OH)OC2H5·+. Formation of ionized and neutral trihydroxyethylene | ||
Dennis Suh, James T. Francis and Johan K. Terlouw* |
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ABSTRACT: | ||
The unimolecular reactions of ionized ethyl glycolate, HOCH2CO2C2H5"+, and its enol isomer, HOCH=C(OH)OC2H5"+, have been studied by a variety of techniques including 2H-, 13C- and 18O-labelling experiments, kinetic energy release information, analysis of collision-induced dissociation and neutralizationreionization mass spectra and thermochemical measurements. The metastable ionized enol eliminates C2H4 essentially exclusively by ß-hydrogen transfer to give (HO)2C=CHOH"+, which itself expels H2O with very high selectivity (~99%). The metastable ionized keto isomer also eliminates C2H4, but minor amounts (~5%) ofcompeting fragmentations resulting in expulsion of H2O, HOCO" and HCO" are also observed. Moreover, in this case, loss of C2H4 no longer involves specific ß-hydrogen transfer. This behavior is interpreted in terms of rearrangement of the ionized keto form via a 1,5-H shift to the distonic ion HOCH2C+(OH)OCH2CH2", which undergoes a further 1,5-hydrogen shift to form HOCH=C(OH)OC2H5"+, from which C2H4 is lost to give (HO)2C=CHOH"+. The chemistry of these C4H8O3"+ species, in which unidirectional tautomerism of HOCH2CO2C2H5"+ to HOCH=C(OH)OC2H5"+ via two 1,5-H shifts is important, contrasts sharply with the behavior of the lower homologues, HOCH2CO |
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