2CO2C2H5·+, and its enol isomer, HOCH=C(OH)OC2H5·+. Formation of ionized and neutral trihydroxyethylene



Full-text Article (Subscribers only)
Full-text article (328 kB)
(subscribers only)

Buy article on-line and get access immediately
Buy article on-line for £11.75
(get immediate access)

Search
Search

Go Back

Eur. J. Mass Spectrom. 1, 545 - 559 (1995)

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*
Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada.
Peter C. Burgers
Hercules European Research Center BV, Nijverheidsweg 60, 3771 ME Barneveld, The Netherlands.
Richard D. Bowen
Chemistry and Chemical Technology, University of Bradford, Bradford, West Yorkshire, BD7 1DP, UK.

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, HOCH2CO2CH3<195>+ and HOCH=C(OH)OCH3"+, for which the analogous tautomerism via 1,4-H shifts does not occur. The mechanism for loss of C2H4 from HOCH=C(OH)OC2H5"+ is essentially the same as that observed for ionized phenyl ethyl ether in that the reaction proceeds via an exothermic proton transfer in an ethyl cationradical complex. Neutralizationreionization experiments show that neutral trihydroxyethylene in the gas phase is a remarkably stable species which does not tautomerize to glycolic acid, HOCH2COOH. Using G2(MP2) theory, the enthalpy of formation, .DELTA.Hf298, of the neutral molecule (most stable conformer) was found to be 449.4 kJ mol1 while that of the corresponding ion was calculated to be 299.6 kJ mol1.

Keywords:

You can now buy this paper on-line in PDF format; it costs only £11.75. Just click on the BUY on-line button. You can pay on-line through a secure server and get access immediately.


© IM Publications
Any problems? E-mail .