Gas-phase Unimolecular Chemistry of Ethyl Butyl Ketone Cations

Article abstract of DOI:10.1002/oms.1210281034

Mass spectra of the four isomeric ethyl butyl ketones, C2H5CO-n-C4H9 (1), C2H5CO-iso-C4H9 (2), C2H5CO-sec-C4H9 (3) and C2H5CO-t-C4H9 (4), are reported.The structure of the fragment ions produced from precursors of both high and low internal energy were identified by collision experiments in a six-sector mass-spectrometer.Metastable molecular ions 1(+.) and 2(+.) behave identically in expelling CH3(.), C3H6 and C2H5(.) to produce the same fragment ions: (+), (+.) and a mixture of (+) and (+), respectively.The key isomerization step between 1(+.) and 2(+.) is a 1,2-enol-olefin shift.Metastable molecular ions 3(+.) and 4(+.) give essentially ethene and ethyl losses, respectively; the fragment ions are (+.) and (+).Keto-enol isomerization also occurs to a significant extent for ions 1(+.) and 2(+.) and 3(+.).In contrast, 1,2- or 1,3-ethylhydroxycarbene migrations are only marginal processes.