Gas‐phase unimolecular chemistry of ethyl butyl ketone cations

Abstract

Mass spectra of the four isomeric ethylbutyl ketones, C2H5CO‐n‐C4H9 (1), C2H5CO‐iso‐C4H9 (2), C2H5CO‐sec‐C4H9 (3) and C2H5 CO‐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: [C2H5C(OH)CHCHCH3]+, [C2H5C(OH)CH2]+˙ and a mixture of [CHOHCHCHC2H5]+ and [CHOHCHC(CH3)2]+, 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 [C2H5C(OH)CHCH3]+˙ and [t‐C4H9CO]+. 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.

Selected Radical Removal from Proton-Bound Dimers. A Strategy for Studying Solvated Distonic Ions

“…These unusual radical cations have been extensively investigated beginning with the first theoretical prediction and successful experimental demonstration of the existence of the distonic methanol ion . Distonic ions, which are often thermochemically more stable than their conventional counterparts, have been shown to be intermediate in many familiar fragmentation reactions of organic ions, e.g., the McLafferty rearrangement . More importantly, their ambident properties, stemming from the separation of the radical and charge sites, have created a new dimension in gas-phase ion chemistry …”

The Chemistry of Solvated Distonic Ions: Preparation, Isomerization, and Fragmentation

“…The chemistry of distonic ions , has been extensively investigated since their prototype, the distonic methanol ion, was prepared and characterized in 1982. Distonic ions have been identified as stable products 1 or intermediates of the unimolecular fragmentation of gas-phase ions. Although distonic ions are generally more stable than the corresponding molecular ions, these isomers are usually separated by a high energy barrier, and their interconversions do not take place below a dissociation limit of one or another of the species.…”

A Quantum Chemical Study of the Protonation of Phenylphosphine and its Halogenated Derivatives

“…From the beginning, we have taken advantages of the building-up at Mons of a large scale tandem mass spectrom-eter, a Micromass AutoSpec 6F [33][34] combining six sectors of EBEEBE geometry which has been, and still is, used to perform our MS experiments. Later, an rf-only quadrupole collision cell (q) fitted with retardation and acceleration lenses has been added into the spectrometer giving a unique EBEq-EBE configuration.…”