14 Organic gas-phase ion chemistry

Abstract

This review summarizes the physical organic chemistry studies utilizing gas-phase ion chemistry in the past year. For more than 20 years, gas-phase ion chemistry has provided insight into mechanisms of chemical reactions through studies of reactivity, structure, and thermochemistry of neutral and ionic substrates. Whereas initial studies often involved the use of simple mass spectrometric methods (by today's standards) of an ion source and a detector, modern methods are more sophisticated, as are the problems being investigated. Thus, in addition to gaining insight into the role that solvation plays in stabilizing ionic structures, as with Kass and Wang's studies of zwitterionic pyridinium carboxylates, or the effect of ionization on reaction potential energy surfaces, as illustrated by the electron-catalyzed Cope rearrangement study by Hammad and Wenthold, gas-phase ion chemistry has been applied to modern, burgeoning areas of chemistry including host–guest chemistry, in the report of “molecular mousetraps” by Beauchamp and co-workers, and abiogenesis, where Cooks and co-workers tout the potential role of ionic serine clusters.As with last year, we identified papers for this review by considering contributions to the standard organic, physical, and mass spectrometry journals. The selected articles are those that address the issue of reactivity and structure of organic molecules. Because our emphasis in this work is on the chemistry that is observed and the main conclusions, information regarding the instrumental technique is generally not provided. Most reactivity studies were carried out by using Fourier transform-ion cyclotron resonance (FT-ICR), quadrupole ion trap, or flowing afterglow techniques, but some studies involved the use of tandem methods. Most of the spectroscopic studies involved the use of photoelectron spectroscopy, or a variation thereof. Even more so than we did last year, we have omitted most papers that are mainly organometallic or theoretical in nature. Yet, despite the more stringent selection, we have included 45 more papers than we did last year.In last year's article, we noted the problem of whether to include biological studies. As with most areas of organic chemistry, the biological influence in gas-phase ion chemistry is undeniable, and evident in all aspects of this review. This year we also include a section on biological studies, which included studies of larger substrates such as peptides.The articles summarized in this review are organized into broad classifications: reactivity, reactive species, spectroscopy, and thermochemistry. As has been traditionally the case with this report, we separate the reactivity studies into multiple sections including one specially addressing stereoselective reactivity and stereochemical analysis, and one addressing structures and energetics of biologically relevant molecules.A 2003 edition of Topics in Current Chemistry had a mass spectrometry focus, with reviews covering aspects of reactivity, metalorganic chemistry and methodology. Many of the topics included in the volume were related to organic mass spectrometry.