12  Organic gas-phase ion chemistry

Abstract

Gas-phase ion chemistry is a useful approach for the investigation of physical organic chemistry and the study of reactivity, structure, and thermochemical properties of ionic and neutral organic substrates. This review summarizes the physical organic chemistry studies utilizing gas-phase ion chemistry reported in the past year. Among the more significant advances reported in the past year included a report of the reactivity of p-benzyne by Kenttämaa and co-workers, 1 a comparison of the S N 2 reaction in the gas-phase and in solution by Brauman and co-workers, 2 and a full characterization of the structure and energetics of cyanocarbene. 3,4 Information learned from these gas-phase ion studies includes: 1) p-benzyne undergoes radical reactions but also reacts as a weak electrophile; 2) unlike what is found in solution, steric bulk does not significantly affect the barriers for S N 2 reactions of halogenated nitriles; and 3) HCCN is a "floppy" molecule with a triplet ground state and a singlet excited state that is ca. 50 kJ mol Ϫ1 higher in energy.Papers included in this review were selected 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. Our emphasis in this work is on the chemistry that is observed, and information regarding the instrumental technique is only provided in situations where it is critical for understanding the results. The majority of the studies were carried out by using Fourier transform-ion cyclotron resonance (FT-ICR), quadrupole ion trap, or flowing afterglow techniques. We have generally not included papers regarding ionization fragmentation patterns, unless the work was part of broader studies. Studies of organometallic ions were generally not included if the chemistry was dominated by the metal center. Moreover, computational studies were also not included unless they provided significant insight into specific experimental results.It was with some trepidation that we restrict the number of biological studies included in this paper. Recent advances in mass spectrometric capabilities have led to numerous fundamental studies of the properties of biologically relevant molecules. In this work, we generally have only included the studies of the simplest biological molecules, amino acids, nucleic acids, and monosaccharides. It is clear that many more future mass spectrometric studies will likely involve biological substrates. As such, it is anticipated that future versions of this report may need to be expanded to include more biologically relevant material.The articles summarized in this review are organized into broad classifications: 420

Experimental infrared spectra of Cl−(ROH) (R = H, CH3, CH3CH2) complexes in the gas-phase

“…S N 2 reactions have been the topic of many gas-phase studies, both computationally and experimentally, for many years [1][2][3][4][5][6][7][8][9][10] and are becoming well understood. This understanding can, perhaps, be applied to manipulate solution-phase reactions.…”

Furofuranic glycosylated lignans: a gas‐phase ion chemistry investigation by tandem mass spectrometry

“…Energy‐resolved CAD mass spectra give essential information about the integrated energetic picture of dissociation mechanisms and represent a useful tool for the gas‐phase ion chemistry study of the reactivity, structure, and thermochemical properties of ionic and neutral compounds 21–26…”

12 Organic gas-phase ion chemistry

“…This increase in rate suggests the radical electrons remain coupled and preferentially react through an ionic pathway, as opposed to a radical pathway. In contrast, the reaction rates of the biradicals with predicted triplet states (9)(10)(11) are similar to those of their analogous monoradicals, with small differences in products accounted for by rapid radical-radical recombination of the initial reaction products. Greater reactivity towards hydrogen donors occurs with radicals that have the charge in the same ring system as the radical site, as polar effects play an important role in the reactivity of p,p-biradicals.…”

“…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, [7][8][9][10][11] we separate the reactivity studies into multiple sections including one specifically addressing stereoselective reactivity and stereochemical analysis, and one addressing structures and energetics of biologically relevant molecules.…”