Gas Phase Studies of the Competition between Substitution and Elimination Reactions

Gas phase studies allow for the examination of organic reaction mechanisms in the absence of solvation effects and therefore probe the intrinsic reactivity of the reaction partners. The competition between substitution and elimination reactions has been a topic of interest for decades, but it has been difficult to examine in the gas phase because both pathways generally lead to the same ionic product and cannot be distinguished by mass spectrometry. By using dianions as nucleophiles, the reactions produce two ionic products, one of which identifies the mechanism. With this approach, we have examined a variety of substituent effects on the gas phase competition between substitution and elimination. In addition, we have found that similar processes occur during collisional activation of salt complexes that contain a dianion and a tetraalkylammonium cation. Overall, the results show that the gas phase studies probe the same fundamental features found in the condensed phase and provide valuable insights into reaction mechanisms.