Site of Protonation in Gaseous Five-Membered Ring Systems C4H4X(X=NH,O,S,CH2)
The study of acid-base properties of isolated systems have resulted in a fast growing output of data obtained in high pressure mass spectrometers and in low pressure ion cyclotron resonance spectrometers (ICR), (see Ref. 1 for recent reviews). These studies provide the basis for evaluating intrinsic substituent effects and Taft et al.  have recently stressed the predominance of polarization effects over polar (inductive) effects in stabilizing charged species. Subsequent comparison of gas phase and condensed phase data have the potentiality of disclosing solvent effects operating in the condensed phase . While the understanding of the basic properties of monofunctional compounds is a relatively unambiguous matter, the situation becomes evidently more complex in multifunctional systems. Recent examples of the latter are provided by the ketene molecule in which it was found that the carbonyl group is less basic than the methylene group by 18 ± 8 kcal/mol , and also by enamine systems where the N-site was found to be less basic than the p-C-site by approximately 9 kcal/mol .
KeywordsProton Affinity Double Resonance Proton Affinity Proton Affinity Deuterated Sample Double Resonance Experiment
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- 1.“Gas-Phase Ion Chemistry”, M.T. Bowers, Ed., Chapters 9–11, Academic Press, New York (1979).Google Scholar
- 3.E.M. Arnett, Acc. Chem. Res. 6 (1973) 404Google Scholar
- 5.R. Houriet, J. Vogt and E. Haselbach, Chimia 34 (1980) 277.Google Scholar
- 7.R. Houriet, H. Schwarz, W. Zummack, J. G. Andrade and P.v.R. Schleyer, Nouv. J. Chim., in press.Google Scholar
- 11.See for example, T.A. Lehman and M.M. Bursey, “Ion Cyclotron Resonance Spectrometry”, Wiley-Interscience, New York (1976).Google Scholar
- 13.For leading articles on “homoconjugation” see P.R. Story and B.C. Clark Jr., in “Carbonium Ions”, p. 1007, G.A. Olah and P.V.R. Schleyer, eds., Wiley-Interscience, New York (1972) and references cited therein.Google Scholar
- 14.F.P. Lossing and J.C. Traeger, J. Am. Chem. Soc. 97 (1975) 1579.Google Scholar
- 15.J.D. Cox and G. Pilcher, “Thermochemistry of Organic and Organometallic Compounds”, Academic Press, New York (1970).Google Scholar