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DOI: 10.1039/A605638E (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 2, 1997, 1221-1234

Direct evidence for anchimeric assistance in alcohol elimination from gas-phase MH+ ions of 1,4-dialkoxycyclohexanes under chemical ionisation. Experiment and theory

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Ronit Shvily, Thomas Müller, Yitzhak Apeloig and Asher Mandelbaum

Abstract

trans-1,4-Dialkoxycyclohexanes afford very abundant [MH - ROH]+ ions upon chemical ionisation (CI), in contrast to the cis-isomers, suggesting anchimeric assistance in the alcohol elimination from the MH+ ions of the trans-diethers. Collision induced dissociation (CID) measurements of the [MH - ROH]+ ions, obtained from various suitably deuterium labelled stereoisomeric 1-ethoxy-4-methoxycyclohexanes, indicate formation of symmetrical bicyclic ethyl and methyl oxonium ions by an anchimerically assisted alcohol elimination from the trans-diethers. On the other hand these measurements suggest that the cis-isomers afford isomeric monocyclic O-protonated 4-alkoxycyclohexene cations, in which the hydrogens at positions 2 and 3 (as well as those at positions 5 and 6, and 1 and 4) are not equivalent. The two results, namely the symmetrical bicyclic structure and the high abundance of the [MH - ROH]+ ions in the CI mass spectra of the trans-diethers, in contrast to the non-symmetrical monocyclic structure and low abundance of these ions in the cis-isomers, are suggested to be direct evidence for anchimeric assistance in a gas-phase ion dissociation process. Ab initio calculations at the MP3/6-31G*//6-31G* level support the anchimerically assisted elimination mechanism observed in trans-1-ethoxy-4-methoxycyclohexane, but also show that the energy difference between the anchimerically assisted and non-assisted elimination mechanisms is small (ca. 2–3 kcal mol-1) (1 cal = 4.184 J).

References

  1. A. Mandelbaum, in Stereochemistry, ed. H. Kagan, Thieme, Stuttgart, 1977, vol. 1, p. 138, and references cited therein Search PubMed.
  2. A. Mandelbaum, Mass Spectrom. Rev., 1983, 2, 223 CAS.
  3. (a) F. Turecek, Collect. Czech. Chem. Commun., 1987, 52, 1928 CAS; (b) F. Turecek, Int. J. Mass Spectrom. Ion Processes, 1991, 108, 137 CrossRef CAS.
  4. A. G. Harrison, Chemical Ionisation Mass Spectrometry, 2nd edn., CRC Press, Boca Raton, Florida, 1992, p. 108 and references cited therein Search PubMed.
  5. R. D. Bowen, M. J. Harrison, D. Neill and S. E. Susan, J. Chem. Soc., Chem. Commun., 1991, 1346 RSC.
  6. M. Vairamani, M. Saraswathi and K. V. Siva Kumar, Org. Mass Spectrom., 1992, 27, 27 CAS.
  7. J. March, Advanced Organic Chemistry, 4th edn., Wiley, New York, 1992, pp. 308–320 and references cited therein Search PubMed.
  8. C. C. Van de Sande, S. Z. Ahmad, F. Borchers and K. Levsen, Org. Mass Spectrom., 1978, 13, 666 CAS.
  9. Related anchimerically assisted bimolecular substitution reactions in gas-phase ions have been reported under radiolytic conditions: (a) G. Angelini and M. Speranza, J. Am. Chem. Soc., 1981, 81, 3792 CrossRef; (b) G. Angelini and M. Speranza, J. Am. Chem. Soc., 1981, 81, 3800 CrossRef.
  10. (a) C. C. Van de Sande, Tetrahedron, 1976, 32, 1741 CrossRef CAS; (b) Van de Sande, Org. Mass Spectrom., 1976, 11, 121.
  11. C. C. Van de Sande, Org. Mass Spectrom., 1976, 11, 130 CAS.
  12. C. C. Van de Sande and F. W. McLafferty, J. Am. Chem. Soc., 1974, 97, 2298.
  13. F. W. McLafferty and F. Turecek, Interpretation of Mass Spectra, 4th edn., University Science Books, Mill Valley, California, 1993, sections 8.3 and 8.11 Search PubMed.
  14. C. M. Orlando, M. George and M. L. Gross, Org. Mass Spectrom., 1993, 28, 1184.
  15. (a) P. Ashkenazi, B. Domon, A. L. Gutman, A. Mandelbaum, D. Mueller, W. J. Richter and D. Ginsburg, Isr. J. Chem., 1989, 29, 131 CAS; (b) A. Mandelbaum, Adv. Mass Spectrom., 1995, 13, 227 Search PubMed.
  16. (a) M. Attina, F. Cacace and A. Marzio, J. Am. Chem. Soc., 1989, 111, 6004 CrossRef CAS and references cited therein; (b) P. M. Viruela-Martin, I. Nebot, R. Viruela-Martin and J. Planelles, J. Chem. Soc., Perkin Trans. 2, 1986, 49 Search PubMed.
  17. J. S. Splitter and F. Turecek, Applications of Mass Spectrometry to Organic Stereochemistry, VCH Publishers, New York, 1993, pp. 144, 437, 443, 448, 450, and references cited therein Search PubMed.
  18. (a) D. S. Noyce and B. R. Thomas, J. Am. Chem. Soc., 1957, 79, 755 CrossRef CAS; (b) N. Mori, J. Chem. Soc. Jpn., 1960, 33, 1332 CAS.
  19. R. Shvily, T. Müller, Y. Apeloig and A. Mandelbaum, in preparation.
  20. For a description of the computational methods used see: W. J. Hehre, L. Radom, P. v. R. Schleyer and J. A. Pople, Ab initio Molecular Orbital Theory, Wiley-Interscience, New York, 1986 Search PubMed.
  21. (a) P. C. Hariharan and J. A. Pople, Chem. Phys. Lett., 1972, 66, 217 CrossRef CAS; (b) M. M. Francl, W. J. Pietro, W. J. Hehre, J. S. Binkley, M. S. Gordon, D. J. DeFrees and J. A. Pople, J. Chem. Phys., 1982, 77, 3654 CrossRef CAS; (c) J. B. Foresman and A. Frisch, Exploring Chemistry with Electronic Structure Methods, Gaussian Inc., Pittsburgh, PA, 2nd edn. 1996 Search PubMed.
  22. GAUSSIAN 92, Revision B.3, M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Patterson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Otiz, J. B. Foresma, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Repogle, J. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. DeFrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez and J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1995.
  23. (a) C. Gonzalez and H. B. Schlegel, J. Phys. Chem., 1989, 90, 2154 CrossRef; (b) C. Gonzalez and H. B. Schlegel, J. Phys. Chem., 1990, 94, 5523 CrossRef CAS.
  24. C. Møller and M. S. Plesset, Phys. Rev., 1934, 46, 618 CrossRef CAS.
  25. An NMR study showed that in solution the diaxial: diequatorial conformers concentration ratio was 15∶85 in pyridine and 2∶98 in water: W. F. Trager, B. J. Nist and A. C. Huitric, J. Pharm. Sci., 1967, 56, 698 Search PubMed.
  26. (a) For a review see: F. R. Jensen and C. H. Bushweller, Adv. Alicyclic Chem., 1971, 3, 139 Search PubMed; (b) R. J. Abraham and Z. L. Rossetti, J. Chem. Soc., Perkin Trans. 2, 1973, 582 RSC.
  27. Early extended Hückel MO calculations suggested that the diequatorial conformer is more stable than the diaxial conformer by 1.0 kcal mol–1: Yu. A. Zhdanov and E. N. Malysheva, Carbohydr. Res., 1972, 24, 87 Search PubMed.
  28. C. Guenat, R. Houriet, D. Stahl and F. J. Winkler, Helv. Chim. Acta, 1985, 68, 1647 CrossRef CAS.
  29. Dixon and Komornicki (D. A. Dixon and A. Komornicki, J. Phys. Chem., 1990, 94, 5630) found at the MP2/tzp level of theory a somewhat higher barrier (12 kcal mol–1) for the conversion of the chair conformation of cyclohexane to the twisted boat conformation than we calculated for the conversion of diax-10t to 14. We believe that this is due to the stabilisation of TS3 relative to diax-10t by the more favourable electrostatic interaction between the positively charged carbon and the 4-hydroxy group in the developing twist-boat conformation of TS3 Search PubMed.
  30. 17 serves as a model for estimating more accurately the effects operating in these protonated 4-methoxycyclohexanols. In the CIMS experiment preferential protonation will occur at the methoxy group, which has a higher proton affinity.
  31. G. S. Hammond and J. Warkentin, J. Am. Chem. Soc., 1961, 83, 2554 CrossRef CAS.
  32. H. C. Brown and B. C. Subba Rao, J. Am. Chem. Soc., 1959, 81, 6423 CrossRef CAS.
  33. O. Averin and A. Mandelbaum, unpublished results.
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