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DOI: 10.1039/A903161H (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 2, 1999, 1663-1668

Conformational analysis, Part 32.† NMR, solvation and theoretical investigation of conformational isomerism in 3-fluorobutan-2-one and 3,3-difluorobutan-2-one

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Raymond J. Abraham, Claudio F. Tormena and Roberto Rittner

Abstract

The solvent and temperature dependence of the 1H and 13C NMR spectra of 3-fluorobutan-2-one (FB) and 3,3-difluorobutan-2-one (DFB) are reported and the 4JHF, 1JCF and 2JCF couplings analysed using ab initio calculations and solvation theory. The solvent dependence of the IR spectra (carbonyl band) was also measured. In FB, ab initio theory at the 6-31G**/MP2 level gives only two energy minima for the cis (F–C–C[double bond, length half m-dash]O 22°) and trans (F–C–C[double bond, length half m-dash]O 178°) rotamers. The gauche rotamer was not a minimum in the energy surface. Assuming only the cis and trans forms, the observed couplings when analysed by solvation theory lead to the energy difference (Ecis – Etrans) between the cis and trans rotamers of 3.7 kcal mol–1 in the vapour phase, decreasing to 2.5 kcal mol–1 in CCl4 and to 0.1 kcal mol–1 in DMSO. In all solvents used the trans rotamer is more stable than the cis. The vapour state energy difference compares very well with that calculated [3.67 kcal mol–1 including a zero-point energy correction (ZPE)]. In DFB ab initio calculations at this level and also at (6-311G**/MP2 and ZPE) gave only one minimum in the potential energy surface corresponding to the cis rotamer (C–C–C[double bond, length half m-dash]O 0°). The 1H and 13C NMR data, 4JHF, 1JCF and 2JCF couplings do not change with solvent confirming that there is only one rotamer in solution for DFB, in agreement with the ab initio calculations.

References

  1. R. J. Abraham, I. Castellazzi, F. Sancassan and T. A. D. Smith, J. Chem. Soc., Perkin Trans. 2, 1999, 99 RSC.
  2. E. Saegebarth and E. B. Wilson, J. Chem. Phys., 1967, 46, 3088 CrossRef CAS.
  3. B. P. van Eijck, G. van der Plaats and P. H. van Roon, J. Mol. Struct., 1972, 11, 67 CrossRef CAS.
  4. J. R. Durig, H. V. Phan, J. A. Hardin and T. S. Little, J. Chem. Phys., 1989, 90, 6840 CrossRef CAS.
  5. J. R. Durig, J. A. Hardin, H. V. Phan and T. S. Little, Spectrochim. Acta, Part A, 1989, 45, 1239 CrossRef.
  6. R. J. Abraham, A. D. Jones, M. A. Warne, R. Rittner and C. F. Tormena, J. Chem. Soc., Perkin Trans. 2, 1996, 533 RSC.
  7. (a) J. R. Durig, M. Mamula-Bergana and H. V. Phan, J. Raman Spectrosc., 1991, 22, 141 CAS; (b) J. R. Durig, M. Mamula-Bergana and H. V. Phan, J. Mol. Struct., 1991, 242, 179 CrossRef CAS; (c) H. V. Phan, G. A. Guirguis and J. R. Durig, Spectrochim. Acta, Part A, 1993, 49, 1967.
  8. (a) G. J. Karabatsos, D. J. Fenoglio and S. S. Lande, J. Am. Chem. Soc., 1969, 91, 3572 CrossRef CAS; (b) D. F. Ewing, J. Chem. Soc., Perkin Trans. 2, 1972, 701 RSC.
  9. B. L. Shapiro, H. L. Lin and M. D. Johnston, Jr, J. Magn. Reson., 1973, 9, 305 CAS.
  10. GAUSSIAN94 (Revision B.3)M. J. Frisch, G. W. Trucks, H. B. Schlegel, J. R. Cheeseman, P. M. W. Gill, M. W. Wong, J. B. Foresman, B. G. Johnson, M. A. Robb, E. S. Replogle, R. Gomperts, J. L. Andres, K. Raghavachavi, J. S. Blinkley, C. Gonzalez, R. L. Martin, D. J. Fox, D. J. Defrees, J. Baker, J. P. Stewart, T. Keith, G. A. Petersson, J. A. Montgomery, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. Cioslowski, B. B. Stefanov, A. Nanayakkara, M. Challacombe, C. Y. Peng, P. Y. Ayala, W. Chen, M. Head-Gordon, J. A. Pople, Gaussian Inc., Pittsburgh, PA, 1995.
  11. R. J. Abraham and E. Bretschneider, in Internal Rotation in Molecules, ed. W. J. Orville-Thomas, Academic Press, London, 1974, ch. 13 Search PubMed.
  12. R. J. Abraham and L. Griths, Tetrahedron, 1981, 37, 575 CrossRef CAS.
  13. R. J. Abraham, P. Leonard, T. A. D. Smith and W. A. Thomas, Magn. Reson. Chem., 1996, 34, 71 CrossRef CAS.
  14. R. J. Abraham, G. H. Grant, I. S. Haworth and P. E. Smith, J. Comput. Aided Mol. Des., 1991, 5, 21 CAS.
  15. J. B. Foresman and A. Frish, Exploring Chemistry with Electronic Structure Methods: A Guide to Using Gaussian, Gaussian, Inc., Pittsburgh, PA, 1993 Search PubMed.
  16. D. P. Wyman and P. R. Kaufman, J. Org. Chem., 1964, 29, 1956 CAS.
  17. A. I. Burmakov, I. V. Stepanov, B. V. Kunshenko, L. N. Sedova, L. A. Alekseeva and L. M. Yagupol'skii, J. Org. Chem. USSR, 1982, 1009.
  18. P. R. Olivato and R. Rittner, Rev. Heteroatom. Chem., 1996, 15, 115 Search PubMed.