Spectroscopic and theoretical studies on the conformation of some α-sulfinylacetophenones

Abstract

IR ν_CO and ν_SO frequencies of some α-sulfinylacetophenones [PhC(O)CH₂S(O)R: R = Me 1, Et 2, Prⁱ 3, Ph 4 and Bu^t 5] have been measured and their conformations are estimated with the help of ab initio 6-31G** calculations and X-ray diffraction analyses. The anomalous negative carbonyl frequency shifts for the cis₂ rotamer together with the decrease of the cis∶gauche population ratio in solvents of increasing polarity for compounds 1–4 support the existence of a strong intramolecular interaction between C[double bond, length half m-dash]O and S[double bond, length half m-dash]O dipoles, which stabilizes the cis₂ rotamer more than the π_CO–σ*_C–SO and π*_CO–σ_C–SO orbital interactions stabilize the gauche₃ rotamer. The stability of the cis₂ rotamer is discussed in terms of the electrostatic attraction between the C[double bond, length half m-dash]O and S[double bond, length half m-dash]O dipoles along with the π*_{S [double bond, length half m-dash] O}←n_O(CO) charge transfer which lead to an O_(CO)  · · ·  S_(SO) contact shorter than the sum of the corresponding van der Waals radii. The gauche₂ rotamer of 5 is more stable than the cis₂ one in which steric strain between the carbonyl oxygen atom and the tert-butyl group is present.

References

1. P. R. Olivato and M. G. Mondino, Phosphorus, Sulfur Silicon Relat. Elem., 1991, 59, 219.
2. P. R. Olivato, S. A. Guerrero and E. A. Martins, Phosphorus, Sulfur Silicon Relat. Elem., 1989, 44, 9.
3. H. Lumbroso, D. M. Bertin, P. R. Olivato, E. Bonfada and M. G. Mondino, J. Mol. Struct., 1989, 212, 113.
4. P. R. Olivato, B. Wladislaw and S. A. Guerrero, Phosphorus, Sulfur Silicon Relat. Elem., 1987, 33, 135.
5. P. R. Olivato and S. A. Guerrero, Phosphorus, Sulfur Silicon Relat. Elem., 1992, 66, 207.
6. E. Bonfada, MSc. Thesis, University of São Paulo, Brazil, 1989.
7. G. Distefano, M. Dal Colle, V. Bertolasi, P. R. Olivato, E. Bonfada and M. G. Mondino, J. Chem. Soc., Perkin Trans. 2, 1991, 1195.
8. M. Dal Colle, V. Bertolasi, M. de Palo, G. Distefano, D. Jones, A. Modelli and P. R. Olivato, J. Phys. Chem., 1995, 99, 15 011.
9. E. Bueno, MSc. Thesis, University of São Paulo, Brazil, 1996.
10. G. Distefano, M. Dal Colle, M. de Palo, D. Jones, G. Bombieri, A. Del Pra, P. R. Olivato and M. G. Mondino, J. Chem. Soc., Perkin Trans. 2, 1996, 1661.
11. M. G. Mondino, Ph.D. Thesis, University of São Paulo, Brazil, 1996.
12. P. R. Olivato, S. A. Guerrero and R. Rittner, Phosphorus, Sulfur Silicon Relat. Elem., in the press.
13. G. A. Russel and G. J. Mikol, J. Am. Chem. Soc., 1966, 88, 5498.
14. P. R. Olivato, E. Bonfada and R. Rittner, Magn. Reson. Chem., 1992, 30, 81.
15. K. Griesbaum, A. A. Oswald and B. E. Hudson, Jr., J. Am. Chem. Soc., 1963, 85, 1969.
16. F. Alcudia, I. Fernandez, J. M. LLera and F. Zorrilla, An. Quim., 1988, 84, 333.
17. P. R. Olivato, B. Wladislaw and S. A. Guerrero, Phosphorus, Sulfur Silicon Relat. Elem., 1987, 33, 135.
18. J. Pitha and R. N. Jones, Can. J. Chem., (a) 1966, 44, 3031; (b) 1967, 46, 2347.
19. R. N. Jones and J. Pitha, Natl. Res. Council Can. Bull., 1968, n. 12; 1969, n. 13.
20. J. C. D. Lopes, P. R. Olivato, P. A. M. Vazques and Y. Hase, An. Assoc. Bras. Quim., 1992/1993, 41/42, 87.
21. E. Eliel, N. L. Allinger, S. J. Angyal and G. A. Morrison, Conformational Analysis, Wiley, New York, 1967.
22. GAUSSIAN92: B. Revision, M. J. Frisch, G. W. Trucks, M. Head-Gordon, P. M. W. Gill, M. W. Wong, J. B. Foresman, B. G. Johnson, H. B. Schlegel, M. A. Robb, E. S. Replogle, R. Gomperts, J. L. Andres, K. Raghavachari, J. S. Binkley, C. Gonzales, R. L. Martin, D. J. Fox, D. J. Defrees, J. Baker, J. J. Steward, J. A. Pople, Gaussian 92, Gaussian Inc., Pittsburg, PA, 1992.
23. A. Altomare, M. C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi and G. Polidori, J. Appl. Crystallogr., 1994, 27, 435.
24. G. M. Sheldrick, SHELXL-93: Program for crystal structure refinement, University of Göttingen, Göttingen, Germany, 1993.
25. M. Nardelli, Comput. Chem., 1983, 7, 95; J. Appl. Crystallogr., 1995, 28, 659.
26. C. K. Johnson, ORTEP II, report ORNL-5138, Oak Ridge National Laboratory, Tennessee, USA, 1976.
27. Organic Solvents, ed. J. A. Riddick and W. B. Bunger, vol. II of Techniques of Organic Chemistry, Wiley-Interscience, NY, 3rd edn., 1970.
28. L. J. Bellamy, Advances in Infrared Group Frequencies, Chapman and Hall, London, 1975, (a)p. 143; (b)p. 141.
29. A. Gaset, L. Lafaille, A. Verdier and A. Lattes, Bull. Soc. Chim. Fr., 1968, 4108.
30. C. Hansch and A. Leo, Substituent constants for the correlation analysis in Chemistry and Biology, Wiley, NY, 1970.
31. M. Charton, in Design of Biopharmaceutical Properties through Prodrugs and Analogs, ed. E. B. Roche, American Pharmaceutical Association, Washington DC, 1977, p. 228.
32. The mixing of the sulfur lone pair with other group orbitals is not negligible, so that the sp³ hybridization assumed in the present discussion and in structures VI–IX is only an approximation. However, the HOMO of the studied compounds has prevailing sulfur character in agreement with the experimental UPS data ¹⁰ for compound 1.
33. G. Distefano, G. Granozzi, R. Bertoncello, P. R. Olivato and S. Guerrero, J. Chem. Soc., Perkin Trans. 2, 1987, 1459.
34. T. Kobayashi and S. Nagakura, Bull. Chem. Soc. Jpn., 1974, 47, 2563.
35. V. Y. Young and K. L. Cheng, J. Chem. Phys., 1976, 65, 3187.