Why downfield proton chemical shifts are not reliable aromaticity indicators

Organic Letters

Volumn 7, Issue 16, 2005, Pages 3457-3460

  Faglioni, F ^a   Ligabue, A ^a   Pelloni, S ^a   Soncini, A ^a   Viglione, R G ^b   Ferraro, M B ^c   Zanasi, R ^b   Lazzeretti, P ^a  

^a UNIVERSITY OF MODENA AND REGGIO EMILIA   (Italy)

^b UNIVERSITY OF SALERNO   (Italy)

^c UNIVERSIDAD DE BUENOS AIRES   (Argentina)

Author keywords

[No Author keywords available]

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EID: 23944454338     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol051103v     Document Type: Article

References (34)

1. Wannere, C. S.; Corminboeuf, C.; Allen, W. D.; Schaefer, H. F., III; von Ragué Schleyer, P. Org. Lett. 2005, 7, 1457.
2. Pauling, L. J. Chem. Phys. 1936, 4, 673.
3. Lonsdale, K. Proc. R. Soc. (London) 1937, A159, 149.
4. London, F. J. Phys. Radium 1937, 8, 397, 7éme, Série.
5. Lazzeretti, P. Ring Currents. In Progress in Nuclear Magnetic Resonance Spectroscopy; Emsley, J. W., Feeney, J., Sutcliffe, L. H., Eds.; Elsevier: New York, 2000; Vol. 36, p. 1.
6. Gomes, J. A. N. F.; Mallion, R. B. Chem. Rev. 2001, 101, 1349.
7. von Ragué Schleyer, P. Chem. Rev. 2001 101, 1115 and refs cited therein.
8. Lazzeretti, P. Phys. Chem. Chem. Phys. 2004, 6, 217.
9. H)/2 and gives a measure of the effect of ring currents.
10. Viglione, R. G.; Zanasi, R.; Lazzeretti, P. Org. Lett. 2004, 6, 2265.
11. Soncini, A.; Fowler, P. W.; Lazzeretti, P.; Zanasi, R. Chem. Phys. Lett. 2005, 401, 164.
12. Ferraro, M. B.; Faglioni, F.; Ligabue, A.; Pelloni, S.; Lazzeretti, P. Magn. Res. Chem. 2005, 43, 316.
13. Flygare, W. H. Chem. Rev. 1974, 74, 653.
14. Ferraro, M. B.; Lazzeretti, P.; Viglione, R. G.; Zanasi, R. Chem. Phys. Lett. 2004, 390, 268.
15. Pelloni, S.; Ligabue, A.; Lazzeretti, P. Org. Lett. 2004, 6, 4451.
16. Cuesta, I. G.; Ligabue, A.; Sànchez de Meràs, A.; Lazzeretti, P. Chem. Phys. Lett. 2005, 401, 282.
17. 8
18. von Ragué Schleyer, P.; Maerker, C.; Dransfeld, A.; Jiao, H.; van Eikema Hommes, N. J. R. J. Am. Chem. Soc. 1996, 118, 6317.
19. Frisch, M. J. et al. Gaussian 98, revision A.7; Gaussian, Inc.: Pittsburgh, PA, 1998.
20. Zanasi, R. J. Chem. Phys. 1996, 105, 1460.
21. Lazzeretti, P.; Malagoli, M.; Zanasi, R. Technical report on project "sistemi informatici e calcolo parallele", Research Report 1/67, CNR, 1991.
22. Pople, J. A. Mol. Phys. 1958, 1, 175.
23. Havenith, R. W. A.; Engelberts, J. J.; Fowler, P. W.; Steiner, E.; van Lenthe, J. H.; Lazzeretti, P. Phys. Chem. Chem. Phys. 2004, 6, 289.
24. In the counterclockwise direction, from the C-C bond adjacent to the upper hexocyclic bond in Figure 1, 1.45, 1.36, 1.44, 1.42, 1.43, 1.36, 1.43, 1.42, 1.44, 1.36, 1.44, 1.38, 1.44 Å.
25. H(π), with the exception of H1. Our estimate is -4.99 ppm; that in ref 1 is -8.0 ppm. This value is anomalously high and hard to reconcile with the other estimates and with the current density maps.
26. Soncini, A.; Havenith, R. W. A.; Fowler, P. W.; Jenneskens, L. W.; Steiner, E. J. Org. Chem. 2002, 67, 4753. The RCM for 13 in this reference nicely agrees with that of Figure 1.
27. 15 via extended calculations for cyclobutane.
28. 15 and observing in the maps of Figure 1 that the maximum modulus of the current lies in the vicinity of the carbon nuclei in 13 and closer to the proton in 11.
29. H(π) values are incompatible with the RCMs of Figure 1.
30. H(π) in Table 1.
31. Havenith, R. W. A.; Lugli, F.; Fowler, P. W.; Steiner, E. J. Phys. Chem. A 2002, 106, 5703.
32. 1 is contradicted by our results in Table 1.
33. 1. The conviction of Wannere et al. is discounted by our investigations.
34. ∥(π) are, for 8, -2.4 and -2.1 ppm, respectively for the outer and inner rings. For 9, starting from the outer and moving to the inner ring, the calculated values are: -5.7, -8.2, and -11.5 ppm. Interestingly, the value corresponding to the midpoint of the C-C bond in the quasi-naphthalenic core is -12 ppm, very close to that of the inner rings. These pieces of information, fully consistent with the current plots and with other data discussed here, corroborate the conviction that, in the limit of long chains, hydrocarbons of type 9 have a quasi-naphthalenic kernel whose magnetic response is insensitive to removal of the methylene moieties at the ends.