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 Plenary Lecture Abstract 

Stephen F. Nelsen

   65th Birthday Symposium
Madison, Wisconsin
June 3-4, 2005

Roger W. Alder

School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK BS8 1TS. E-mail: rog.alder@bristol.ac.uk; Fax: 144 117 9298611; Tel: 144 117 928765

From Proton Sponges to C₂-chiral diamines with pK_as near 25

The original Proton Sponge^® 1a is 6 pK_a units stronger than typical aromatic amines. ¹ The strongest proton sponges known to date, 1b, ² 2, ³ and 3 ⁴ have pK_a values in water of 16-17 (11-12 in DMSO; 25-6 in MeCN), but there is still considerable debate about the reasons for the enhanced basicities of these compounds. ⁵ It will be argued that strain relief on protonation is the overwhelmingly dominant factor and, on the basis of this analysis and DFT calculations, new diamines (e.g. 4-6) have been designed which are predicted to have pK_a values in water of around 25 (32 in MeCN). Moreover it can be predicted that 4-6 will show useful rates of proton transfer unlike 7 where the inside proton can be neither inserted nor removed by conventional proton transfers. ⁶ An analysis of the stereoisomers (including in-/out-isomers ⁷ ) of 15,16-dimethyl-15,16-diazatricyclo[9.3.1.1^4,8]hexadecane (4 is the 1R,4R,8R,11R-isomer) predicts that pK_a values will vary by >14 log units.

References

¹              R. W. Alder, P. S. Bowman, W. R. S. Steele, and D. R. Winterman, Chem. Commun., 1968, 723.

²              R. W. Alder, N. C. Goode, N. Miller, F. Hibbert, K. P. P. Hunte, and H. J. Robbins, J. Chem. Soc., Chem. Commun., 1978, 89.

³              B. Kovacevic and Z. B. Maksic, Chem.‑Eur. J., 2002, 8, 1694; V. Raab, M. Harms, J. Sundermeyer, B. Kovacevic, and Z. B. Maksic, J. Org. Chem., 2003, 68, 8790.

⁴              R. W. Alder, P. Eastment, N. M. Hext, R. E. Moss, A. G. Orpen, and J. M. White, J. Chem. Soc., Chem. Commun., 1988, 1528.

⁵              R. W. Alder, Chem. Rev., 1989, 89, 1215; A. F. Pozharskii, O. V. Ryabtsova, V. A. Ozeryanskii, A. V. Degtyarev, O. N. Kazheva, G. G. Alexandrov, and O. A. Dyachenko, J. Org. Chem., 2003, 68, 10109.

⁶              R. W. Alder, A. Casson, and R. B. Sessions, J. Am. Chem. Soc., 1979, 101, 3652; R. W. Alder, Tetrahedron, 1990, 46, 683.

⁷              R. W. Alder and S. P. East, Chem. Rev. (Washington, D. C.), 1996, 96, 2097.

Biographical sketch

Roger Alder has been at the University of Bristol since 1965 and is now an Emeritus Professor of Organic Chemistry. His major research interest has been in the physical organic study of novel molecules, including proton sponges, medium‑ring bicyclic structures and in/out isomerism, novel types of polymers with strong conformational control and, most recently, stable carbenes.

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