Towards a General Scale of Nucleophilicity?

Thanh Binh Phan ,  Martin Breugst ,  Herbert Mayr 

LMU München, Department Chemie und Biochemie, Butenandtstrasse 5-13, München 81377, Germany

Abstract

Benzhydrylium ions and structurally related quinone methides have been employed as reference electrophiles for establishing a comprehensive nucleophilicity scale comprising π-, n- and σ-nucleophiles [1].

Bunting [2] and Richard [3] have previously shown that, with few exceptions, Ritchie´s N+ parameters (reactions with Ar3C+) are linearly correlated with Swain and Scott´s n parameters (reactions with CH3X).

We have now found that the rates of the SN2 reactions of a large variety of nucleophiles with the S-methyldibenzothiophenium ion correlate linearly with the N parameters derived from reactions with benzhydylium ions.

Scheme_1.jpg

We, therefore, propose a new correlation (equation 1) which describes reactions of nucleophiles with carbocations, Michael acceptors, and alkyl halides and includes previous nucleophilicity correlations as special cases [4].

Scheme_2.jpg

[1] a) R. Lucius, R. Loos, H. Mayr, Angew. Chem. 2002, 114, 97-102. b) Angew. Chem. Int. Ed. 2002, 41, 91-95.

[2] J. W. Bunting, J. M. Mason, C. K. M. Heo, J. Chem. Soc. Perkin Trans. 2 1994, 2291-2300.

[3] J. P. Richard, M. M. Toteva, J. Crugeiras, J. Am. Chem. Soc. 2000, 122, 1664-1674.

[4] T. B. Phan, M. Breugst, H. Mayr, Angew. Chem. Int. Ed. 2006, 45, 3868-3874.

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Presentation: oral at 18th Conference on Physical Organic Chemistry, Symposium 1, by Thanh Binh Phan
See On-line Journal of 18th Conference on Physical Organic Chemistry

Submitted: 2006-05-25 08:42
Revised:   2009-06-07 00:44
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