Quantifying Electrophilicity and Nucleophilicity

Herbert Mayr ,  Florian Seeliger ,  Stefan Berger 

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

Abstract

Reactions of donor stabilized carbocations with electron-rich π-systems and reactions of acceptor substituted carbanions with electron-poor π-systems are often treated as representatives of different classes of reactions - carbocation chemistry on one side, and carbanion chemistry on the other side.

We now demonstrate that the nucleophilicity parameters N and s, as defined by eq. 1 and previously derived from reactions of carbanions with benzhydrylium ions and quinone methides [1], can also be employed for describing the reactions of carbanions with various other types of Michael acceptors (Figure). In this way, carbocations and electron-deficient ethylenes can be located on a common electrophilicity scale while carbanions and electron-rich ethylenes can be located on a common nucleophilicity scale.

Figure. Plot of (log k)/s for the reactions of carbanions with electrophiles in DMSO at 20 °C versus the nucleophilicity parameters N of the carbanions. a) C6H4X = julolidyl


Figure shows that the slopes of (log k)/s plots versus the nucleophilicity parameters N of carbanions deviate from the slope of 1, indicating that eq. 1 does not properly describe these reactions, as previously reported for SN2 type reactions [2].

[1] H. Mayr, A. R. Ofial, Pure Appl. Chem. 2005, 77, 1807-1821.

[2] T. B. Phan, M. Breugst, H. Mayr, Angew. Chem. Int. Ed. 2006, 45, 3869-3874.

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  4. Towards a General Scale of Nucleophilicity?

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

Submitted: 2006-05-31 17:38
Revised:   2009-06-07 00:44
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