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Prof. Dr. Heinz A. Staab and Dr. Thomas Saupe “Proton Sponges” and the Geometry of Hydrogen Bonds: Aromatic Nitrogen Bases with Exceptional Basicities Angewandte Chemie International Edition in English 27

Version of Record online: 30 DEC 2003 | DOI: 10.1002/anie.198808653

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The fully unexpected high basicity of “proton sponges” such as 1 and 2 is due to spatial interaction of the basic centers, which are in close proximity. The two factors which are most important in causing this effect are, on the one hand, the extreme steric strain in these systems and the destabilizing effect of the overlap of the nitrogen lone electron pairs in 1 and 2 and, on the other, the strong NċHċN hydrogen bonds which are formed on monoprotonation to 1a and 2a, respectively, and which lead to considerable relaxation of the steric strain. 1, the classical proton sponge, is protonated and deprotonated extraordinarily slowly. 2, a novel species without any hydrophobic shielding, is, by way of contrast, a very strong and kinetically active base.

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