Prof. Dr. Heinz A. Staab, Dipl.-Chem. Michael A. Zirnstein and Claus Krieger Benzo[1,2-h:4,3-h′]diquinoline (“1,14-Diazahelicene”): Synthesis, Structure, and Properties Angewandte Chemie International Edition in English 28
Despite almost equal N ⃛N distances in 1 and 2 (272.8 and 270.5 pm) the basicity constant of 2 is almost two powers of ten smaller than that of 1. The reason for this could be the helical structure of 2, which almost removes the destabilizing “lone-pair” interaction of the N atoms in the case of the free base and hinders an N ⃛H ⃛N bridge along the preferred directions of the “lone pairs” of the N atoms in the case of 2a.
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