2,2 -Bipyridine conformational behavior

Fig. 6. Illustration of the difference in the conformational behavior of 2,2 -bipyridine and 1,10-phenanthroline on protonation.

The proton NMR spectrum of 2,2 -bipyridine has been obtained and analyzed in a variety of solvents by several authors. ° The full interpretation of the spectra is in accord with the transoid conformation I in solution. The behavior of the chemical shifts of protons at positions 3 and 3 indicates the existence of a strong deshielding effect exerted by the nitrogen atoms of the adjacent rings. Interestingly, the proton NMR spectra of 2,2 -bipyridine taken in various solvents indicate self-association and stacking of the molecules in some cases. The spectra of some substituted 2,2 -bipyridines, - - 2,3 -bipyridine, ° 2,4 -bipyridine, ° 3,3 -bipyri-dine, and 4,4 -bipyridine - - ° have been investigated in detail. It was... 

Allosteric behavior in a ditopic cavitand receptor has been induced via metal coordination [62]. Addition of Ag+ ions to a solution of a 2,2 -bipyridine-bridged biscavitand 56 switches the molecule from an S-shaped to a C-shaped conformation with the two cavities facing each other. At the same time two bis-cavitand molecules are brought together to give an overall tetratopic complex 57 (Figure 7.24). 

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