2,2’-bipyridine conformation

The structure of a non-hydrolyzed dimer, cA-[(2,2 -bipyridine)palladium(II)]2(/i-l,3-N03)2 2+ is shown in Figure 45.521 The dimerized m-( 2.2-bi pyridine) Pd11 units aggregate into a dimer-to-dimer linear conformation through direct metal—metal interaction522 and tt-tt stacking.523 Notably, the dimer was first reported to be linked by double nitrato-bridges (/x-l,3-N03)2 in a cofacial... 

Fig. 10 Wave-like ribbon structure of (C-methylcalix[4]resorcinarene).2(4,4 -bipyridine) (CH3CN) with C-methylcalix[4]resorcinarene in a bowl conformation [52]...

There has been much interest in the predominant conformation of the bipyridines. Theoretical studies of the molecular structure of 2,2 -bipyridine suggest that the conformation with the nitrogen atoms transoid to one another is more stable than the cisoid In 3,3 -bipyridine,... 

The dipole moment of 2,2 -bipyridine in benzene or carbon tetrachloride has been reported as less than 0.68, 0.91, 0.69, and 0.61 d. Because the conformation with the two nitrogen atoms transoid to each other should have a zero dipole moment and the cisoid configuration a value of 3.8 D, the consensus is that the molecule is in the transoid conformation and is approximately planar in solution with an angle of about 20° between... 

The IR spectra of 2,3 -bipyridine,i " - ° - i 2,4 -bipyridine, " 3,3 -bipyridine, °° and 3,4 -bipyridine °°- have all been reported. From IR spectral assignments it is suggested that 2,3 - and 3,3 -bipyridines adopt the cisoid conformation. The IR spectrum of 4,4 -bipyridine both in the solid state and in solution has attracted much attention, and the spectrum has been fully interpreted.4,4 -Bipyridine has been included in a study of the use of IR intensities as a quantitative measure of intramolecular interactions. Interestingly, changes in the intensities of IR bands due to aromatic ring deformations and C—H deformations on going from the solid to the molten state have been used to show that the aromatic rings of 2,2 - and 4,4 -bipyridines are not coplanar in the liquid phase. The IR spectra of salts of 4,4 -bipyridine have been discussed. ... 

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... 

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

Calculations indicate that the planar s-trans conformation is 20-28 kJ mol 1 more stable than the s-cis form owing mainly to the interaction of the lone pairs.112 Furthermore, it appears that the rc-acceptor properties of the N=C—C=N skeleton increase in the sequence 2,2 -bipyridine < 2-pyridinecarbaldehyde-iV-methylimine < R-DAB.116... 

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