The analysis of the n.m.r, spectra of 2,2?-, 3,3?-, and 4,4?-bipyridyl and three dimethyl-2,2?-bipyridyls is reported and the factors determining the relative chemical shifts of the ring protons and methyl groups in several solvents are discussed. The diamagnetic anisotropy of the neighbouring ring and electrostatic field effect of the nitrogen lone pair electrons are shown to be of roughly equal importance for derivatives of 2,2?-bipyridyl except in hydrogen bonding solvents. Attenuation of the electrostatic field effect in polar, and particularly in hydrogen bonding solvents, is established for 4- picoline, and for the bipyridyls, and this effect is responsible for striking changes in the spectrum of 2,2?-bipyridyl in hydrogen bonding solvents. An approximate interplanar angle of 58� is derived for 3,3?- dimethyl-2,2?-bipyridyl, and 2,2?-bipyridyl and its 4,4?- and 5,5?- dimethyl derivatives appear to be trans coplanar in all solvents. 3,3?- Bipyridyl and 4,4?-bipyridyl are probably highly twisted in all solvents, or alternatively, behave as essentially free rotors. The predicted conformations are in good agreement with the electronic spectral data.

ABMX analysis of the N.M.R. spectra of six bridged biquaternary salts of 2,2?-bipyridyl is reported. The difference in chemical shift between H3(3?) and H5(5?) varies with the length of the bridging group, and the results are discussed in relation to the probable conformation of the salts. The several factors determining the difference in chemical shift are discussed, and it is concluded that the diamagnetic anisotropy of the neighbouring pyridinium ring is the major contributor, with further significant contributions from the asymmetric distribution of positive charge in the pyridinium ring. Interplanar angles are calculated and compared with values estimated for the singly bridged biphenyls; evidence for mobile and frozen conformations is presented.

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The analysis of the N.M.R. spectra of nine dimethyl-substituted bridged biquaternary salts of 2,2?-bipyridyl is reported, and the results are discussed in relation to the several factors influencing the relative chemical shifts of heterocyclic ring protons and methyl group protons. Interplanar angles are calculated for all compounds and are shown to be in good agreement with angles estimated from molecular models and in qualitative agreement with electronic spectral data. Compounds with 3,3?-dimethyl substituents are shown to be in rigid dissymmetrically twisted conformations at room temperature, and evidence is presented that conformational inversion in the bipyridyl series is more difficult than in the corresponding singly bridged biphenyl series. Six of the compounds reported here have not previously been described.