N.M.R. spectra and stereochemistry of the bipyridyls. II. Dimethyl-substituted bridged biquaternary salts of 2,2'-bipyridyl

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Abstract
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.

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