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

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.

Diquats with Robust Chirality: Facile Resolution, Synthesis of Chiral Dyes, and Application as Selectors in Chiral Analysis

“…It is possible to distinguish in early reportse xamples of diquat derivatives with potentially elevated configurational stability.S potswood andT anzer studied as eries of dimethyl-substitutedd iquats with aliphatic bridge [6] and Vçgtle and Bombach reported diquats made by simple quaternization of several 2,2'-bipyridinesw ith o-xylylene dibromide. [7] However,t he configurational stability and resolution of the enantiomers were not addressed in theser eports.M ore recently,t he Lacour groupr evisiteds omeo ft hese dications (Scheme 1b), and reportedt he resolution and determination of racemization barriers.…”