The effect of charge and of electron density on the nuclear magnetic resonance parameters of conjugated systems: some isoelectronic anions and cations

Abstract

3-t-Butylaminoacrolein is readily O-protonated by trifluoroacetic acid and is N-deprotonated by sodium hydride in dimethyl sulphoxide, to give cationic and anionic species respectively, which both contain delocalised systems of 6π-electrons. The effect of the delocalisation is reflected in the equalisation of the vicinal coupling constants ³J_1,2 and ³J_2,3 compared with the neutral compound. The isoelectronic nature of the series is reflected in the similarity of ¹H and ¹³C n.m.r. chemical shifts for anion, cation, and neutral compound. The effect of the overall charge is shown by the regular increase of ¹J_CH through negatively, neutral, and positively charged systems. Similar results are obtained for glyoxal t-butylhydrazone.