THE PROTON RESONANCE SPECTRA AND STRUCTURES OF SUBSTITUTED AZULENES IN TRIFLUOROACETIC ACID

Abstract

The proton resonance spectra for a number of substituted azulenes and their conjugate acids are reported at 22 °C. From the spectra for the conjugate acids it is confirmed that monoprotonation occurs in the five-membered ring in each case. The unit electron deficiency is shown to be mainly localized in the seven-membered ring of the ion.Chemical shift changes on protonation are interpreted qualitatively in terms of changes in local π electron charge densities on the carbon atoms.Unusually large values are noted for the coupling constants between protons on the five-membered ring of the cations and are attributed in part to hyperconjugative effects.