Electric field effects in magnetic resonance. Part I. 13C chemical shifts

Abstract

The ¹³C magnetic resonance spectra of 19 complexes of acetylacetone have been recorded and are compared with their ¹H spectra and the i.r. stretching frequencies of the ring atoms. The ¹³C shifts of the CH₃ and ring CH groups for first- and second-row elements are explained largely in terms of first-order electric field shifts, the coefficients of proportionality between the ¹³C and ¹H shifts being ca.–4·2 for CH₃ and +0·9₄ for CH. The CO ¹³C shifts appear to be related to the CO and CC i.r. stretching frequencies. Serious deviations from these generalisations are observed for elements with filled or partly filled d-orbitals.