13C N.M.R. STUDIES: PART III. CARBON-13 N.M.R. SPECTRA OF SUBSTITUTED ACETOPHENONES

Abstract
The 15.1 Mc/s 13C n.m.r. spectra of 55 substituted acetophenones have been examined and the chemical shifts of the various carbon nuclei determined. This series included a variety of monosubstituted cases (ortho, meta, and para) as well as several polysubstituted examples. The factors contributing to the observed shieldings of all carbon nuclei are considered. The aromatic shieldings are compared with previous results for other aromatic derivatives. The application of the carbonyl shifts to the study of steric inhibition of resonance in these derivatives is examined critically. The shieldings of the acetyl methyl and para-carbon nuclei are found to offer confirmatory evidence for the existence of steric hindrance to coplanarity of the acetyl group in several ortho-substituted cases.