Conformational Preferences of ortho-Substituted Benzophenones. Correlations Between Carbon-13 Nuclear Magnetic Resonance Shieldings and Calculated Torsional Angles

Abstract

The results of an investigation of the conformational properties of some benzophenones are reported. Carbon-13 n.m.r. spectra provide a generally applicable method to study the conformational preference of these compounds through the C=O shifts. Semi-empirical conformational energy calculations have been used to build contour maps of relative conformational energy as a function of the two internal rotation angles of these molecules. Conformations of minimum energy, as detected from the contour maps, have been assumed as the most stable. The phenyl torsional angles corresponding to these conformations, plotted against the C=O shifts, furnish linear relationships.