13C nuclear magnetic resonance studies. 61. The effect of solute–solvent association on internal rotation in substituted benzaldehydes

Abstract

Complete lineshape analyses of the 13C nmr signals of the ortho and meta carbons have been carried out for two p-substituted benzaldehydes in methylene chloride-d2 and toluene-d8 solutions over a wide temperature range. The activation parameters have been determined for the formyl group rotation and large negative values are found for ΔS≠ when the latter solvent is used. These results suggest that solute–solvent association has a steric effect on the transition state.