Nuclear magnetic resonance studies on benzaldehydes. Part II. Carbon-13 nuclear magnetic resonance studies of the barrier to internal rotation and the conformational equilibrium in o- and m-substituted benzaldehydes

Abstract

The O-cis : O-trans population ratio of several unsymmetrically substituted benzaldehydes has been measured by means of ¹³C Fourier transform n.m.r. spectroscopy at –150°, where the O-cis–O-trans exchange is frozen out. The barrier to internal rotation about the phenyl–formly bond was estimated by application of dynamic n.m.r. methods to the ¹³C spectra at ca.–120°. ΔG^‡ Values are ca. 30 kJ mol^–1.