Nine 4, 4′-substituted 2-isopropyl-2′-methoxybiphenyls were synthesized and temperature dependence of the NMR spectra of these compounds was examined. The effects of the substituents on the energy barrier to inversion of the biphenyl skeleton can be interpreted in terms of both resonance stabilization and out-of-plane bending of the axis bond at the transition state. In the latter, an electron-donating substituent makes the bond ...
