A meta effect in nonphotochemical processes: the homolytic chemistry of m-methoxyphenol

The m-methoxy group is normally electron-withdrawing (EW), sigma(m) = +0.12, sigma(m+) = +0.05. The strong EW activity of a phenoxyl radical's O* atom causes the m-methoxy group to become electron-donating (ED), sigma(m)(+) = -0.14. In valence bond terms, this can be ascribed to the nonclassical resonance structures 1c-e. Although it has long been known that m-methoxy is ED in photoexcited states, it has now been found to be ED for homolytic O-H bond breaking in ground-state 3-methoxyphenol.