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.
Foti
Mario C
MC
Istituto di Chimica Biomolecolare del CNR, Via del Santuario 110, I-95028 Valverde (CT) Italy. mario.foti@icb.cnr.it
Daquino
Carmelo
C
DiLabio
Gino A
GA
Ingold
K U
KU
D000840:Anisoles / Q000737:chemistry*; D010777:Photochemistry; D013816:Thermodynamics
D000840:Anisoles; C094702:3-hydroxyanisole