Dynamic Structure of the Potent Uncoupler SF 6847 (3,5-Di-t-butyl-4-hydroxybenzylidenemalononitrile) and Its Derivatives

Abstract

Abstract The steric and electronic structures of the most potent uncoupler of oxidative phosphorylation known, SF 6847, and its derivatives were studied. 1H and 13C NMR measurements showed that the malononitrile moiety is not planar with the benzene ring and that its intramolecular motional freedom is reduced on acid dissociation of the phenolic proton. The activation energies of the tumbling motion of the malononitrile moiety in the anionic forms of SF 6847 and its derivatives were also determined from their 1H NMR measured at various temperatures. The CNDO/2 and ab initio MO calculations of the model compounds of SF 6847 showed that the planar form is quite unstable and that the malononitrile moiety is twisted considerably relative to the benzene ring. The effect of the dynamic structure on the acidity of SF 6847 was discussed based on the above results.