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B. PERL,iND FARRINGTON DANIELS
data on the rates of racemization of biphenyl compounds, shows that the potential barrier niust be less than 20 kcal. This low value seems to us to rule out definitely the coplanar configuration of dianthrone as an explanation of state 2 . The betaine structure of dianthrone, having no uncoupled spins, is presumably one of several valence bond structures which must be considered in deriving the real resonance state of the molecule. A priori, i t is possible that states 1 and 2 are two related resonance states, for instance one even and the other odd. This would account for the observed selection rules, but Professor I
