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Results of kinetic studies of the condensed phase thermal reactions of the following biaryl hydrocarbons are reported; 1,l'-binaphthyl, 1,2'-binaphthyl, 1-phenylnaphthalene, and 9-phenylanthracene. Condensation generally occurred in parallel with both isomerization and dissociation and rates depended on concentrations of hydrogen donors. In order to simplify mechanisms, detailed studies used donors capable of providing just one H atom.These were xanthene, fluorene, and diphenylmethane. Condensation of 1,l'-binaphthyl in the presence of xanthene, the most effective donor, followed a second-order rate law (first order in both xanthene and binaphthyl concentration), k/M-' s-l = 106.9*0.6 exp(-36.0 f 2.0 kcal/RT) (360-560 "C). Fluorene was one-fifth as effective as xanthene while diphenylmethane was nearly inert. A mechanism is proposed in which the key intermediates in all reactions are radicals created by H-atom transfer to the biaryls. In the condensation of naphthyl-containing biaryls, it is suggested that reactions are initiated by H transfer to a position next to the condensation site. Details of the unimolecular steps leading to condensation and isomerization, however, remain unclear. Over the conditions studied, the reaction order with respect to donor varied between one and zero. It is proposed that this variability is a result of competition between two pathways for H transfer, one involving a simple, selective H transfer from the donor t o a biaryl molecule, the other involving a free H-atom intermediate.

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k , .a s-' 2.8 \ k:; M-' s-' k , , M-' s-' 4a-thiol addition k,, s-' k f , S-' 0.5 4.5 2.6 3.8 H, 0 solvent oxidations ( M -l s -l ) of I-3.0 95%EtOH 0 r " H o r ' s W W k , , s-'4a-peroxide dissociation a The k , values have been extrapolated to zero buffer concentration. Table V reveals that with a particular solvent, the values of AAG* (=AGlci -AGIN1) are similar for the reactions investigated (save the acid-catalyzed process associated with kl of pseudobase formation). This observation supports a greater electrophilicity of the 4a-position of the N' flavins when compared to the C1 flavins and a greater polarization of the peroxide moiety of the N1-4a-F1Et00H as compared to C1-4a-F1Et00H. Inspection of Table V also shows that the dissociation rate constants (for RS-, HO-, and HOO-) from the 4a-position of the N1 flavin are larger than those seen with the C' flavin. The ground states of C1-fix+Et and &+Et differ in free energy content by the same amount as the ground states of the products C1-4a-FlEtX and 4a-FlEtX. Lowering of the free-energy content of the transition state for addition of X must also lower the ground state for dissociation of X and by the same value of AAG*. Particularly noteworthy from Table V is the similarity of the AAG* for the N-and S-oxidation reactions in DMF to the AAG* for dissociation of peroxide from the C' and N' flavin hydroperoxides in that same solvent. Evidently the difference in polarization about the C,,-OOH bond in 4a-FlEt00H relative to CI-4a-FlEtOOH is reflected in the difference in polarization about the C b W H bond and in facilitation of the N-and S-oxidation reactions. Inspection ofFrom the present study, it is concluded that 1-carba-1-deaza FAD should, if recognized by the enzyme, serve as a cofactor for the hepatic flavoprotein microsomal oxidase in the N-oxidation of amines and the S-oxidation of sulfides.Acknowledgment. This work was supported by grants from the National Institutes of Health and the National Science Foundation. We should like to acknowledge the experimental con-

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