MAGNETIC RESONANCE STUDY OF CONFORMATIONAL INVERSION IN SOME SUBSTITUTED 10,10-DIMETHYL-9,10-DIHYDROANTHRACENES

The ring inversion in 10,10-dimethyl-9-methylene-l,8-dichloro-9,10-dihydroanthracene (I), 9-(dichloromethylene)-10,10-dimethyl-9,10-dihydroanthracene (II), and 9-(dibromomethylene)-10,10-dimethyl-9,10-dihydroanthracene (III) in 1,1,2,2-tetrachloroethane solution has been studied using nmr complete line-shape analysis methods. Exchange rates were calculated from the nmr spectrum of methyl group protons by treating them as uncoupled exchanging AB systems with equal population. The low-field methyl peak in the spectra of compounds studied was assigned to the equatorial methyl and the high-field peak to the axial methyl. The ΔF‡ for ring inversion was found to be 15.9, 17.4, and 19.0 kcal/mol in compounds I, II, and III and qualitative interpretation was proposed in terms of nonbonded interactions between the exocyclic methylene substituents and the o-aryl substituents in the assumed planar transition state. The changes in the activation parameters obtained by using different 1/T2 values for line-shape calculations were also studied. © 1968, American Chemical Society. All rights reserved.