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The proton exchange of proton complexes of substituted benzenes has been studied by n.m.r. (40 and 60 Mclsec) in hydrogen fluoride between -105 and + 50°C. The added proton may exchange intramolecularly (eqn. (7) and (8)) in hexamethylbenzene and durene, or it may transfer to the aromatic molecule (eqn. (2)) or the solvent (eqn. ( 1)) in an intermolecular reaction. Considerable activation energies (8 kcal/mole) are involved in all transfers of the added proton from the CH2 or CH . CH3 group in the proton complex. This high energy may be related to the weakness of the interaction of the aliphatic CH2 group with the polar solvent. Proton exchange of H3O+ and HFT ions in HF is very rapid and nearly independent of temperature. 165* experimentalldetails have been published elsewhere.3.11 PROTON EXCHANGE OF WEAK BASESThe experimental assistance of Mr. J. Gaaf and Mr. F. J. Reinders is gratefully acknowledged. We thank Mr. H. Kippers for his help in the analogue computer calculations.

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Dipolar splittings with a quadratic dependence on static magnetic field strength are reported for selected pairs of nuclei in several porphyrins. These splittings are detectable as a result of a slight molecular alignment caused by the interaction of the static magnetic field with the anisotropic magnetic susceptibilities of the porphyrin rings. The magnitude of the splitting yields an effective value for Ax, the anisotropy of the susceptibility. This value includes association effects which may be estimated therefrom. Dipolar splittings between protons of attached vinyl groups can also be measured, and provide information about the average dihedral angle between the planes of the vinyl group and porphyrin ring.