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The 2 and E isomers of N-methyl-a-(p-tolyl)-or-phenyl nitrone (7a and 8a) and the Z and E isomers of Nbenzyl-a-(p-tolyl)-a-phenyl nitrone (sa and 10) were prepared. Alkylations of isomeric oxime anions and the reaction of ,V-benzylhydroxylamine (13) with 1,l-dichloro-4'-methyldiphenylmethane (14) were employed in the syntheses. The first-order rates for thermal approach to geometric equilibrium of 7a, Sa, 9a, and 10 were determined in degassed tert-butyl alcohol solutions. Activation parameters for the isomerization of 9a were determined in the same solvent and are AE * = 33.6 i 1.4 kcal/mol; A S * = -4 & 4 eu. The energy barrier to isomerization is substantially larger than would be anticipated from the limited data available from previous studies of geometric isomerizations of nitrones. These results are briefly discussed.

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