Stereoelectronic effects at oxygen. The hydrolysis of 2-aryloxy-trans-1-oxadecalins

Abstract

The spontaneous hydrolysis of axial nitrophenyltetrahydropyranyl acetals with one or two trans ring junctions is 2–3 times slower than that of the equatorial isomers. It is concluded that relative reactivity depends not on stereoelectronic effects on transition states, but on differences in ground state energies. In the acid-catalysed reaction these relative reactivities are reversed, and k_ax > k_eq, apparently because of an additional barrier to the cleavage of the equatorial isomer. The evidence is consistent with this additional barrier being stereoelectronic in origin, but the effects are small, and other explanations cannot be ruled out.