EZ isomerization of 2,4-dinitrophenylhydrazones

Abstract

The acid-catalysed EZ isomerization of a series of α-substituted acetophenone 2,4-dinitrophenylhydrazones has been investigated. In contrast to reports by other workers on similar systems, the isomerization is influenced not only by steric effects but by polar effects as well indicating that it is probably incorrect to neglect in general the influence of polar effects on isomerizations about the –CN– bond. The correlation of the first-order rate constants with structural parameters and the mechanism of the isomerization (i.e. lateral shift vs. internal rotation) are discussed.