Mechanisms of acid catalyzed Z/E isomerization of hydroximates

The acid-catalyzed isomerization of methyl O-methylcinnamohydroximate (1Zb and 1Eb) was investigated with four different acids in acetonitrile at 25 °C. There are two reasonable mechanisms in which isomerization can take place. The first being nucleophilic catalysis, where the acid counter ion undergoes nucleophilic attack on the protonated carbon-nitrogen bond. Rotation about the carbon-nitrogen single bond of the tetrahedral intermediate leads to Z/E isomerization. The second method is iminium ion rotation where the nitrogen atom of the carbon-nitrogen double bond is protonated, followed by rotation around the weakened carbon-nitrogen double bond. It is believed that the rates of isomerization will be higher than rates studied previously. However, our results were inconclusive.