Stereospecific alcohol elimination from dialkyl mesaconates under electron impact: Another example of a hidden hydrogen transfer

Under electron impact dimethyl and diethyl mesaconates give rise to abundant M ? MeOH]⁺ and M ? EtOH]⁺ ions, respectively. The geometrically isomeric citraconates yield M ? MeO]⁺ and M ? EtO]⁺ ions. Mixed methyl ethyl mesaconates eliminate both methanol and ethanol. These findings, together with the results of a deuterium labelling study, indicate that the elimination of alcohol from the molecular ions of the mesaconates is partially preceded by a hidden hydrogen transfer step.