MASS-SPECTRAL STUDY OF DIASTEREOMERS BY ELECTRON-IMPACT

The electron impact mass spectra of some diastereomeric dialkyl tartra tes and isopropylidine derivatives of dimethyl tartrate show diagnosti c differences in the relative abundances of some ions. The differences have been explained based on preferred conformations of these isomers . The configuration of the carbomethoxy groups has been correlated wit h the configuration of carbomethoxy groups in dimethyl maleate and fum arate. The interaction between the two carbomethoxy groups is relative ly larger in conformations where there is a gauche interaction between them. The results could also be correlated with the solution phase co nformations of these compounds reported in the literature using nuclea r magnetic resonance techniques. The difference, which is small in dia stereomeric dimethyl tartrates, is very reproducible and has been conf irmed using six different mass spectrometers.