Mass Spectral Study of Diastereomers on Electron Impact,III: 2-Bromo-3-Acetoxysuccinates and Tartrate Diacetates

The interaction between two carboalkoxy groups (COOR) and a bromine atom in stereoselective fragmentation is reflected in the mass spectra of dimethyl 2-bromo-3-acetoxysuccinates as has already been reported in the case of 2,3-dibromosuccinates. These results could be explained based on the expected most favourable conformations in the gas phase. In the case of dialkyl tartrate diacetates, the interaction between the two COOR groups is stereoselective, leading to different ions, and can be explained based on the preferred conformations as reported in the case of dialkyl tartrates. The mechanisms of formation of characteristic ions were confirmed using deuterium labelled compounds. Collision-induced dissociation spectra of [M – OR]⁺ ions from L-isomers of diacetates are different from those of the corresponding meso-isomers, showing a structural effect based on stereospecific interaction between the two COOR groups.