Mass spectrometric studies. V. Benzylidenemalonic acid and related compounds

The mass spectra of benzylidenemalonic acids are dominated by dehydration to species formulated as anhydrides, except in cases where ortho effects alter the fragmentation. Furfurylidenemalonic acid shows a novel rearrangement process involving an oxygen atom transfer. The mass spectra of the corresponding dimethyl and monomethyl esters have also been examined. The former show marked methoxy group migrations, whereas the latter have spectra in which fragmentation processes characteristic of both the parent acids and the diesters are observed.