Ortho Effects in Organic Molecules on Electron Impact. VIII. Intramolecular Aromatic Substitution in (Arylmethylene)barbituric Acids

Mass spectral decomposition process involving intramolecular aromatic substitution with the ejection of either the hydrogen or the substituent in the ortho position from the M+· ion is noticed in the eleven 5-(arylmethylene) barbituric acids studied. It has been generally noticed that for such a cyclization to occur, the presence of an α,β-unsaturated carbonyl function, in conjugation with the ring, is essential in aromatic systems.