Electron impact studies. Part CIV. Cyclisation reactions of negative ions. The o-O2NC6H4(CHCH)nCOR system

Abstract

Negative-ion mass spectra of compounds of the general type o-O₂NC₆H₄(CHCH)_nCOR (n= 1–3) show rearrangement peaks produced by novel cyclisation reactions occurring between the adjacent substituents. When n= 1. reactions proceed mainly through six- and seven-membered transition states, whereas for n= 2, six-centred states still predominate, but reactions also occur via five-membered transition states. Major fragment ions correspond to charged 1,2-dicarbonyl (n= 1), 2-ene-1,4-dicarbonyl (n= 2), and 2,4-diene-1,6-dicarbonyl (n= 3) systems. Rearrangement ions are not observed when the nitro-group is replaced by a carboxy-group.