The electron impact induced fragmentation of aromatic aldoximes—III. On the loss of HCNO, OH⋅ and substituents and the role of substituent effects in the decomposition of cyclohexadiene type intermediate ions

Abstract The mechanisms for loss of HCNO, OH ˙ and the substituent X ˙ from aromatic aldosimes were elucidated with the aid of deuterium labelling, metastable ion characteristics and substituent effects. It is proposed that the loss of HCNO occurs through a cyclohexadiene type intermediate ion generated via a 6‐membered ring hydroxyl hydrogen transer to the ortho position of the phenyl ring. This is followd by a second step which involves the trnsfer of a hydrogen atom from the ortho position to C‐1. It is inferred from the corelation with the mesomeric effect (σ R + ) of substituents that this step is rate determining. Loss of OH ˙ and X ˙ proceed via the same cyclohexadiene type intermediate ion but, depending upon the substituent, other pathways are also followed.