Mass spectra of some syn‐ and anti‐aromatic aldoximes

The mass spectra of eight pairs of geometric isomers of aromatic oximes and four other single aromatic oximes are reported. The loss of H 2 O, HO and HCN are major fragmentations from the molecular ion of all the benzaldoximes studies; however, the loss of HCN from the molecular ion did not occur in the oximes of 9‐phenanthraldehyde, 1‐naphthaldehyde and 2‐naphthaldehyde. The halogen substituted benzaldoximes eliminate HCNO and H 2 CNO forming an additional fragmentation pathway from the molecular ion. In general, variations were found for each pair of syn‐ and anti‐oximes but no consistent patterns could be found in the spectra for all the syn‐isomers versus all of the anti‐isomers. The geometric isomerism of four oximes previously reported in the literature have been established for the first time as anti‐m‐bromobenzaldoxime, syn‐9‐phenanthraldoxime, syn‐1‐naphthaldoxime and syn‐2‐naphthaldoxime. Three new oxime acetates were prepared and their mass spectra are discussed.